- Email: [email protected]
67: Adenosine Triphosphate Stress Myocardial Perfusion CT in Differential Diagnosis of Myocardial Ischemia and Infarction
S24
Journal of Cardiovascular Computed Tomography, Vol 2, No 4S, July/August 2008
64 Schmidt B, Raupach R, Flohr TG. Image-Based Method for the Calculation of Iodine Enhancement in the Myocardium from Dual Energy CT Images Siemens Healthcare Sector, Germany Introduction: Single energy CT images used for the assessment of first pass and late enhancement, e.g. for the diagnosis of myocardial ischemia, are typically limited by the fact that the measured CT values, e.g. from ROI measurements, in the myocardium represent only the sum of both, the enhancement due to iodine and the underlying tissue. The latter however might be inhomogeneous e.g. due to different tissue densities, fatty infiltrations or oedema. Hence, due to this masking effect measured CT values do not always correlate with the enhancement due to iodine. ECG-controlled Dual Energy CT imaging might allow the overcome this limitation by using DE post processing which provides information representing the pure iodine enhancement without underlying tissue structures. Methods: We used a dual source CT system (SOMATOM Definitio n, Siemens Healthcare Sector, Germany) to acquire simultaneously high and low kV data in ECG-controlled mode using the manufacturers recommended acquisition settings. Then data were reconstructed using dedicated dual energy reconstruction kernels and a so called three material decomposition into soft tissue, fat and iodine was performed. The resulting two new image stacks were showing images with pure iodine enhancement (a) and images with algorithm-based removed iodine enhancement (virtual non-contrast images) (b). To investigate our method we scanned phantoms and specimens containing hypo dense and fatty inserts, and areas with / without iodine to simulate a perfusion defects. Finally, the DE post-processed virtual non-contrast images were compared with real non-contrast images (c). Results: For both, phantoms and specimens, pure iodine enhancement images (a) and virtual non-contrast images (b) were calculated. The pure iodine images showed a significant enhancement only in those areas which contained iodine, whereas the virtual noncontrast images showed the hypo dense and fatty inserts without any iodine overlay. (b) and (c) were in good agreement. Conclusion: ECG-controlled Dual Energy CT data can be used for dual energy post processing. Our measurements show that using a dedicated three material decomposition, virtual non-contrast images and pure iodine images without underlying structures required for quantitative evaluations can be calculated from low and high kV images. 65 Kitagawa K, George RT, Chang HJ, Lima JAC, Lardo AC. Myocardial Perfusion Assessment Using Dynamic-mode 256-Row Multidetector Computed Tomography: Influence of Beam Hardening Correction Division of Cardiology, Department of Medicine, Johns Hopkins University, Baltimore, MD Introduction: We have previously shown that first-pass multidetectorrow computed tomography (MDCT) imaging of the heart allows assessment of myocardial perfusion. However, as a polychromatic Xray beam passes through an object, low energy photons are preferentially absorbed, and the X-ray beam increases its mean energy (beam hardening effect). The beam hardening artifacts caused by regions of high contrast concentration in the heart chambers and/or adjacent vessels may confound density measurements in the myocardium and thus prevent accurate perfusion assessment. The purpose of this study was to investigate the influence of beam hardening and the usefulness of beam hardening correction (BHC) software algorithms for myocardial perfusion assessment. Methods: Five dogs were prepared with either left anterior descending artery (LAD) stenosis (n=3) or left circumflex artery (LCX) stenosis (n=2) using an open chest model. Contrast enhanced dynamic 256x0.5mm MDCT was performed 5 minutes into adenosine infusion. MDCT images were reconstructed with and without BHC algorithm which mathematically corrects bean hardening by calculating the path length of X-ray in soft-tissue and high-attenuation material. Myocardial perfusion was measured semi-quantitatively using the myocardial upslope normalized by the left ventricular upslope (MUS/LVUS) based on the time-attenuation density curves generated from regions of interest placed in the anterior wall, septum and lateral wall on an axial
