34.03 Comparison of attenuation correction in myocardial SPECT using Gadolinium-153 line sources or low-dose CT

POSTER SESSION II SATURDAY, OCTOBER 1, 2005, 11:30 –1:30PM 34.01 AUTOMATED QUALITY CONTROL OF EMISSION-TRANSMISSION MISALIGNMENT FOR ATTENUATION CORRECTION IN MYOCARDIAL PERFUSION IMAGING WITH SPECT-CT SYSTEMS J Chen, SF Caputlu-Wilson, H Shi, JR Galt, TL Faber, EV Garcia Emory University School of Medicine, Atlanta, GA Background: Emission-transmission misalignment can be seen in myocardial perfusion imaging with SPECT-CT systems and impairs the accuracy of attenuation correction (AC). This study is to develop automated quality control (Auto-QC) to detect the critical misalignment that may impact AC. Methods: Auto-QC segmented the myocardium from emission reconstruction and the lung and mediastinum from attenuation map, respectively. A QC index (QCI) was calculated as the fraction of myocardial pixels either moving into the lung or moving out of the mediastinum. A NCAT (NURBS-based cardiac torso phantom) simulation study was used to determine a QCI threshold above that the misalignment would critically impact AC. The simulated attenuation map was shifted by 0.5, 1, 1.5, and 2 pixels (6.4 mm/pixel) along either x (left or right) or y (up or down) axes, and 0.5 and 1 pixels along both axes (up-left, up-right, down-left, down-right), respectively. Visual comparison of the AC images using the shifted attenuation maps with the AC images using the unshifted attenuation map by a blinded physician indicated the shifts that significantly distorted the AC images, and then the QCI threshold determined. Auto-QC was tested with 22 patient studies acquired by a GE Millennium VG/Hawkeye SPECT-CT system. Visual assessment of the emission and transmission images of these patients by a blinded physicist was used to check the Auto-QC accuracy. Results: The simulation showed that a one-pixel shift, no matter in which direction, resulted in artifacts in the AC images. Artifacts appeared at different locations for different directions. With the determined QCI threshold (3%), Auto-QC detected the critical misalignment concordantly with the visual QC (sensitivity: 1.00, specificity: 0.82). Conclusion: The QCI calculated by Auto-QC quantitatively indicated the significance of emission-transmission misalignment. Auto-QC with the QCI threshold yielded concordant results with the visual QC. The QCI threshold should next be confirmed with patient studies and the Auto-QC algorithm should next be prospectively validated with a large group of patient studies. 34.02 USE OF MULTIWIRE GAMMA CAMERA WITH NOVEL MOTION CORRECTION TO EXAMINE ADAPTATION TO TREADMILL EXERCISE V Cole, R Habtemarkos, L Sun, J Lacy, J Heo, AE Iskandrian University of Alabama at Birmingham Medical Center, Birmingham, AL Background: Previous radionuclide imaging studies examined cardiovascular adaptation to bicycle exercise with Tc-99m-labeled tracers and gated or 1st pass radionuclide angiography [RNA]. The treadmill studies were often limited by patient motion. However, treadmill is the preferred exercise modality due to greater sensitivity in the detection of coronary disease as well as the elicitation of greater hemodynamic stress. Furthermore, exercise LV function is an important prognostic predictor of cardiovascular events in high-risk patients. This study used 1st pass RNA to examine the changes in LV and RV EF and volumes and cardiac output [CO] with a short lived tracer [Ta-178] and a multiwire camera specially equipped with a 3D algorithm for motion correction. Methods: There were 25 men and 25 women with a mean age of 50 years who all had normal SPECT perfusion images. None had chest pain or ST changes during the symptom-limited treadmill exercise test. 1st pass RNA was obtained at rest and peak exercise. A novel motion correction algorithm used an electromagnetic position/orientation tracking system with a sensor output that consists of 6 degree-of-freedom (6-DOF) position information. S112

Results: The % mean and standard deviation of changes in HR, SBP, stroke volume [SV], CO, LV end diastolic volume [EDV], and LV end systolic volume [ESV] are listed in the table with the absolute increases and corresponding standard deviations of LVEF and RVEF. There were no significant differences between men and women. There were significant increases from rest to peak exercise in HR [P⬍0.01], SBP [P⬍0.01], LVEF [P⬍0.01], RVEF [P⬍0.01], SV [P⬍0.01], CO [P⬍0.01], EDV [P⬍0.01] and ESV [P⫽0.09 men, P⫽0.05 women]. Men Women

LVEF

RVEF

HR

SBP

SV

CO

EDV

ESV

12⫾9% 8⫾9%

10⫾8% 8⫾9%

69⫾20% 68⫾23%

30⫾14% 24⫾10%

98⫾63% 78⫾60%

226⫾90% 196⫾87%

65⫾52% 57⫾57%

23⫾56% 26⫾72%

The change in EDV was greater than the change in ESV in men and women accounting for the increase in EF [P⬍0.001 each]. Conclusions: The multiwire camera with its novel motion correction algorithm makes it possible to examine the pertinent physiological measurements during upright treadmill exercise that were not possible before due to patient motion. There are no gender-related differences in cardiovascular adaptation to exercise in this selected group of normal patients.

34.03 COMPARISON OF ATTENUATION CORRECTION IN MYOCARDIAL SPECT USING GADOLINIUM-153 LINE SOURCES OR LOW-DOSE CT A Kjaer, A Cortsen, M Federspiel, S Holm, M O’Connor, B Hesse Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet, University of Copenhagen, Denmark Background: The aim was on a head-to-head basis to compare attenuation correction (AC) in myocardial SPECT using either 153Gd transmission line sources or low-dose CT. Methods: SPECT was performed in 26 patients (mean age: 56 years, 14 men) using 99mTc-sestamibi and 1) a Millennium MG (GEMS) dual head camera with 153Gd transmission line sources for AC (interleaved), and 2) a Hawkeye (GEMS) with low-dose CT used for AC (sequential). In both systems scattered photons were acquired in a window below the 99mTc peak. All images were processed using the same iterative algorithm with scatter subtraction and AC. Images obtained with Gd attenuation maps and CT attenuation maps were compared with regard to impact on defects in 5 regions of the left ventricle (anterior, lateral, inferior, septal and apical) by consensus reading without knowledge of clinical or angiographic data. Results: A total of 26 studies were evaluated, of which 3 studies were omitted due to substantial difference in bowel activity between the investigations. Of the remaining 23 studies interpretations of noncorrected images were similar on both systems. In 17 of the patients patterns were identical following AC with Gd or low-dose CT: AC did not change interpretation in 9 cases and in 8 cases inferior defects were eliminated. In the remaining 6 studies, there were differences between the 2 AC systems: Using Gd-based AC 3 inferior defects disappeared which were not eliminated by low-dose CT AC. CAG in all 3 cases were normal. Furthermore, low-dose CT AC introduced 3 anterior defects whereas the Gd-based AC introduced no new defects in these cases. In one case CAG was normal, in one case two LAD stenoses (60 and 80%) were present. CAG was not available in the last discrepant case. Conclusions: Both Gd and CT AC have great impact on myocardial SPECT. However, when compared on a head-to-head basis in patients the two systems in some cases create important differences in the corrected images. Using CAG as reference, the Gd-based AC seems superior to the low-dose CT based AC system. Journal of Nuclear Cardiology July/August 2005