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Third generation dual source CT with ultra-high pitch protocol for TAVI planning and coronary tree assessment: feasibility, image quality and diagnostic performance
European Journal of Radiology 122 (2020) 108749
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European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
Research article
Third generation dual source CT with ultra-high pitch protocol for TAVI planning and coronary tree assessment: feasibility, image quality and diagnostic performance
T
Nicolò Schicchia, Marco Fogantea,*, Paolo Esposto Pirania, Giacomo Agliataa, Tommaso Pivab, Corrado Tagliatia, Matteo Marcuccia, Antonio Franciosoa, Andrea Giovagnonia a b
Radiology Department, Azienda Ospedaliero Universitaria “Ospedali Riuniti”, 60126, Ancona, Italy Cardiologic Department, Azienda Ospedaliero Universitaria “Ospedali Riuniti”, 60126, Ancona, Italy
A R T I C LE I N FO
A B S T R A C T
Keywords: DSCT TAVI Coronary calcium scoring Coronary assessment Aortic valve
Purpose: To evaluate the feasibility, image quality (IQ) and diagnostic performance of third generation 192 × 2 dual source computer tomography (DSCT) with ultra-high pitch acquisition for trans-catheter aortic valve implantation (TAVI) planning and coronary tree assessment. Method: In this prospective study, 223 patients underwent to DSCT for TAVI. Coronary calcium scoring (CCS) was calculated. Attenuation values were measured at aortic levels, femoral and coronary arteries. IQ was evaluate with a 4-point scale. The CT performance, in the assessment of coronary stenosis ≥50 % and ≥70 %, was compared with invasive coronary angiography (ICA), served as reference standard. Aortic annulus (AoA) CT derived area and implanted prosthesis size were correlate with Spearman’s test. Results: Attenuation values > 400HU were obtain in all segments. IQ median value was ≥ 3. In the assessment of stenosis ≥50 %, on a segment-based analysis, CT sensitivity, specificity, positive and negative predictive values and diagnostic accuracy were 97.6 %, 87.6 %, 64.2 %, 99.0 % and 89.6 %, on patient-based analysis were 97.8 %, 88.8 %, 68.8 %, 99.4 % and 90.6 %, respectively. In the assessment of stenosis ≥70 %, on segmentbased analysis, were 88.5 %, 83.8 %, 54.7 %, 96.8 % and 84.8 %, and on patient-based analysis were 92.5 %, 85.8 %, 58.7 %, 98.1 % and 87.0 %, respectively. The CT performed better in the group with lower CCS. A direct correlation was found between AoA CT derived area and prosthesis size. Conclusion: DSCT, using a single prospective ECG-triggered ultra-high pitch acquisition, is feasible for TAVI planning and in the assessment of coronary stenosis. CT performed worse in patients with severe coronary calcifications.
1. Introduction Aortic stenosis is the most prevalent valve heart disease in developed western countries [1]. Trans-catheter aortic valve implantation (TAVI) is a safe treatment for patients with severe symptomatic aortic stenosis [2,3]. Invasive coronary angiography (ICA) is recommended for pre-procedural TAVI due to possible harmful of coronary artery stenosis on procedural outcome and prognosis if left untreated. However, only one third of all ICAs are performed with a revascularization procedure, while the rest only for diagnostic purpose [4,5]. Moreover, ICA is not ideal as a widespread diagnostic procedure, due partly to its high cost, but mostly because of the associated mortality and morbidity [6].
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Computed tomography (CT) is part of the routine TAVI planning for sizing the valve prosthesis and assessment of the access route [7]. Moreover, CT is used to rule out significant coronary stenosis with low to intermediate pre-test probability for coronary artery disease (CAD) [8]. A holistic CT evaluation of aorta, peripheral vessels and coronary arteries pre-TAVI procedure could lead to a reduction of unnecessary ICA and, consequently, of cumulative radiation dose, contrast volume and risk management. The introduction of third generation dual source (DS) CT scanners provided a new ultra-high pitch protocol with very low acquisition time, that allows reducing any motion artefacts [9,10]. In recent studies, the use of third generation DSCT with ultra-high pitch protocol for TAVI planning have demonstrated excellent results, but no one
Corresponding author. E-mail address: [email protected] (M. Fogante).
https://doi.org/10.1016/j.ejrad.2019.108749 Received 3 August 2019; Received in revised form 7 November 2019; Accepted 12 November 2019 0720-048X/ © 2019 Elsevier B.V. All rights reserved.
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performed: a small (200 mm) and large (300 mm) field of view data set for the assessment of the aortic root and coronary tree (cardiac reconstruction) and the ilio-femoral accesses (vascular reconstruction), respectively.
included coronary tree assessment [11–14]. Furthermore, due to age and comorbidities, heavy coronary calcifications and high coronary calcium scoring (CCS) challenge the diagnostic performance of CT [15,16]. The aim of this study is to evaluate the feasibility, the image quality and the diagnostic performance of third generation DSCT with ultrahigh pitch protocol for TAVI planning and coronary tree assessment and the impact of CCS on the diagnostic performance.
2.3. Aortic annulus measurements and contrast attenuation evaluation For aortic annulus (AoA) measurements, the CT data sets were analysed using a computer-aided evaluation software (syngo.via, version VB10A; Siemens Healthcare, Erlangen, Germany) with clinical application “CT TAVI Planning”. Detailed measures of the aortic root anatomy focused on AoA dimensions, such as minimum and maximum diameters, area and the distance from the AoA to the coronary ostia were evaluated by two expert radiologist (both with ≥10 years of clinical experience in coronary CT angiography performance and analysis), as recommended by the SCCT expert consensus document [17]. For any disagreement in CT data analysis between the two readers, consensus was achieved. For each patient, contrast attenuation value, expressed as HU, and the corresponding standard deviation (SD), as indicator for image noise, were measured by one expert radiologist (with ≥10 years of clinical experience in coronary CT angiography performance and analysis) with ROIs placed on axial images at three different levels of the aorta (aortic root, descending thoracic aorta, sub-renal abdominal aorta) and middle third of the right and left common femoral arteries. Additional circular ROIs were placed into the right lobe of the liver with no vascular structures to calculate the contrast-to-noise ratio (CNR), as follow:
2. Material and methods 2.1. Study population The Institutional Review Board of our Hospital approved the study protocol. Written informed consent was obtained from all patients. In this prospective study, between April 2018 and April 2019, were included 236 consecutive patients, referred to our Hospital for CT and ICA for TAVI planning. In all patients, ICA was performed at least 3 days after CT. Exclusion criteria were: severe adverse reactions to an iodinated contrast agent (n = 5), and estimated glomerular filtration rate < 30 ml/min/1.73m2 (n = 8). Final study cohort was composed by 223 patients. 2.2. CT protocol All CT examinations were performed using a 384(192 × 2)-slices third generation DSCT scanner (SOMATOM Force CT; Siemens Healthineers, Forchheim, Germany) with patients in supine position and feet towards the gantry. A 20-gauce cannula was inserted into superficial vein of the right antecubital fossa, connected to a two-way injector (EmpowerCTA®+ Injector System; Bracco Injeneering, Lausanne, Switzerland). No premedication with beta-blockers or nitrates was added before CT acquisition. All patients were examined with the same standardized examination protocol. First, a non-contrastenhanced prospective electrocardiogram (ECG) -triggered scan was acquired with a tube voltage of 120 kV and scan range from carina to diaphragmatic level, in patients without stents or coronary artery bypass graft. Then, a contrast-enhanced scan was acquired. All patients received 60 ml of contrast medium (Iomeprol, 400 mgI/ml; Bracco Imaging, Milan, Italy) at flow rate of 5 ml/s followed by 50 ml of saline solution at 4.8 ml/s. Scan parameters are summarized in Table 1. Scan protocol consisted in a single prospective ECG-gated ultra-high pitch (pitch factor, 3.2) acquisition. Acquisition started when region of interest (ROI) value at the aortic diaphragmatic level reached 240 Hounsfield Unit (HU). Coronary arteries images were acquired at 30 % of R-peak-to-R-peak. For each patient, two reconstructions were
CNR = (vessel attenuation – liver attenuation) / image noise
2.4. Coronary calcium scoring and coronary arteries assessment The CCS was calculated, by one expert radiologist (with ≥ 10 years of clinical experience in coronary CT angiography performance and analysis) as previously described [18], using a dedicated computeraided evaluation software (syngo.via, version VB10A; Siemens Healthcare, Erlangen, Germany) with clinical application “Cardiac Calcium Scoring”; instead, for coronary arteries assessment was used the clinical application “CT Cardiac”. The image quality and the presence and the degree of coronary stenosis were evaluated by two radiologists (both with ≥ 10 years of clinical experience in coronary CT angiography performance and analysis). Coronary arteries were segmented as suggested by the American Heart Association [19]. To evaluate semi-qualitative image quality score for each native coronary artery, stent, and CABG was used a 4-point Likert image
Table 1 Contrast-enhanced CT scan parameters. Acquisition parameters Scan technique Scan direction (from – to) Scan interval (from – to) Gantry rotation time (s) Pitch factor Tube voltage Tube current
Bolus tracking Cranio – caudal Lung apexes – ischium 0.22 3.2 Automatic modulation (CARE kV, Siemens Healthineers) Automatic modulation (CARE kV, Siemens Healthineers)
Slice thickness – Slice increment (mm) Kernel Iterative reconstruction algorithm Slice thickness – Slice increment (mm) Kernel Iterative reconstruction algorithm
0.6 – 0.4 Bobyvascular 40 ADMIRE (Siemens Healthcare) – strength 4 1 – 0.7 Bodyvascular 44 ADMIRE (Siemens Healthcare) – strength 3
Reconstruction parameters Cardiac reconstruction
Vascular reconstruction
Abbreviations. – ADMIRE: advanced modeled iterative reconstruction. 2
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calculated. The CT diagnostic performance per-segment and per-patient analysis in the assessment of coronary stenosis ≥50 % and ≥70 % was determined against the reference standard ICA.Chi-square test was used to compare semi-qualitative image quality of coronary arteries in two subgroups with CCS < 400 and ≥400. The CT diagnostic performance per-segment and per-patient analysis in the assessment of coronary stenosis ≥50 % and ≥70 % was determined against the reference standard ICA in subgroups with CCS < 400 and ≥400 and in subgroups with CCS < 600 and ≥600. The Cohen’s Kappa test (k) was used to evaluate the inter-observer agreement. The Spearman’s correlation test (r) was used to correlate AoA CT derived area with implanted prosthesis size. Mean DLP and ED values were calculated. A p value < 0.05 was considered statistically significant.