plane. MUS/LVUS was compared with microsphere-derived myocardial blood flow (MBF). Results: MUS/LVUS in the anterior wall was 0.070+/-0.047 without BHC vs. 0.095+/-0.049 with BHC (p<0.001) while in the lateral wall MUS/LVUS was 0.131+/-0.062 without BHC vs. 0.107+/-0.046 with BHC, (p<0.001). MUS/LVUP in the septum was unaffec ted by BHC (p=n.s.). Microsphere-derived MBF in the ROIs ranged from 0.5 to 5.3 ml/min/g. MUS/LVUP with BHC showed stronger correlation (r2=0.67) with microsphere-derived MBF compared to that without BHC (r2=0.41). The diagnostic performance of MUS/LVUS to detect regions with microsphere-derived MBF of <1.5ml/min/g represented by area under the receiver operating characteristics curve (Az) was 0.922 and 0.809, respectively, for with and without BHC (p=n.s.). Conclusion: Beam hardening artifacts confound MDCT assessment of myocardial perfusion. Application of BHC algorithm is helpful for improving accuracy ofmyocardial perfusion by MDCT. 66 Shikata F, Kido T, Kurata A, Higashino H, Inoue Y, Imagawa H, Kawachi K, Mochizuki T. Quantitative Assessment of Myocardial Blood Flow Using Adenosine Triphosphate Stress Multidetector-Row Computed Tomography Ehime University, Ehime, Japan Introduction: In this study, we sought to investigate the feasibility of using cardiac multidetector-row computed tomography (MDCT) technology in the quantitative assessment of the myocardial blood flow using adenosine triphosphate (ATP) load technique. Methods: The study group comprised 10 patients (7 men and 3 women, aged from 54 to 79 years, with a mean age of 64.2 years) who underwent cardiac cine MDCT using ATP-load techniqu e. Myocardial blood flow (MBF) was estimated from the slope of the linear regression equation with Patlak plots analysis. Results: The overall average MBF was 1.7709 ml/g/min. Mean MBF in territories with stenosis on coronary angiography (CAG) was 1.103 ml/g/min, while mean MBF in territories without stenosis was 2.057 ml/g/min (p<0.01). Average MBF in territories with moderate to severe ischemia on myocardial perfusion scintigraphy (MPS) was 1.264 ml/g/min, while mean MBF in territories without ischemia was 1.872ml/g/min (p<0.01) Conclusions: This study proposed the possibility of MDCT to quantify myocardial blood flow using first-pass dynamic data. 67 Kurata A, Kido T, Shikata F, Ishida N, Imagawa H , Abe M, Honda T, Sadamoto K, Okayama H, Higaki J, Inoue Y, Higashino H, Mochizuki T. Adenosine Triphosphate Stress Myocardial Perfusion CT in Differential Diagnosis of Myocardial Ischemia and Infarction Diagnostic and Therapeutic Radiology, Department of Organ Regeneration Surgery, Department of Integrated Medicine and Informatics, Ehime University Graduate School of Medicine, Japan Yotsuba Circulation Clinic, Japan Sadamoto Hospital, Japan Introduction: We had previously reported that qualitative and quantitative assessments of myocardial ischemia in patients with coronary artery disease (CAD) by adenosine triphosphate (ATP) stress multi-slice spiral computed tomography (MSCT). Based on the contrast dynamics, the myocardial perfusion specific CT scan protocol was tested for assessment of myocardial ischemia and infarction. Methods: Twelve patients with a high-probability of CAD (6 female; mean age, 66 years) gave informed consents and participate in the approved study. All 12 patients underwent ATP stre ss myocardial perfusion CT using 16-slice CT and 201-Thallium single photon emission computed tomography (SPECT), and coronary angiography (CAG), respectively. Ten patients underwent gadolin ium magnetic resonance imaging (MRI) as required. The ATP-stress myocardial perfusion CT had simple 4 steps; 1) intravenous ATP (0.16 mg/kg/min) infusion for 5 minutes, 2) the slow infusion of contrast medium at a rate of 2 ml/min for 100 ml (370 mg-iodine/ml) in 3 minutes later, 3) the stress image was acquired without bolus tracking after the contrastinjection, 4) the late image was acquired without additional contrast administration after 15 minutes from the stress image. Semiquantitative assessment of myocardial perfusion was performed with
3rd Annual Scientific Meeting 1.40 1.30
Transmural Perfusion Ratio
the CT-attenuation based color coded images (hot color as hyperenhanced; cold color as hypo-enhanced). Hypo-perfusion area (HPA) of perfusion CT and early defect (ED) of SPECT in each stress image, late iodine-enhancement (LIE) and gadolinium enhancement (LGE) in each late image were compared, respectively. Results: Twelve patients had 36 (12*3) coronary territories and 20 stenoses probed by CAG. Perfusion CT described 26 HPAs and SPECT described 18 EDs in the stress images. The agreement between perfusion CT and SPECT was 78 % (28/36, p<0.05). Eighteen matched territories of HPA(+)/ED(+) had 16 stenoses and 8 mismatched territories had 4 stenoses, respectively. Perfusion CT described 3 LIEs and MRI described 5 EDs in the late images. The agreement between perfusion CT and MRI was 92% (22/24, p<0.05). Conclusion: The ATP stress myocardial perfusion CT has simplic ity and potential for steady evaluation of myocardial ischemia and myocardial infarction (late enhancement) just like SPECT and MRI in patients with CAD.