quality score: 1 poor/not diagnostic: impaired image quality limited by excessive noise or poor vessel wall definition; 2 adequate: reduced image quality either poor vessel wall definition or excessive image noise; 3 good: effect of image noise, limitations of low contrast resolution, and vessel margin definition are minimal; 4 excellent: excellent attenuation of the vessel lumen and clear delineation of vessel walls. For each patient, contrast attenuation value, expressed as HU, and the corresponding SD, as indicator for image noise, were measured by ROIs placed in the proximal tract of each coronary arteries. Additional circular ROIs were placed into the surrounding tissue of the aortic root immediately cranial to the left main coronary artery to calculate the noise ratio CNR, as follow:
3. Results 3.1. Study population characteristics
CNR = (coronary attenuation – surrounding tissue) / image noise.
The mean age was 79.2 ± 4.9 years. Mean heart rate during examinations was 66.2 ± 9.8 beats per minute. 44/223 (19.7 %) patients had arrhythmic or high heart rate, ≥65 beats per minute (bpm). Mean CT scan time was 1.95 ± 0.12 s [0.96–2.5 s]. The mean CCS was 733.1 ± 375.6 (299.4–1810.8). Patients with stent were 78 and with CABGs were 37. Total stents were 115 and total CABGs were 51.
Curved planar reformation images were used to rule out in all the native coronary arteries the presence of stenosis ≥50 % and ≥70 %. Moreover, all the stented segments were evaluated for the presence of significant intra stent restenosis (ISR) (defined as a lumen diameter reduction more than 50 %) and by-pass grafts stenosis with softwareaid evaluation. Results were also reported in subgroups of patients defined by CCS < 400 and ≥400 and in subgroups of patients defined by CCS < 600 and ≥600.
3.2. Aortic annulus measurements and contrast attenuation values Mean minimum diameter of the AoA was 19.4 ± 1.8 mm (range, 17–26 mm); mean maximum diameter was 27.9 ± 2.9 mm (range, 22–32 mm) and mean area was 451.4 ± 76.4 mm2 (range, 306–656 mm2). Mean distance of the AoA plane to the left coronary ostium was 14.1 ± 2.8 mm (range, 9–19 mm) and to the right coronary ostium was 16.7 ± 4.7 mm (range, 11–31 mm). The overall mean attenuation values and CNRs of aortic segments and common iliac arteries were > 500 HU and < 20, respectively (Table 2). CT imaging examples of AoA and vessels evaluation are shown in Figs. 1 and 2.
2.5. Invasive coronary angiography All patients included in our study underwent ICA within 1 month before the TAVI procedure. ICA procedures were performed with standard technique by two operators with more than 15 years of clinical experience blinded to CT results. Angiograms were examined using a quantitative coronary angiography software (QantCor, QCA; Pie Medical Imaging, Maastricht, Netherlands).
3.3. Coronary arteries assessment
2.6. TAVI procedure outcome
Mean contrast attenuation values and CNR values of the coronary arteries are summarized in Table 3. 3179 coronary segments on 3345 (95.0 %) were considered as evaluable. In 166/3345 (5.0 %) segments the image quality score was poor/not-diagnostic because of large calcifications (125 segments) and motion artefacts due to incomplete breath holding/movements (41 segments). CT demonstrated an overall evaluability of ISR and CABGs stenosis of 85.2 % and 100.0 %, respectively. Semi-qualitative image quality median values for coronary arteries were ≥3. The patients with stenosis ≥50 % and ≥70 % were 45 and 40, respectively. Table 4 shows CT sensitivity, specificity, PPV, NPV and diagnostic accuracy for assessment of stenosis ≥50 % and ≥70 % in comparison with ICA, considering poor/non-diagnostic images as positive for stenosis ≥50 % and ≥70 %. Fig. 3 shows an example of comparison between ICA and CT in coronary arteries assessment. Semi-qualitative image quality median values for stents and
TAVI procedure success was defined accordingly to correct device, annular rupture, evidence of prosthesis instability, and peri-procedural mortality. AoA CT derived area was compared with implanted prosthesis size. 2.7. Radiation dose The dose-length product (DLP) and the effective dose (ED) of each CT were evaluated. The ED was calculated as the DLP multiplied for a conversion coefficient for the chest k = 0.014 mSv/mGy*cm and for abdomen k = 0.015 mSv/mGy*cm. Because of the scan protocol including both thorax and abdomen, an average conversion factor k = 0.015 mSv/mGy*cm was used [20]. 2.8. Statistical analysis
Table 2 Overall mean quantitative parameters for aorta and peripheral accesses.
Statistical analysis was performed with the SPSS v.17.0 software (SPSS Inc; Chicago, IL). Continuous variables were expressed as mean ± SD, and discrete variables were expressed as absolute numbers and percentages. Mean minimum diameter, maximum diameter, area of the AoA, and the distance of the AoA to the coronary ostia were calculated. Mean attenuation and CNR in each vascular segment were calculated. Semiqualitative image quality of coronary arteries, stents and CABGs were 3
Vessel segment
Mean HU
Aortic root Descending aorta Subrenal aorta Right common femoral artery Left common femoral artery
521.1 537.8 545.2 553.5 548.1
± ± ± ± ±
Mean CNR 50.4 59.2 55.7 65.2 67.8
15.1 14.1 16.1 18.5 19.1
± ± ± ± ±
3.6 4.1 3.2 6.7 5.9
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Fig. 1. Aortic annulus evaluation in a 73-year-old female patient undergoing 192 × 2-DSCT for TAVI planning. The centre axis of left ventricle outflow tract and aortic root were chosen as reference with the 3 orthogonal planes. The longitudinal axis in coronal and sagittal views were aligned (A, B). The transverse plane was aligned at the lowest level of the valve until the hinge points of the aortic leaflets were depictable (C). Aortic annulus was defined as a virtual ring formed by joining the basal attachments of the aortic leaflets. Maximum diameter, minimum diameter, and area were measured at this level.
CABGs were ≥3. The patients with ISR were 27 and the patients with CABGs stenosis were 20. Table 5 shows, on a patient-based and vesselbased analysis, CT diagnostic performance in the assessment of ISR and CABGs stenosis, considering poor/non-diagnostic images as positive for ISR and CABGs stenosis.
found between CT derived area and implanted prosthesis size (r = 0.98, p < 0.001). In 7/223 patients (3.1 %) CT measurements were oversized, while in 9/223 patients (4.0 %) an undersized measure was found. 3.6. Radiation dose
3.4. Agreement analysis Mean DLP was 201.1 ± 22.7 mGy*cm and mean ED was 3.0 ± 0.2 mSv.
The inter-observer agreement for the evaluation of the aortic annulus measurements was excellent k = 0.902. The inter-observer agreement for the image quality of the coronary artery was k = 0.897. The inter-observer agreement for the evaluation, in the coronary artery, of the stenosis presence and the stenosis degree were k = 0.852 and k = 0.817, respectively.
3.7. Impact of coronary calcium score on image quality and diagnostic performance of coronary CT In 108 patients, without stents or CABGs, CCS evaluation was performed. Based on CCS, 41/108 (38.0 %) patients had a value < 400, 67/108 (62.0 %) patients had a value ≥400. Image quality findings according to CCS is given in Table 6. In the group with CCS < 400, CT had better diagnostic performance compared to the group with
3.5. TAVI procedure outcome Procedural success was 100 % without intraoperative mortality. A moderate paravalvular regurgitation occurred in 4/223 patients (1.8 %) 2 days after valve implantation. A significant direct correlation was 4
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Fig. 2. Aorta, peripheral accesses and coronary arteries evaluation in a 76-year-old male patient undergoing 192 × 2-DSCT for TAVI planning. Curved planned reconstructions provide aorta (A–B) and iliac-femoral arteries (C–D) assessment. Volume rendering (E) allows evaluating aorta and iliac-femoral arteries conformation necessary for surgical treatment. Image quality value was high (score 4) and curved planar reconstruction allows to evaluate coronary stenosis and stents patency in the right coronary artery (F), in the left anterior descending (G) and in the circumflex artery (H).
5
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patients could be safely excluded with CT imaging. Because non-diagnostic CT examinations typically lead to ICA in clinical practice, we performed an intention-to-diagnose analysis in which non-diagnostic images were considered as positive for stenosis ≥50 % and ≥70 %. This approach estimates the diagnostic accuracy of CT more conservatively than an analysis that excludes non-diagnostic vessels; however, the diagnostic accuracies for stenosis ≥50 % and ≥70 % were high, on a per-segment analysis 89.6 % and 84.8 %, and on a perpatient analysis 90.6 % and 87.0 %, respectively. The lower specificity and PPV would be due to not only for heavy calcification but also for motion artefacts secondary to increased heart rate, arrhythmia and incomplete breath holding. Pre-procedural evaluation of ISR and CABGs patency is of crucial importance to stratify patient risk and to determine whether myocardial revascularization is indicated before TAVI, and previous studies have demonstrated the high CT accuracy to evaluate stents and CABGs patency [21,22]. Our study included 78 patients with stents and 37 with CABGs. The CT evaluation of ISR, on a patient-based analysis, resulted in high NPV (94.7 %) but lower PPV (62.5 %) with an overall evaluability of 85.2 %. Moreover, NPV for CABGs stenosis assessment, on a patient-based analysis, was high 94.1 %, with overall evaluability of 100 %. Our results regarding specificity should be related also to the use of a last generation iterative reconstruction algorithm (ADMIRE, Siemens Healthineers) which was shown to improve the specificity of cardiac CT in calcified vessels [23,24]. The 192 × 2 DSCT scanner, with ultra-high pitch (3.2) and 0.22″ of resolution time, allowed to scan the whole heart volume during one heartbeat, reducing the potential artefacts related to movement, even in case of patients with arrhythmic hearth rate (n = 44). Moreover, the same technology allowed performing the examinations with a contrast injection flow rate of 5 ml/s maintaining an optimal vessel attenuation for both coronary tree and thoracic-abdominal aorta. Ultra-high pitch spiral acquisition allowed to cover the entire aorta and ilio-femoral vessels within less than 2″ and to obtain very high vascular attenuation. In the previous study, the optimal vascular attenuation for stenosis detection in coronary CT angiography was thought to be approximately 350–400 HU [25–27]. Therefore, our study would have sufficiently good CT attenuation to evaluate all arteries. In the SCCT guidelines [17], imaging of the AoA in systole is said to be preferable over diastole because of the dynamic changes of the annulus and slightly larger annular sizes noted in systole. On the other hand, coronary evaluation in mid-diastole is considered to be preferable over systole [28]. In this study, using a standardized protocol, all exams were acquired in systolic phase, which remains constant even in increased or arrhythmic hearth rate. This specification allowed reducing motion artefacts that may lead to a significant impairment in CT evaluability of coronary arteries, as underlines in this previous work [29]. Furthermore, computer-aided software with an expert radiologist intervention allowed to estimate correctly AoA area (r = 0.98, p < 0.001) with quick reading time, as demonstrated in other previous study [30]. The amount of coronary calcification quantified by the CCS was undoubtedly the strongest influencing factor on diagnostic image quality in CT [15,16]. Ocks et al. [31], using a DSCT scanner with an ultra-high pitch value, affirmed that coronary CT with minimal radiation exposure is most appropriate in patients with CCS ≤ 600. The diagnostic CT performance in their study dropped with a high CCS value. Moreover, in our study, as in the previous work of Ocks et al. [31], arrhythmia or heart rate ≥65 bpm not influenced the CT diagnostic performance. Ismail TF et al. [32] concluded that the high-pitch protocol significant reduces radiation and contrast doses and is non-inferior to standard-pitch acquisitions for aortic assessment; but if coronary assessment is critical, this should be followed by a conventional standardpitch acquisition. However, it is important to underline that, differently to us, they used a second-generation DSCT, the scan range started very high and the acquisition was in diastolic phase.
Table 3 Overall mean quantitative parameters for coronary artery. Vessels
Mean HU
Right coronary artery Left main coronary artery Left circumflex artery Left anterior descending artery
516.9 517.8 512.1 497.5
± ± ± ±
Mean CNR 32.4 39.6 43.7 51.9
13.9 17.2 14.4 15.7
± ± ± ±
2.6 4.1 3.8 3.9
Table 4 Diagnostic performance of pre-TAVI CT vs invasive coronary angiography using a cut-off value ≥ 50 % and ≥ 70 % of stenosis. Se (%)
Sp (%)
PPV (%)
NPV (%)
DA (%)
Segmentbased
97.6 (604/619)
Patientbased
97.8 (44/45)
87.6 (2389/ 2726) 88.8 (158/ 178)
64.2 (604/ 941) 68.8 (44/64)
99.0 (2389/ 2404) 99.4 (158/ 159)
89.6 (2993/ 3345) 90.6 (202/ 223)
Segmentbased
88.5 (577/652)
Patientbased
92.5 (37/40)
83.8 (2258/ 2693) 85.8 (157/ 183)
54.7 (577/ 1012) 58.7 (37/63)
96.8 (2258/ 2693) 98.1 (157/ 160)
84.8 (2835/ 3345) 87.0 (194/ 223)
≥50 %
≥ 70%
Abbreviations. – Se: sensitivity; Sp: specificity; PPV: positive predictive value; NPV: negative predictive value; DA: diagnostic accuracy.
CCS ≥400. Moreover, in the group with CCS < 600, CT had better diagnostic performance compared to the group with CCS ≥ 600. The CT diagnostic performance with the threshold values ≥50 % and ≥70 % are given in Tables 7a and b and 8 a and b, respectively. The impact of arrhythmia and heart rate ≥65 bpm on diagnostic accuracy did not reach statistical significance. On segment-based analysis, the diagnostic accuracy with the threshold values ≥ 50 % were 92.6 % (with regular or heart rate < 65 bpm) and 86.9 % (with arrhythmic or heart rate ≥ 65 bpm) (p = 0.102). On segment-based analysis, the diagnostic accuracy with the threshold values ≥70 % were 86.1 % (with regular or heart rate < 65 bpm) and 83.2 % (with arrhythmic or heart rate ≥65 bpm) (p = 0.08).
4. Discussion TAVI is the standard treatment of aortic valve stenosis in patients with an intermediate to high surgical risk and CT represents the reference method for the AoA sizing and peripheral accesses assessment [7]. Pre-procedural screening for CAD with ICA is highly recommended, but only one third are therapeutics [4,5]. Due to age and comorbidities, heavy coronary calcifications may be common and challenge the diagnostic performance of coronary CT [15,16]. The aim of this study is to evaluate the feasibility, the image quality and the diagnostic performance of third generation DSCT with ultra-high pitch protocol for TAVI planning and coronary tree assessment and the impact of coronary calcifications on the diagnostic performance. In this study, we obtain an overall mean attenuation value > 400 HU in all vascular segments with very good reliability for prosthesis sizing (100 % procedural success rate). Considering ICA as the gold standard, we found that CT imaging for obstructive CAD ≥ 50 % had high sensitivity and NPV on a per-segment analysis, 97.6 % and 99.0 % respectively, and on a per-patient analysis, 97.8 % and 99.4 %, respectively. We also found that CT imaging for obstructive CAD ≥ 70 % had high sensitivity and NPV, on a per-segment analysis, 88.5 % and 96.8 % respectively and, on a per-patient analysis, 92.5 % and 98.1 %, respectively. These results suggest that obstructive CAD in TAVI 6
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Fig. 3. Coronary arteries evaluation in a 78-year-old female patient undergoing 192 × 2-DSCT for TAVI planning. Comparison between ICA (A) and CT curved planar reformation (B), axial (C), sagittal (D). The figure shows a diameter stenosis between 50–60 % and area obstruction between 80–90 % in LAD artery (white arrows), correctly evaluate with CT examination.