S25
1.20 1.10 1.00 0.90 0.80
y = -0.0037x + 1.2325 R = 0.63, p<0.001
0.70 0.60 0.50 0.40 0
20
40
60
Percent Diameter Stenosis
68 George RT, Zadeh A, Kitagawa K, Chang HJ, Miller JM, Bluemke DA, Becker L, Texter J, Lardo AC, Lima JAC. Adenosine Stress 64 and 256 MDCT Perfusion Imaging: The Transmural Extent of Perfusion Abnormalities Predicts Atherosclerosis Causing Territorial Ischemia Johns Hopkins University, Baltimore, MD Introduction: The purpose of this study was to test the hypothesis that quantifying the transmural extent of subendocardial perfusion deficits using combined multidetector computed tomography (MDCT) angiography and adenosine stress MDCT myocardial perfusion imaging (MPI) can accurately diagnose atherosclerosis causing regional ischemia on SPECT MPI in the presence of atherosclerosis. Methods: Forty-three consecutive patients with suspected coronary artery disease and a history of abnormal SPECT MPI underwent adenosine (140 mcg/kg/min) stress MDCT perfusion imaging using 64row (N=24) and 256-row (N=19) MDCT. Twenty-six pat ients went on to have invasive coronary angiography performed. Using a 16segment model, the myocardium was divided into sectors and each sector was sub-divided into subendocardial, mid-myocardial, and subepicardial layers. The mean Hounsfield units (HU) of each sector were measured throughout the layers of myocardium and a transmural perfusion ratio (TPR) was calculated (Subendocardial HU / Subepicardial HU). The threshold for an abnormal TPR was defined by one standard deviation below the mean TPR in a subset of patients with normal coronary arteries defined by invasive coronary angiography (ICA). MDCT MPI results were combined with MDCT angiography results and compared with the combination of MDCT angiography and SPECT MPI (gold standard). Results: The mean TPR in fourteen patients with normal coronary arteries confirmed by ICA among 224 myocardial sectors was 1.12±0.13. Based on these results, an abnormal TPR was defined as <0.99. Interobserver variability for the measurement of TPR was good with =0.72 and =0.63, on rest and stress images, respectively. There was a statistically significant correlation between the TPR and percent diameter stenosis determined by quantitative coronary angiography (R=0.63, p<0.001, see Figure). On a per-vessel/territory basis, the sensitivity, specificity, positive and n egative predictive value for the combination of MDCT angiography and MDCT perfusion imaging to predict regional ischemia on SPECT MPI in the presence of atherosclerosis was 85.7%, 94.9%, 90.0%, and 92.5%, respectively. When restricting the analysis to the 256-row MDCT group, where rest and stress perfusion imaging was available, MDCT MPI identified reversible ischemia on SPECT in 11 of 13 patients. Conclusions: MDCT MPI, when combined with MDCT angiography, can accurately identify atherosclerosis causing regional perfusion deficits on SPECT MPI. The TPR correlates well with percent diameter stenosis and rest and stress MDCT MPI can accurately identify reversible ischemia.