stratified the CT diagnostic performance using the same CCS threshold than in our study (low < 400, high ≥400), and they obtained a CT performance slightly lower than us concluding that in patients with CCS ≥ 400 CT performed less well. We hypothesize that these results should be mainly relate to the presence of beam hardening artifacts. In the most recent work, Annoni AD et al. [40], using a third generation 256-slices CT scanner, obtained sensitivity, specificity, PPV, NPV and diagnostic accuracy similar to us in the detection of coronary stenosis ≥50 % and ≥70 %, in the detection of ISR and in the CABGs stenosis. Unlike us, they used a retrospective ECG-gated acquisition to assess the heart and the thoracic aorta and a subsequent non–gated spiral scan to assess the abdominal aorta and iliac-femoral arteries and
Several previous studies [33–40] have looked to evaluate the diagnostic performance of coronary tree assessment in CT before TAVI planning and concluded that CT is a useful test to rule out significant obstructive CAD and to evaluate stents and CABGs patency. To the best of our knowledge, the present study is the work with the largest simple size and a prospective design with this aim and the only one that used a single prospective ECG-gated ultra-high pitch acquisition for aorta, iliac vessels and coronary artery assessments. Harris et al. [37] and Matsumoto et al. [38], obtained a mean CCS, respectively, similar than us, but they did not stratified the CT diagnostic performance based on CCS values. Rossi et al. [39] using a second generation DSCT with a retrospective ECG-gated protocol, 7
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Table 5 Diagnostic performance of pre-TAVI CT vs invasive coronary angiography in the assessment of intra stent re-stenosis and coronary artery bypass grafts stenosis. Se (%)
Sp (%)
PPV (%)
NPV (%)
DA (%)
92.6 (25/27) 83.3 (25/30)
70.6 (15/36) 70.6 (60/85)
62.5 (25/40) 50.0 (25/50)
94.7 (36/38) 92.3 (60/65)
78.2 (61/78) 73.9 (85/115)
95.0 (19/20) 93.3 (28/30)
94.1 (16/17) 85.7 (18/21)
95.0 (19/20) 90.3 (28/31)
94.1 (16/17) 90.0 (18/20)
94.6 (35/37) 90.2 (46/51)
Stents Number of patients
78
Patient-based
Number of stents
115
Vessel-based
Number of patients
37
Patient-based
Number of CABGs
51
Vessel-based
CABGs
Abbreviations. – Se: sensitivity; Sp: specificity; PPV: positive predictive value; NPV: negative predictive value; DA: diagnostic accuracy; CABG: coronary angiography by-pass graft. Table 6 Image quality according to Agatston coronary calcium scoring on segmentbased analysis. Threshold
Mean Agatston CCS
1
2
3
4
p value
< 400 (38.0 %) ≥400 (62.0 %)
141.2 ± 56.3 (47.2–234.9) 1099.2 ± 498.2 (625.1–2212.2)
3.2 %
18.5 %
16.1 %
62.2 %
p < 0.001
6.0 %
30.8 %
25.3 %
37.9 %
Table 8 Diagnostic performance of pre-TAVI CT vs invasive coronary angiography using a cut-off value ≥ 70 % of stenosis in two CCS groups. a
Segment-based Patient-based
Abbreviations. – CCS: coronary calcium scoring.
Segment-based
a
Segment-based Patient-based
Se (%)
Sp (%)
PPV (%)
NPV (%)
DA (%)
< 400 ≥400 < 400 ≥400
93.7 98.5 93.1 98.1
93.3 65.1 92.1 79.6
62.9 66.1 67.2 73.3
99.4 97.7 99.7 98.1
95.6 83.6 96.1 86.1
Patient-based
Segment-based Patient-based
Se (%)
Sp (%)
PPV (%)
NPV (%)
DA (%)
< 600 ≥600 < 600 ≥600
91.7 99.0 90.1 97.1
95.3 62.1 94.1 65.6
61.3 67.5 67.2 78.4
99.2 95.1 99.7 92.1
97.1 80.7 97.0 83.2
Sp (%)
PPV (%)
NPV (%)
DA (%)
≤400 > 400 ≤400 > 400
74.3 89.3 77.1 93.1
87.5 67.6 91.1 73.2
63.9 52.1 66.1 54.9
97.0 92.1 98.4 95.9
91.6 82.3 94.6 82.6
CCS
Se (%)
Sp (%)
PPV (%)
NPV (%)
DA (%)
≤600 > 600 ≤600 > 600
71.6 90.5 75.3 94.8
89.3 60.6 91.9 62.3
66.8 50.3 67.8 54.4
98.1 90.6 99.3 92.3
92.5 80.0 95.2 84.6
% % % %
% % % %
% % % %
% % % %
% % % %
% % % %
% % % %
% % % %
% % % %
% % % %
Abbreviations. – Se: sensitivity; Sp: specificity; PPV: positive predictive value; NPV: negative predictive value; DA: diagnostic accuracy.
of CAD in patients with aortic stenosis was 40–75 % [33–40], and the prevalence of CAD in our study was within the range. Second, images were acquired using a prospective ECG-gated protocol on a third generation DSCT scanner. However, the rapidly diffusion of CT scanner technology may soon overcome this limitation. In conclusion, our study revealed that using ultra-high pitch protocol with DSCT provides accurate information and very good image quality of both aorta and coronary tree with a high NPV for obstructive CAD. In patients with severe coronary calcifications, CT performed less well. Because CT is increasingly used for TAVI planning, these findings support the use of CT, helping to avoid unnecessary ICA. This would provide multiple health and cost benefits, thus reducing further radiation, amount of contrast dose, and hospitalization costs, as well as the potential risks related to invasive procedures.
b CCS
Se (%)
b
Table 7 Diagnostic performance of pre-TAVI CT vs invasive coronary angiography using a cut-off value ≥ 50 % of stenosis in two CCS groups.
CCS
CCS
Abbreviations. – CCS: coronary calcium scoring; Se: sensitivity; Sp: specificity; PPV: positive predictive value; NPV: negative predictive value; DA: diagnostic accuracy.
they did not considered the CCS. Finally, although radiation dose is not the topic of this work, with ultra-high pitch, mean ED is resulted 3.0 mSv. Radiation dose comparison between different CT protocols in TAVI planning could be a research field for further studies. Indeed, despite the radiation dose is not considered an issue because the high percentage are elderly patients, with the use of ultra-high pitch is possible to obtain, at any heart rate, an accurate coronary evaluation in TAVI planning, avoiding the use of a retrospective protocol, and following the “as low as reasonably achievable” radiation safety principle, based on the minimization of radiation doses and limiting the release of radioactive materials into the environment. Moreover, if the acquisition is not diagnostic, a following retrospective protocol for coronary assessment could be performed. There are some limitations in our study. First, PPV and NPV of CT coronary might be changed according to the prevalence of the study population. However, the previous study reported that the prevalence
Ethical standards All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/ or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study.