80
100
Journal of Cardiovascular Computed Tomography, Vol 2, No 4S, July/August 2008
64 Schmidt B, Raupach R, Flohr TG. Image-Based Method for the Calculation of Iodine Enhancement in the Myocardium from Dual Energy CT Images Siemens Healthcare Sector, Germany Introduction: Single energy CT images used for the assessment of first pass and late enhancement, e.g. for the diagnosis of myocardial ischemia, are typically limited by the fact that the measured CT values, e.g. from ROI measurements, in the myocardium represent only the sum of both, the enhancement due to iodine and the underlying tissue. The latter however might be inhomogeneous e.g. due to different tissue densities, fatty infiltrations or oedema. Hence, due to this masking effect measured CT values do not always correlate with the enhancement due to iodine. ECG-controlled Dual Energy CT imaging might allow the overcome this limitation by using DE post processing which provides information representing the pure iodine enhancement without underlying tissue structures. Methods: We used a dual source CT system (SOMATOM Definitio n, Siemens Healthcare Sector, Germany) to acquire simultaneously high and low kV data in ECG-controlled mode using the manufacturers recommended acquisition settings. Then data were reconstructed using dedicated dual energy reconstruction kernels and a so called three material decomposition into soft tissue, fat and iodine was performed. The resulting two new image stacks were showing images with pure iodine enhancement (a) and images with algorithm-based removed iodine enhancement (virtual non-contrast images) (b). To investigate our method we scanned phantoms and specimens containing hypo dense and fatty inserts, and areas with / without iodine to simulate a perfusion defects. Finally, the DE post-processed virtual non-contrast images were compared with real non-contrast images (c). Results: For both, phantoms and specimens, pure iodine enhancement images (a) and virtual non-contrast images (b) were calculated. The pure iodine images showed a significant enhancement only in those areas which contained iodine, whereas the virtual noncontrast images showed the hypo dense and fatty inserts without any iodine overlay. (b) and (c) were in good agreement. Conclusion: ECG-controlled Dual Energy CT data can be used for dual energy post processing. Our measurements show that using a dedicated three material decomposition, virtual non-contrast images and pure iodine images without underlying structures required for quantitative evaluations can be calculated from low and high kV images. 65 Kitagawa K, George RT, Chang HJ, Lima JAC, Lardo AC. Myocardial Perfusion Assessment Using Dynamic-mode 256-Row Multidetector Computed Tomography: Influence of Beam Hardening Correction Division of Cardiology, Department of Medicine, Johns Hopkins University, Baltimore, MD Introduction: We have previously shown that first-pass multidetectorrow computed tomography (MDCT) imaging of the heart allows assessment of myocardial perfusion. However, as a polychromatic Xray beam passes through an object, low energy photons are preferentially absorbed, and the X-ray beam increases its mean energy (beam hardening effect). The beam hardening artifacts caused by regions of high contrast concentration in the heart chambers and/or adjacent vessels may confound density measurements in the myocardium and thus prevent accurate perfusion assessment. The purpose of this study was to investigate the influence of beam hardening and the usefulness of beam hardening correction (BHC) software algorithms for myocardial perfusion assessment. Methods: Five dogs were prepared with either left anterior descending artery (LAD) stenosis (n=3) or left circumflex artery (LCX) stenosis (n=2) using an open chest model. Contrast enhanced dynamic 256x0.5mm MDCT was performed 5 minutes into adenosine infusion. MDCT images were reconstructed with and without BHC algorithm which mathematically corrects bean hardening by calculating the path length of X-ray in soft-tissue and high-attenuation material. Myocardial perfusion was measured semi-quantitatively using the myocardial upslope normalized by the left ventricular upslope (MUS/LVUS) based on the time-attenuation density curves generated from regions of interest placed in the anterior wall, septum and lateral wall on an axial
plane. MUS/LVUS was compared with microsphere-derived myocardial blood flow (MBF). Results: MUS/LVUS in the anterior wall was 0.070+/-0.047 without BHC vs. 0.095+/-0.049 with BHC (p<0.001) while in the lateral wall MUS/LVUS was 0.131+/-0.062 without BHC vs. 0.107+/-0.046 with BHC, (p<0.001). MUS/LVUP in the septum was unaffec ted by BHC (p=n.s.). Microsphere-derived MBF in the ROIs ranged from 0.5 to 5.3 ml/min/g. MUS/LVUP with BHC showed stronger correlation (r2=0.67) with microsphere-derived MBF compared to that without BHC (r2=0.41). The diagnostic performance of MUS/LVUS to detect regions with microsphere-derived MBF of <1.5ml/min/g represented by area under the receiver operating characteristics curve (Az) was 0.922 and 0.809, respectively, for with and without BHC (p=n.s.). Conclusion: Beam hardening artifacts confound MDCT assessment of myocardial perfusion. Application of BHC algorithm is helpful for improving accuracy ofmyocardial perfusion by MDCT. 66 Shikata F, Kido T, Kurata A, Higashino H, Inoue Y, Imagawa H, Kawachi K, Mochizuki T. Quantitative Assessment of Myocardial Blood Flow Using Adenosine Triphosphate Stress Multidetector-Row Computed Tomography Ehime University, Ehime, Japan Introduction: In this study, we sought to investigate the feasibility of using cardiac multidetector-row computed tomography (MDCT) technology in the quantitative assessment of the myocardial blood flow using adenosine triphosphate (ATP) load technique. Methods: The study group comprised 10 patients (7 men and 3 women, aged from 54 to 79 years, with a mean age of 64.2 years) who underwent cardiac cine MDCT using ATP-load techniqu e. Myocardial blood flow (MBF) was estimated from the slope of the linear regression equation with Patlak plots analysis. Results: The overall average MBF was 1.7709 ml/g/min. Mean MBF in territories with stenosis on coronary angiography (CAG) was 1.103 ml/g/min, while mean MBF in territories without stenosis was 2.057 ml/g/min (p<0.01). Average MBF in territories with moderate to severe ischemia on myocardial perfusion scintigraphy (MPS) was 1.264 ml/g/min, while mean MBF in territories without ischemia was 1.872ml/g/min (p<0.01) Conclusions: This study proposed the possibility of MDCT to quantify myocardial blood flow using first-pass dynamic data. 67 Kurata A, Kido T, Shikata F, Ishida N, Imagawa H , Abe M, Honda T, Sadamoto K, Okayama H, Higaki J, Inoue Y, Higashino H, Mochizuki T. Adenosine Triphosphate Stress Myocardial Perfusion CT in Differential Diagnosis of Myocardial Ischemia and Infarction Diagnostic and Therapeutic Radiology, Department of Organ Regeneration Surgery, Department of Integrated Medicine and Informatics, Ehime University Graduate School of Medicine, Japan Yotsuba Circulation Clinic, Japan Sadamoto Hospital, Japan Introduction: We had previously reported that qualitative and quantitative assessments of myocardial ischemia in patients with coronary artery disease (CAD) by adenosine triphosphate (ATP) stress multi-slice spiral computed tomography (MSCT). Based on the contrast dynamics, the myocardial perfusion specific CT scan protocol was tested for assessment of myocardial ischemia and infarction. Methods: Twelve patients with a high-probability of CAD (6 female; mean age, 66 years) gave informed consents and participate in the approved study. All 12 patients underwent ATP stre ss myocardial perfusion CT using 16-slice CT and 201-Thallium single photon emission computed tomography (SPECT), and coronary angiography (CAG), respectively. Ten patients underwent gadolin ium magnetic resonance imaging (MRI) as required. The ATP-stress myocardial perfusion CT had simple 4 steps; 1) intravenous ATP (0.16 mg/kg/min) infusion for 5 minutes, 2) the slow infusion of contrast medium at a rate of 2 ml/min for 100 ml (370 mg-iodine/ml) in 3 minutes later, 3) the stress image was acquired without bolus tracking after the contrastinjection, 4) the late image was acquired without additional contrast administration after 15 minutes from the stress image. Semiquantitative assessment of myocardial perfusion was performed with
3rd Annual Scientific Meeting 1.40 1.30
Transmural Perfusion Ratio
the CT-attenuation based color coded images (hot color as hyperenhanced; cold color as hypo-enhanced). Hypo-perfusion area (HPA) of perfusion CT and early defect (ED) of SPECT in each stress image, late iodine-enhancement (LIE) and gadolinium enhancement (LGE) in each late image were compared, respectively. Results: Twelve patients had 36 (12*3) coronary territories and 20 stenoses probed by CAG. Perfusion CT described 26 HPAs and SPECT described 18 EDs in the stress images. The agreement between perfusion CT and SPECT was 78 % (28/36, p<0.05). Eighteen matched territories of HPA(+)/ED(+) had 16 stenoses and 8 mismatched territories had 4 stenoses, respectively. Perfusion CT described 3 LIEs and MRI described 5 EDs in the late images. The agreement between perfusion CT and MRI was 92% (22/24, p<0.05). Conclusion: The ATP stress myocardial perfusion CT has simplic ity and potential for steady evaluation of myocardial ischemia and myocardial infarction (late enhancement) just like SPECT and MRI in patients with CAD.