Disclosure The authors have no disclosure. 8
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Funding
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This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Declaration of Competing Interest The authors declared no potential conflicts of interests associated with this study. Acknowledgments None. References [1] C. Mantini, G. Di Giammarco, J. Pizzicannella, et al., Grading of aortic stenosis severity: a head-to-head comparison between cardiac magnetic resonance imaging and echocardiography, Radiol. Med. 123 (9) (2018) 643–654. [2] F. Hecker, M. Arsalan, W.K. Kim, et al., Transcatheter aortic valve implantation (TAVI) in 2018: recent advances and future development, Minerva Cardioangiol. 66 (3) (2018) 314–328. [3] R.L. Osnabrugge, S.V. Arnold, M.R. Reynolds, et al., Health status after transcatheter aortic valve replacement in patients at extreme surgical risk: results from the CoreValve U.S. Trial, JACC Cardiovasc. Interv. 8 (2015) 315–323. [4] C.M. Otto, D.J. Kumbhani, K.P. Alexander, et al., ACC expert consensus decision pathway for transcatheter aortic valve replacement in the management of adults with aortic stenosis: a report of the American College of Cardiology Task Force on Clinical Expert Consensus Documents, J. Am. Coll. Cardiol. 69 (2017) 1313–1346. [5] H. Baumgartner, V. Falk, J.J. Bax, et al., ESC/EACTS guidelines for the management of valvular heart disease, Eur. Heart J. 38 (2017) 2739–2786. [6] B. Ibanez, S. James, S. Agewall, et al., ESC Guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation: the task force for the management of acute myocardial infarction in patients presenting with ST-segment elevation of the European Society of Cardiology (ESC), Eur. Heart J. 39 (2018) 119–177. [7] J.T. Tretter, S. Mori, R.H. Anderson, et al., Anatomical predictors of conduction damage after transcatheter implantation of the aortic valve, Open Heart 6 (1) (2019) e000972. [8] R. Haase, P. Schlattmann, P. Gueret, et al., Diagnosis of obstructive coronary artery disease using computed tomography angiography in patients with stable chest pain depending on clinical probability and in clinically important subgroups: metaanalysis of individual patient data, BMJ 365 (2019) l1945. [9] C.F. Jia, J. Zhong, X.Y. Meng, et al., Image quality and diagnostic value of ultra lowvoltage, ultra low-contrast coronary CT angiography, Eur. Radiol. 29 (7) (2019) 3678–3685. [10] G. Apfaltrer, D.H. Szolar, E. Wurzinger, et al., Impact on image quality and radiation dose of third-generation dual-source computed tomography of the coronary arteries, Am. J. Cardiol. 119 (8) (2017) 1156–1161. [11] P. Dankerl, M. Hammon, H. Seuss, et al., Computer-aided evaluation of low-dose and low-contrast agent third-generation dual-source CT angiography prior to transcatheter aortic valve implantation (TAVI), Int. J. Comput. Assist. Radiol. Surg. 12 (5) (2017) 795–802. [12] B. Horehledova, C. Mihl, C. Schwemmer, et al., Aortic root evaluation prior to transcatheter aortic valve implantation-Correlation of manual and semi-automatic measurements, PLoS One 13 (6) (2018) e0199732. [13] D.O. Bittner, M. Arnold, L. Klinghammer, et al., Contrast volume reduction using third generation dual source computed tomography for the evaluation of patients prior to transcatheter aortic valve implantation, Eur. Radiol. 26 (12) (2016) 4497–4504. [14] C.R. Talei Franzesi, D. Ippolito, L. Riva, et al., Diagnostic value of iterative reconstruction algorithm in low kV CT angiography (CTA) with low contrast medium volume for transcatheter aortic valve implantation (TAVI) planning: image quality and radiation dose exposure, Br. J. Radiol. 91 (1092) (2018) 20170802. [15] M. Kruk, D. Noll, S. Achenbach, et al., Impact of coronary artery calcium characteristics on accuracy of CT angiography, JACC Cardiovasc. Imaging 7 (2014) 49–58. [16] R.T. Yan, J.M. Miller, C.E. Rochitte, et al., Predictors of inaccurate coronary arterial stenosis assessment by CT angiography, JACC Cardiovasc. Imaging 6 (2013) 963–972. [17] S. Achenbach, V. Delgado, J. Hausleiter, et al., SCCT expert consensus document on computed tomography imaging before transcatheter aortic valve implantation (TAVI)/ transcatheter aortic valve replacement (TAVR), J. Cardiovasc. Comput. Tomogr. 6 (2012) 366–380. [18] H. Alkadhi, H. Scheffel, L. Desbiolles, et al., Dual-source computed tomography coronary angiography: influence of obesity, calcium load, and heart rate on
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European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
Research article
Third generation dual source CT with ultra-high pitch protocol for TAVI planning and coronary tree assessment: feasibility, image quality and diagnostic performance
T
Nicolò Schicchia, Marco Fogantea,*, Paolo Esposto Pirania, Giacomo Agliataa, Tommaso Pivab, Corrado Tagliatia, Matteo Marcuccia, Antonio Franciosoa, Andrea Giovagnonia a b
Radiology Department, Azienda Ospedaliero Universitaria “Ospedali Riuniti”, 60126, Ancona, Italy Cardiologic Department, Azienda Ospedaliero Universitaria “Ospedali Riuniti”, 60126, Ancona, Italy
A R T I C LE I N FO
A B S T R A C T
Keywords: DSCT TAVI Coronary calcium scoring Coronary assessment Aortic valve
Purpose: To evaluate the feasibility, image quality (IQ) and diagnostic performance of third generation 192 × 2 dual source computer tomography (DSCT) with ultra-high pitch acquisition for trans-catheter aortic valve implantation (TAVI) planning and coronary tree assessment. Method: In this prospective study, 223 patients underwent to DSCT for TAVI. Coronary calcium scoring (CCS) was calculated. Attenuation values were measured at aortic levels, femoral and coronary arteries. IQ was evaluate with a 4-point scale. The CT performance, in the assessment of coronary stenosis ≥50 % and ≥70 %, was compared with invasive coronary angiography (ICA), served as reference standard. Aortic annulus (AoA) CT derived area and implanted prosthesis size were correlate with Spearman’s test. Results: Attenuation values > 400HU were obtain in all segments. IQ median value was ≥ 3. In the assessment of stenosis ≥50 %, on a segment-based analysis, CT sensitivity, specificity, positive and negative predictive values and diagnostic accuracy were 97.6 %, 87.6 %, 64.2 %, 99.0 % and 89.6 %, on patient-based analysis were 97.8 %, 88.8 %, 68.8 %, 99.4 % and 90.6 %, respectively. In the assessment of stenosis ≥70 %, on segmentbased analysis, were 88.5 %, 83.8 %, 54.7 %, 96.8 % and 84.8 %, and on patient-based analysis were 92.5 %, 85.8 %, 58.7 %, 98.1 % and 87.0 %, respectively. The CT performed better in the group with lower CCS. A direct correlation was found between AoA CT derived area and prosthesis size. Conclusion: DSCT, using a single prospective ECG-triggered ultra-high pitch acquisition, is feasible for TAVI planning and in the assessment of coronary stenosis. CT performed worse in patients with severe coronary calcifications.
1. Introduction Aortic stenosis is the most prevalent valve heart disease in developed western countries [1]. Trans-catheter aortic valve implantation (TAVI) is a safe treatment for patients with severe symptomatic aortic stenosis [2,3]. Invasive coronary angiography (ICA) is recommended for pre-procedural TAVI due to possible harmful of coronary artery stenosis on procedural outcome and prognosis if left untreated. However, only one third of all ICAs are performed with a revascularization procedure, while the rest only for diagnostic purpose [4,5]. Moreover, ICA is not ideal as a widespread diagnostic procedure, due partly to its high cost, but mostly because of the associated mortality and morbidity [6].
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Computed tomography (CT) is part of the routine TAVI planning for sizing the valve prosthesis and assessment of the access route [7]. Moreover, CT is used to rule out significant coronary stenosis with low to intermediate pre-test probability for coronary artery disease (CAD) [8]. A holistic CT evaluation of aorta, peripheral vessels and coronary arteries pre-TAVI procedure could lead to a reduction of unnecessary ICA and, consequently, of cumulative radiation dose, contrast volume and risk management. The introduction of third generation dual source (DS) CT scanners provided a new ultra-high pitch protocol with very low acquisition time, that allows reducing any motion artefacts [9,10]. In recent studies, the use of third generation DSCT with ultra-high pitch protocol for TAVI planning have demonstrated excellent results, but no one
Corresponding author. E-mail address: [email protected] (M. Fogante).
https://doi.org/10.1016/j.ejrad.2019.108749 Received 3 August 2019; Received in revised form 7 November 2019; Accepted 12 November 2019 0720-048X/ © 2019 Elsevier B.V. All rights reserved.
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performed: a small (200 mm) and large (300 mm) field of view data set for the assessment of the aortic root and coronary tree (cardiac reconstruction) and the ilio-femoral accesses (vascular reconstruction), respectively.
included coronary tree assessment [11–14]. Furthermore, due to age and comorbidities, heavy coronary calcifications and high coronary calcium scoring (CCS) challenge the diagnostic performance of CT [15,16]. The aim of this study is to evaluate the feasibility, the image quality and the diagnostic performance of third generation DSCT with ultrahigh pitch protocol for TAVI planning and coronary tree assessment and the impact of CCS on the diagnostic performance.