S25
1.20 1.10 1.00 0.90 0.80
y = -0.0037x + 1.2325 R = 0.63, p<0.001
0.70 0.60 0.50 0.40 0
20
40
60
Percent Diameter Stenosis
68 George RT, Zadeh A, Kitagawa K, Chang HJ, Miller JM, Bluemke DA, Becker L, Texter J, Lardo AC, Lima JAC. Adenosine Stress 64 and 256 MDCT Perfusion Imaging: The Transmural Extent of Perfusion Abnormalities Predicts Atherosclerosis Causing Territorial Ischemia Johns Hopkins University, Baltimore, MD Introduction: The purpose of this study was to test the hypothesis that quantifying the transmural extent of subendocardial perfusion deficits using combined multidetector computed tomography (MDCT) angiography and adenosine stress MDCT myocardial perfusion imaging (MPI) can accurately diagnose atherosclerosis causing regional ischemia on SPECT MPI in the presence of atherosclerosis. Methods: Forty-three consecutive patients with suspected coronary artery disease and a history of abnormal SPECT MPI underwent adenosine (140 mcg/kg/min) stress MDCT perfusion imaging using 64row (N=24) and 256-row (N=19) MDCT. Twenty-six pat ients went on to have invasive coronary angiography performed. Using a 16segment model, the myocardium was divided into sectors and each sector was sub-divided into subendocardial, mid-myocardial, and subepicardial layers. The mean Hounsfield units (HU) of each sector were measured throughout the layers of myocardium and a transmural perfusion ratio (TPR) was calculated (Subendocardial HU / Subepicardial HU). The threshold for an abnormal TPR was defined by one standard deviation below the mean TPR in a subset of patients with normal coronary arteries defined by invasive coronary angiography (ICA). MDCT MPI results were combined with MDCT angiography results and compared with the combination of MDCT angiography and SPECT MPI (gold standard). Results: The mean TPR in fourteen patients with normal coronary arteries confirmed by ICA among 224 myocardial sectors was 1.12±0.13. Based on these results, an abnormal TPR was defined as <0.99. Interobserver variability for the measurement of TPR was good with =0.72 and =0.63, on rest and stress images, respectively. There was a statistically significant correlation between the TPR and percent diameter stenosis determined by quantitative coronary angiography (R=0.63, p<0.001, see Figure). On a per-vessel/territory basis, the sensitivity, specificity, positive and n egative predictive value for the combination of MDCT angiography and MDCT perfusion imaging to predict regional ischemia on SPECT MPI in the presence of atherosclerosis was 85.7%, 94.9%, 90.0%, and 92.5%, respectively. When restricting the analysis to the 256-row MDCT group, where rest and stress perfusion imaging was available, MDCT MPI identified reversible ischemia on SPECT in 11 of 13 patients. Conclusions: MDCT MPI, when combined with MDCT angiography, can accurately identify atherosclerosis causing regional perfusion deficits on SPECT MPI. The TPR correlates well with percent diameter stenosis and rest and stress MDCT MPI can accurately identify reversible ischemia.
80
100