2.3. Aortic annulus measurements and contrast attenuation evaluation For aortic annulus (AoA) measurements, the CT data sets were analysed using a computer-aided evaluation software (syngo.via, version VB10A; Siemens Healthcare, Erlangen, Germany) with clinical application “CT TAVI Planning”. Detailed measures of the aortic root anatomy focused on AoA dimensions, such as minimum and maximum diameters, area and the distance from the AoA to the coronary ostia were evaluated by two expert radiologist (both with ≥10 years of clinical experience in coronary CT angiography performance and analysis), as recommended by the SCCT expert consensus document [17]. For any disagreement in CT data analysis between the two readers, consensus was achieved. For each patient, contrast attenuation value, expressed as HU, and the corresponding standard deviation (SD), as indicator for image noise, were measured by one expert radiologist (with ≥10 years of clinical experience in coronary CT angiography performance and analysis) with ROIs placed on axial images at three different levels of the aorta (aortic root, descending thoracic aorta, sub-renal abdominal aorta) and middle third of the right and left common femoral arteries. Additional circular ROIs were placed into the right lobe of the liver with no vascular structures to calculate the contrast-to-noise ratio (CNR), as follow:
2. Material and methods 2.1. Study population The Institutional Review Board of our Hospital approved the study protocol. Written informed consent was obtained from all patients. In this prospective study, between April 2018 and April 2019, were included 236 consecutive patients, referred to our Hospital for CT and ICA for TAVI planning. In all patients, ICA was performed at least 3 days after CT. Exclusion criteria were: severe adverse reactions to an iodinated contrast agent (n = 5), and estimated glomerular filtration rate < 30 ml/min/1.73m2 (n = 8). Final study cohort was composed by 223 patients. 2.2. CT protocol All CT examinations were performed using a 384(192 × 2)-slices third generation DSCT scanner (SOMATOM Force CT; Siemens Healthineers, Forchheim, Germany) with patients in supine position and feet towards the gantry. A 20-gauce cannula was inserted into superficial vein of the right antecubital fossa, connected to a two-way injector (EmpowerCTA®+ Injector System; Bracco Injeneering, Lausanne, Switzerland). No premedication with beta-blockers or nitrates was added before CT acquisition. All patients were examined with the same standardized examination protocol. First, a non-contrastenhanced prospective electrocardiogram (ECG) -triggered scan was acquired with a tube voltage of 120 kV and scan range from carina to diaphragmatic level, in patients without stents or coronary artery bypass graft. Then, a contrast-enhanced scan was acquired. All patients received 60 ml of contrast medium (Iomeprol, 400 mgI/ml; Bracco Imaging, Milan, Italy) at flow rate of 5 ml/s followed by 50 ml of saline solution at 4.8 ml/s. Scan parameters are summarized in Table 1. Scan protocol consisted in a single prospective ECG-gated ultra-high pitch (pitch factor, 3.2) acquisition. Acquisition started when region of interest (ROI) value at the aortic diaphragmatic level reached 240 Hounsfield Unit (HU). Coronary arteries images were acquired at 30 % of R-peak-to-R-peak. For each patient, two reconstructions were
CNR = (vessel attenuation – liver attenuation) / image noise
2.4. Coronary calcium scoring and coronary arteries assessment The CCS was calculated, by one expert radiologist (with ≥ 10 years of clinical experience in coronary CT angiography performance and analysis) as previously described [18], using a dedicated computeraided evaluation software (syngo.via, version VB10A; Siemens Healthcare, Erlangen, Germany) with clinical application “Cardiac Calcium Scoring”; instead, for coronary arteries assessment was used the clinical application “CT Cardiac”. The image quality and the presence and the degree of coronary stenosis were evaluated by two radiologists (both with ≥ 10 years of clinical experience in coronary CT angiography performance and analysis). Coronary arteries were segmented as suggested by the American Heart Association [19]. To evaluate semi-qualitative image quality score for each native coronary artery, stent, and CABG was used a 4-point Likert image
Table 1 Contrast-enhanced CT scan parameters. Acquisition parameters Scan technique Scan direction (from – to) Scan interval (from – to) Gantry rotation time (s) Pitch factor Tube voltage Tube current
Bolus tracking Cranio – caudal Lung apexes – ischium 0.22 3.2 Automatic modulation (CARE kV, Siemens Healthineers) Automatic modulation (CARE kV, Siemens Healthineers)
Slice thickness – Slice increment (mm) Kernel Iterative reconstruction algorithm Slice thickness – Slice increment (mm) Kernel Iterative reconstruction algorithm
0.6 – 0.4 Bobyvascular 40 ADMIRE (Siemens Healthcare) – strength 4 1 – 0.7 Bodyvascular 44 ADMIRE (Siemens Healthcare) – strength 3
Reconstruction parameters Cardiac reconstruction
Vascular reconstruction
Abbreviations. – ADMIRE: advanced modeled iterative reconstruction. 2
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calculated. The CT diagnostic performance per-segment and per-patient analysis in the assessment of coronary stenosis ≥50 % and ≥70 % was determined against the reference standard ICA.Chi-square test was used to compare semi-qualitative image quality of coronary arteries in two subgroups with CCS < 400 and ≥400. The CT diagnostic performance per-segment and per-patient analysis in the assessment of coronary stenosis ≥50 % and ≥70 % was determined against the reference standard ICA in subgroups with CCS < 400 and ≥400 and in subgroups with CCS < 600 and ≥600. The Cohen’s Kappa test (k) was used to evaluate the inter-observer agreement. The Spearman’s correlation test (r) was used to correlate AoA CT derived area with implanted prosthesis size. Mean DLP and ED values were calculated. A p value < 0.05 was considered statistically significant.
quality score: 1 poor/not diagnostic: impaired image quality limited by excessive noise or poor vessel wall definition; 2 adequate: reduced image quality either poor vessel wall definition or excessive image noise; 3 good: effect of image noise, limitations of low contrast resolution, and vessel margin definition are minimal; 4 excellent: excellent attenuation of the vessel lumen and clear delineation of vessel walls. For each patient, contrast attenuation value, expressed as HU, and the corresponding SD, as indicator for image noise, were measured by ROIs placed in the proximal tract of each coronary arteries. Additional circular ROIs were placed into the surrounding tissue of the aortic root immediately cranial to the left main coronary artery to calculate the noise ratio CNR, as follow:
3. Results 3.1. Study population characteristics
CNR = (coronary attenuation – surrounding tissue) / image noise.
The mean age was 79.2 ± 4.9 years. Mean heart rate during examinations was 66.2 ± 9.8 beats per minute. 44/223 (19.7 %) patients had arrhythmic or high heart rate, ≥65 beats per minute (bpm). Mean CT scan time was 1.95 ± 0.12 s [0.96–2.5 s]. The mean CCS was 733.1 ± 375.6 (299.4–1810.8). Patients with stent were 78 and with CABGs were 37. Total stents were 115 and total CABGs were 51.
Curved planar reformation images were used to rule out in all the native coronary arteries the presence of stenosis ≥50 % and ≥70 %. Moreover, all the stented segments were evaluated for the presence of significant intra stent restenosis (ISR) (defined as a lumen diameter reduction more than 50 %) and by-pass grafts stenosis with softwareaid evaluation. Results were also reported in subgroups of patients defined by CCS < 400 and ≥400 and in subgroups of patients defined by CCS < 600 and ≥600.
3.2. Aortic annulus measurements and contrast attenuation values Mean minimum diameter of the AoA was 19.4 ± 1.8 mm (range, 17–26 mm); mean maximum diameter was 27.9 ± 2.9 mm (range, 22–32 mm) and mean area was 451.4 ± 76.4 mm2 (range, 306–656 mm2). Mean distance of the AoA plane to the left coronary ostium was 14.1 ± 2.8 mm (range, 9–19 mm) and to the right coronary ostium was 16.7 ± 4.7 mm (range, 11–31 mm). The overall mean attenuation values and CNRs of aortic segments and common iliac arteries were > 500 HU and < 20, respectively (Table 2). CT imaging examples of AoA and vessels evaluation are shown in Figs. 1 and 2.
2.5. Invasive coronary angiography All patients included in our study underwent ICA within 1 month before the TAVI procedure. ICA procedures were performed with standard technique by two operators with more than 15 years of clinical experience blinded to CT results. Angiograms were examined using a quantitative coronary angiography software (QantCor, QCA; Pie Medical Imaging, Maastricht, Netherlands).
3.3. Coronary arteries assessment
2.6. TAVI procedure outcome
Mean contrast attenuation values and CNR values of the coronary arteries are summarized in Table 3. 3179 coronary segments on 3345 (95.0 %) were considered as evaluable. In 166/3345 (5.0 %) segments the image quality score was poor/not-diagnostic because of large calcifications (125 segments) and motion artefacts due to incomplete breath holding/movements (41 segments). CT demonstrated an overall evaluability of ISR and CABGs stenosis of 85.2 % and 100.0 %, respectively. Semi-qualitative image quality median values for coronary arteries were ≥3. The patients with stenosis ≥50 % and ≥70 % were 45 and 40, respectively. Table 4 shows CT sensitivity, specificity, PPV, NPV and diagnostic accuracy for assessment of stenosis ≥50 % and ≥70 % in comparison with ICA, considering poor/non-diagnostic images as positive for stenosis ≥50 % and ≥70 %. Fig. 3 shows an example of comparison between ICA and CT in coronary arteries assessment. Semi-qualitative image quality median values for stents and
TAVI procedure success was defined accordingly to correct device, annular rupture, evidence of prosthesis instability, and peri-procedural mortality. AoA CT derived area was compared with implanted prosthesis size. 2.7. Radiation dose The dose-length product (DLP) and the effective dose (ED) of each CT were evaluated. The ED was calculated as the DLP multiplied for a conversion coefficient for the chest k = 0.014 mSv/mGy*cm and for abdomen k = 0.015 mSv/mGy*cm. Because of the scan protocol including both thorax and abdomen, an average conversion factor k = 0.015 mSv/mGy*cm was used [20]. 2.8. Statistical analysis
Table 2 Overall mean quantitative parameters for aorta and peripheral accesses.
Statistical analysis was performed with the SPSS v.17.0 software (SPSS Inc; Chicago, IL). Continuous variables were expressed as mean ± SD, and discrete variables were expressed as absolute numbers and percentages. Mean minimum diameter, maximum diameter, area of the AoA, and the distance of the AoA to the coronary ostia were calculated. Mean attenuation and CNR in each vascular segment were calculated. Semiqualitative image quality of coronary arteries, stents and CABGs were 3
Vessel segment
Mean HU
Aortic root Descending aorta Subrenal aorta Right common femoral artery Left common femoral artery
521.1 537.8 545.2 553.5 548.1
± ± ± ± ±
Mean CNR 50.4 59.2 55.7 65.2 67.8
15.1 14.1 16.1 18.5 19.1
± ± ± ± ±
3.6 4.1 3.2 6.7 5.9
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Fig. 1. Aortic annulus evaluation in a 73-year-old female patient undergoing 192 × 2-DSCT for TAVI planning. The centre axis of left ventricle outflow tract and aortic root were chosen as reference with the 3 orthogonal planes. The longitudinal axis in coronal and sagittal views were aligned (A, B). The transverse plane was aligned at the lowest level of the valve until the hinge points of the aortic leaflets were depictable (C). Aortic annulus was defined as a virtual ring formed by joining the basal attachments of the aortic leaflets. Maximum diameter, minimum diameter, and area were measured at this level.
CABGs were ≥3. The patients with ISR were 27 and the patients with CABGs stenosis were 20. Table 5 shows, on a patient-based and vesselbased analysis, CT diagnostic performance in the assessment of ISR and CABGs stenosis, considering poor/non-diagnostic images as positive for ISR and CABGs stenosis.
found between CT derived area and implanted prosthesis size (r = 0.98, p < 0.001). In 7/223 patients (3.1 %) CT measurements were oversized, while in 9/223 patients (4.0 %) an undersized measure was found. 3.6. Radiation dose
3.4. Agreement analysis Mean DLP was 201.1 ± 22.7 mGy*cm and mean ED was 3.0 ± 0.2 mSv.
The inter-observer agreement for the evaluation of the aortic annulus measurements was excellent k = 0.902. The inter-observer agreement for the image quality of the coronary artery was k = 0.897. The inter-observer agreement for the evaluation, in the coronary artery, of the stenosis presence and the stenosis degree were k = 0.852 and k = 0.817, respectively.
3.7. Impact of coronary calcium score on image quality and diagnostic performance of coronary CT In 108 patients, without stents or CABGs, CCS evaluation was performed. Based on CCS, 41/108 (38.0 %) patients had a value < 400, 67/108 (62.0 %) patients had a value ≥400. Image quality findings according to CCS is given in Table 6. In the group with CCS < 400, CT had better diagnostic performance compared to the group with
3.5. TAVI procedure outcome Procedural success was 100 % without intraoperative mortality. A moderate paravalvular regurgitation occurred in 4/223 patients (1.8 %) 2 days after valve implantation. A significant direct correlation was 4
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Fig. 2. Aorta, peripheral accesses and coronary arteries evaluation in a 76-year-old male patient undergoing 192 × 2-DSCT for TAVI planning. Curved planned reconstructions provide aorta (A–B) and iliac-femoral arteries (C–D) assessment. Volume rendering (E) allows evaluating aorta and iliac-femoral arteries conformation necessary for surgical treatment. Image quality value was high (score 4) and curved planar reconstruction allows to evaluate coronary stenosis and stents patency in the right coronary artery (F), in the left anterior descending (G) and in the circumflex artery (H).
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patients could be safely excluded with CT imaging. Because non-diagnostic CT examinations typically lead to ICA in clinical practice, we performed an intention-to-diagnose analysis in which non-diagnostic images were considered as positive for stenosis ≥50 % and ≥70 %. This approach estimates the diagnostic accuracy of CT more conservatively than an analysis that excludes non-diagnostic vessels; however, the diagnostic accuracies for stenosis ≥50 % and ≥70 % were high, on a per-segment analysis 89.6 % and 84.8 %, and on a perpatient analysis 90.6 % and 87.0 %, respectively. The lower specificity and PPV would be due to not only for heavy calcification but also for motion artefacts secondary to increased heart rate, arrhythmia and incomplete breath holding. Pre-procedural evaluation of ISR and CABGs patency is of crucial importance to stratify patient risk and to determine whether myocardial revascularization is indicated before TAVI, and previous studies have demonstrated the high CT accuracy to evaluate stents and CABGs patency [21,22]. Our study included 78 patients with stents and 37 with CABGs. The CT evaluation of ISR, on a patient-based analysis, resulted in high NPV (94.7 %) but lower PPV (62.5 %) with an overall evaluability of 85.2 %. Moreover, NPV for CABGs stenosis assessment, on a patient-based analysis, was high 94.1 %, with overall evaluability of 100 %. Our results regarding specificity should be related also to the use of a last generation iterative reconstruction algorithm (ADMIRE, Siemens Healthineers) which was shown to improve the specificity of cardiac CT in calcified vessels [23,24]. The 192 × 2 DSCT scanner, with ultra-high pitch (3.2) and 0.22″ of resolution time, allowed to scan the whole heart volume during one heartbeat, reducing the potential artefacts related to movement, even in case of patients with arrhythmic hearth rate (n = 44). Moreover, the same technology allowed performing the examinations with a contrast injection flow rate of 5 ml/s maintaining an optimal vessel attenuation for both coronary tree and thoracic-abdominal aorta. Ultra-high pitch spiral acquisition allowed to cover the entire aorta and ilio-femoral vessels within less than 2″ and to obtain very high vascular attenuation. In the previous study, the optimal vascular attenuation for stenosis detection in coronary CT angiography was thought to be approximately 350–400 HU [25–27]. Therefore, our study would have sufficiently good CT attenuation to evaluate all arteries. In the SCCT guidelines [17], imaging of the AoA in systole is said to be preferable over diastole because of the dynamic changes of the annulus and slightly larger annular sizes noted in systole. On the other hand, coronary evaluation in mid-diastole is considered to be preferable over systole [28]. In this study, using a standardized protocol, all exams were acquired in systolic phase, which remains constant even in increased or arrhythmic hearth rate. This specification allowed reducing motion artefacts that may lead to a significant impairment in CT evaluability of coronary arteries, as underlines in this previous work [29]. Furthermore, computer-aided software with an expert radiologist intervention allowed to estimate correctly AoA area (r = 0.98, p < 0.001) with quick reading time, as demonstrated in other previous study [30]. The amount of coronary calcification quantified by the CCS was undoubtedly the strongest influencing factor on diagnostic image quality in CT [15,16]. Ocks et al. [31], using a DSCT scanner with an ultra-high pitch value, affirmed that coronary CT with minimal radiation exposure is most appropriate in patients with CCS ≤ 600. The diagnostic CT performance in their study dropped with a high CCS value. Moreover, in our study, as in the previous work of Ocks et al. [31], arrhythmia or heart rate ≥65 bpm not influenced the CT diagnostic performance. Ismail TF et al. [32] concluded that the high-pitch protocol significant reduces radiation and contrast doses and is non-inferior to standard-pitch acquisitions for aortic assessment; but if coronary assessment is critical, this should be followed by a conventional standardpitch acquisition. However, it is important to underline that, differently to us, they used a second-generation DSCT, the scan range started very high and the acquisition was in diastolic phase.
Table 3 Overall mean quantitative parameters for coronary artery. Vessels
Mean HU
Right coronary artery Left main coronary artery Left circumflex artery Left anterior descending artery
516.9 517.8 512.1 497.5
± ± ± ±
Mean CNR 32.4 39.6 43.7 51.9
13.9 17.2 14.4 15.7
± ± ± ±
2.6 4.1 3.8 3.9
Table 4 Diagnostic performance of pre-TAVI CT vs invasive coronary angiography using a cut-off value ≥ 50 % and ≥ 70 % of stenosis. Se (%)
Sp (%)
PPV (%)
NPV (%)
DA (%)
Segmentbased
97.6 (604/619)
Patientbased
97.8 (44/45)
87.6 (2389/ 2726) 88.8 (158/ 178)
64.2 (604/ 941) 68.8 (44/64)
99.0 (2389/ 2404) 99.4 (158/ 159)
89.6 (2993/ 3345) 90.6 (202/ 223)
Segmentbased
88.5 (577/652)
Patientbased
92.5 (37/40)
83.8 (2258/ 2693) 85.8 (157/ 183)
54.7 (577/ 1012) 58.7 (37/63)
96.8 (2258/ 2693) 98.1 (157/ 160)
84.8 (2835/ 3345) 87.0 (194/ 223)
≥50 %
≥ 70%
Abbreviations. – Se: sensitivity; Sp: specificity; PPV: positive predictive value; NPV: negative predictive value; DA: diagnostic accuracy.
CCS ≥400. Moreover, in the group with CCS < 600, CT had better diagnostic performance compared to the group with CCS ≥ 600. The CT diagnostic performance with the threshold values ≥50 % and ≥70 % are given in Tables 7a and b and 8 a and b, respectively. The impact of arrhythmia and heart rate ≥65 bpm on diagnostic accuracy did not reach statistical significance. On segment-based analysis, the diagnostic accuracy with the threshold values ≥ 50 % were 92.6 % (with regular or heart rate < 65 bpm) and 86.9 % (with arrhythmic or heart rate ≥ 65 bpm) (p = 0.102). On segment-based analysis, the diagnostic accuracy with the threshold values ≥70 % were 86.1 % (with regular or heart rate < 65 bpm) and 83.2 % (with arrhythmic or heart rate ≥65 bpm) (p = 0.08).
4. Discussion TAVI is the standard treatment of aortic valve stenosis in patients with an intermediate to high surgical risk and CT represents the reference method for the AoA sizing and peripheral accesses assessment [7]. Pre-procedural screening for CAD with ICA is highly recommended, but only one third are therapeutics [4,5]. Due to age and comorbidities, heavy coronary calcifications may be common and challenge the diagnostic performance of coronary CT [15,16]. The aim of this study is to evaluate the feasibility, the image quality and the diagnostic performance of third generation DSCT with ultra-high pitch protocol for TAVI planning and coronary tree assessment and the impact of coronary calcifications on the diagnostic performance. In this study, we obtain an overall mean attenuation value > 400 HU in all vascular segments with very good reliability for prosthesis sizing (100 % procedural success rate). Considering ICA as the gold standard, we found that CT imaging for obstructive CAD ≥ 50 % had high sensitivity and NPV on a per-segment analysis, 97.6 % and 99.0 % respectively, and on a per-patient analysis, 97.8 % and 99.4 %, respectively. We also found that CT imaging for obstructive CAD ≥ 70 % had high sensitivity and NPV, on a per-segment analysis, 88.5 % and 96.8 % respectively and, on a per-patient analysis, 92.5 % and 98.1 %, respectively. These results suggest that obstructive CAD in TAVI 6
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Fig. 3. Coronary arteries evaluation in a 78-year-old female patient undergoing 192 × 2-DSCT for TAVI planning. Comparison between ICA (A) and CT curved planar reformation (B), axial (C), sagittal (D). The figure shows a diameter stenosis between 50–60 % and area obstruction between 80–90 % in LAD artery (white arrows), correctly evaluate with CT examination.
stratified the CT diagnostic performance using the same CCS threshold than in our study (low < 400, high ≥400), and they obtained a CT performance slightly lower than us concluding that in patients with CCS ≥ 400 CT performed less well. We hypothesize that these results should be mainly relate to the presence of beam hardening artifacts. In the most recent work, Annoni AD et al. [40], using a third generation 256-slices CT scanner, obtained sensitivity, specificity, PPV, NPV and diagnostic accuracy similar to us in the detection of coronary stenosis ≥50 % and ≥70 %, in the detection of ISR and in the CABGs stenosis. Unlike us, they used a retrospective ECG-gated acquisition to assess the heart and the thoracic aorta and a subsequent non–gated spiral scan to assess the abdominal aorta and iliac-femoral arteries and
Several previous studies [33–40] have looked to evaluate the diagnostic performance of coronary tree assessment in CT before TAVI planning and concluded that CT is a useful test to rule out significant obstructive CAD and to evaluate stents and CABGs patency. To the best of our knowledge, the present study is the work with the largest simple size and a prospective design with this aim and the only one that used a single prospective ECG-gated ultra-high pitch acquisition for aorta, iliac vessels and coronary artery assessments. Harris et al. [37] and Matsumoto et al. [38], obtained a mean CCS, respectively, similar than us, but they did not stratified the CT diagnostic performance based on CCS values. Rossi et al. [39] using a second generation DSCT with a retrospective ECG-gated protocol, 7
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Table 5 Diagnostic performance of pre-TAVI CT vs invasive coronary angiography in the assessment of intra stent re-stenosis and coronary artery bypass grafts stenosis. Se (%)
Sp (%)
PPV (%)
NPV (%)
DA (%)
92.6 (25/27) 83.3 (25/30)
70.6 (15/36) 70.6 (60/85)
62.5 (25/40) 50.0 (25/50)
94.7 (36/38) 92.3 (60/65)
78.2 (61/78) 73.9 (85/115)
95.0 (19/20) 93.3 (28/30)
94.1 (16/17) 85.7 (18/21)
95.0 (19/20) 90.3 (28/31)
94.1 (16/17) 90.0 (18/20)
94.6 (35/37) 90.2 (46/51)
Stents Number of patients
78
Patient-based
Number of stents
115
Vessel-based
Number of patients
37
Patient-based
Number of CABGs
51
Vessel-based
CABGs
Abbreviations. – Se: sensitivity; Sp: specificity; PPV: positive predictive value; NPV: negative predictive value; DA: diagnostic accuracy; CABG: coronary angiography by-pass graft. Table 6 Image quality according to Agatston coronary calcium scoring on segmentbased analysis. Threshold
Mean Agatston CCS
1
2
3
4
p value
< 400 (38.0 %) ≥400 (62.0 %)
141.2 ± 56.3 (47.2–234.9) 1099.2 ± 498.2 (625.1–2212.2)
3.2 %
18.5 %
16.1 %
62.2 %
p < 0.001
6.0 %
30.8 %
25.3 %
37.9 %
Table 8 Diagnostic performance of pre-TAVI CT vs invasive coronary angiography using a cut-off value ≥ 70 % of stenosis in two CCS groups. a
Segment-based Patient-based
Abbreviations. – CCS: coronary calcium scoring.
Segment-based
a
Segment-based Patient-based
Se (%)
Sp (%)
PPV (%)
NPV (%)
DA (%)
< 400 ≥400 < 400 ≥400
93.7 98.5 93.1 98.1
93.3 65.1 92.1 79.6
62.9 66.1 67.2 73.3
99.4 97.7 99.7 98.1
95.6 83.6 96.1 86.1
Patient-based
Segment-based Patient-based
Se (%)
Sp (%)
PPV (%)
NPV (%)
DA (%)
< 600 ≥600 < 600 ≥600
91.7 99.0 90.1 97.1
95.3 62.1 94.1 65.6
61.3 67.5 67.2 78.4
99.2 95.1 99.7 92.1
97.1 80.7 97.0 83.2
Sp (%)
PPV (%)
NPV (%)
DA (%)
≤400 > 400 ≤400 > 400
74.3 89.3 77.1 93.1
87.5 67.6 91.1 73.2
63.9 52.1 66.1 54.9
97.0 92.1 98.4 95.9
91.6 82.3 94.6 82.6
CCS
Se (%)
Sp (%)
PPV (%)
NPV (%)
DA (%)
≤600 > 600 ≤600 > 600
71.6 90.5 75.3 94.8
89.3 60.6 91.9 62.3
66.8 50.3 67.8 54.4
98.1 90.6 99.3 92.3
92.5 80.0 95.2 84.6
% % % %
% % % %
% % % %
% % % %
% % % %
% % % %
% % % %
% % % %
% % % %
% % % %
Abbreviations. – Se: sensitivity; Sp: specificity; PPV: positive predictive value; NPV: negative predictive value; DA: diagnostic accuracy.
of CAD in patients with aortic stenosis was 40–75 % [33–40], and the prevalence of CAD in our study was within the range. Second, images were acquired using a prospective ECG-gated protocol on a third generation DSCT scanner. However, the rapidly diffusion of CT scanner technology may soon overcome this limitation. In conclusion, our study revealed that using ultra-high pitch protocol with DSCT provides accurate information and very good image quality of both aorta and coronary tree with a high NPV for obstructive CAD. In patients with severe coronary calcifications, CT performed less well. Because CT is increasingly used for TAVI planning, these findings support the use of CT, helping to avoid unnecessary ICA. This would provide multiple health and cost benefits, thus reducing further radiation, amount of contrast dose, and hospitalization costs, as well as the potential risks related to invasive procedures.
b CCS
Se (%)
b
Table 7 Diagnostic performance of pre-TAVI CT vs invasive coronary angiography using a cut-off value ≥ 50 % of stenosis in two CCS groups.
CCS
CCS
Abbreviations. – CCS: coronary calcium scoring; Se: sensitivity; Sp: specificity; PPV: positive predictive value; NPV: negative predictive value; DA: diagnostic accuracy.
they did not considered the CCS. Finally, although radiation dose is not the topic of this work, with ultra-high pitch, mean ED is resulted 3.0 mSv. Radiation dose comparison between different CT protocols in TAVI planning could be a research field for further studies. Indeed, despite the radiation dose is not considered an issue because the high percentage are elderly patients, with the use of ultra-high pitch is possible to obtain, at any heart rate, an accurate coronary evaluation in TAVI planning, avoiding the use of a retrospective protocol, and following the “as low as reasonably achievable” radiation safety principle, based on the minimization of radiation doses and limiting the release of radioactive materials into the environment. Moreover, if the acquisition is not diagnostic, a following retrospective protocol for coronary assessment could be performed. There are some limitations in our study. First, PPV and NPV of CT coronary might be changed according to the prevalence of the study population. However, the previous study reported that the prevalence
Ethical standards All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/ or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study.
Disclosure The authors have no disclosure. 8
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Funding
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