A Comparison of Heart Rate Response between 12 hours Caffeine Abstinence and 24 hours in Adenosine Stress Myocardial Perfusion Imaging.

The aim of this study was to examine whether the heart rate response to adenosine differs after 12 hours [Good control (Good-C)] versus 24 hours [Excellent control (Exc-C)] of caffeine abstinence in adenosine stress thallium-201 (TL) myocardial perfusion imaging (MPI). Patients (n=729) with suspected ischemic heart disease underwent adenosine TL-MPI after 12 (n=226) and 24 (n=503) hours of caffeine abstinence. There was not significant differences between the heart rate of Exc-C and Good-C in 0-2 min after adenosine infusion (0 min 63.7±9.5 versus 63.7±10.0, 1 min 66.4±10.6 versus 65.3±10.5, 2 min 72.3±11.2 versus 70.6±11.4). The heart rate of Exc-C was higher compared to Good-C in 3-6 min after adenosine infusion (3 min 75.6 ±11.7 versus 73.3±11.6 p=0.013, 4 min 79.2±12.9 versus 76.7±12.2 p=0.012, 5 min 79.4±12.6 versus 76.8±12.4 p=0.009, 6 min 79.4±12.5 versus 77.0±12.3 p=0.016). Therefore, the longer caffeine abstinence, namely 24 hours self-restraint, is effective in adenosine TL-MPI.

Quantification of the myocardial area at risk using coronary CT angiography and Voronoi algorithm-based myocardial segmentation.

OBJECTIVES: The purpose of this study was to estimate the myocardial area at risk (MAAR) using coronary computed tomography angiography (CTA) and Voronoi algorithm-based myocardial segmentation in comparison with single-photon emission computed tomography (SPECT). METHODS: Thirty-four patients with coronary artery disease underwent 128-slice coronary CTA, stress/rest thallium-201 SPECT, and coronary angiography (CAG). CTA-based MAAR was defined as the sum of all CAG stenosis (>50%) related territories (the ratio of the left ventricular volume). Using automated quantification software (17-segment model, 5-point scale), SPECT-based MAAR was defined as the number of segments with a score above zero as compared to the total 17 segments by summed stress score (SSS), difference (SDS) score map, and comprehensive SPECT interpretation with either SSS or SDS best correlating CAG findings (SSS/SDS). Results were compared using Pearson's correlation coefficient. RESULTS: Forty-nine stenoses were observed in 102 major coronary territories. Mean value of CTA-based MAAR was 28.3 ± 14.0%. SSS-based, SDS-based, and SSS/SDS-based MAAR was 30.1 ± 6.1%, 20.1 ± 15.8%, and 26.8 ± 15.7%, respectively. CTA-based MAAR was significantly related to SPECT-based MAAR (r = 0.531 for SSS; r = 0.494 for SDS; r = 0.814 for SSS/SDS; P < 0.05 in each). CONCLUSIONS: CTA-based Voronoi algorithm myocardial segmentation reliably quantifies SPECT-based MAAR. KEY POINTS: • Voronoi algorithm allows for three-dimensional myocardial segmentation of coronary CT angiography • Stenosis-related CT myocardial territories correlate to SPECT based area at risk • CT angiography myocardial segmentation may assist in clinical decision-making.

[Intravenous adenosine and radiopharmaceutical injection in the same line was feasible in adenosine stress myocardial perfusion. imaging].

Adenosine stress myocardial perfusion imaging was performed with an intravenous adenosine and radiopharmaceutical injection in the same line. A syringe containing 720 µg/kg of adenosine in 40 ml of saline was prepared and injected at the constant infusion rate of 400 ml/h. Adenosine was temporarily stopped by the stopcock when 1.5 ml of thallium was injected for 0.5 second from the three-way stopcock with two ways opened. Thereafter, the stopcock was returned to the original position in 0.5 second, and adenosine flow returned to the constant flow rate again. In this method, 0.75% of adenosine total dose was injected at a rate of 3.0 ml/s and adenosine was stopped for 3.6 second. There were no significant differences in either effects and adverse events of adenosine between this method and two intravenous injection line method. Adenosine stress in one venous line method would be an easy method maintaining the dose effect and safety.

Feasibility of Simple Evaluation of Coronary Artery Calcium Using a Number of Chest Computed Tomography Slices: A Multicenter Study.

Objective: We aimed to evaluate the visual measurements of coronary artery calcium (CAC) on nonelectrocardiogram (ECG)-gated chest computed tomography (CT) using a simple scoring method that involves counting the number of CT slices containing CAC. Materials and Methods: We analyzed 163 participants who underwent both coronary and chest CT examinations at six centers within 3 months. Agatston scores were calculated on standard ECG-gated scans and classified as none (0), mild (1-99), moderate (100-400), or severe (>400). Next, chest CT images were reconstructed to standard 5.0 mm axial slices. Then, CAC on chest CT scans was measured using two methods: the Weston score (sum of the assigned score of each vessel, range: 0-12) and number of slices showing CAC (Ca-slice#). Results: When the Weston score and Ca-slice# were divided into four levels according to the optimal divisional levels corresponding to the Agatston score classes, good agreements with the 4-grade Agatston score were observed (kappa value=0.610 and 0.794, respectively). The sensitivity and specificity of Ca-slice# ≥9 to identify severe Agatston scores of >400 were 86% and 96%, respectively. Conclusion: The Ca-slice#, a simple scoring method using chest CT scans, was in good agreement with the ECG-gated Agatston score.

Transmural perfusion gradient in adenosine triphosphate stress myocardial perfusion computed tomography.

BACKGROUND: The aim of the present study was to assess semi-quantification of myocardial perfusion using adenosine triphosphate (ATP)-stress myocardial perfusion computed tomography (MPCT) in patients with coronary artery disease (CAD). METHODS AND RESULTS: Seventeen patients with CAD underwent ATP-stress MPCT, stress myocardial perfusion scintigraphy (MPS) and coronary angiography (CAG). With ATP loading (0.16 mg·kg⁻¹·min⁻¹, 5 min) and slow infusion of contrast medium (2 ml/s, 100 ml), stress images were acquired using prospective electrocardiogram-gated 64-slice CT. Stress MPCT images were analyzed according to the transmural perfusion gradient (TMPG; difference between subendocardial and epicardial attenuation, divided by wall thickness; Hounsfield units [HU]/mm) per segment, and summed TMPG was compared with those of stress MPS and CAG per territory and patient, respectively. There were 36 CAG-proved stenotic vessels in 51 (17 × 3) territories. There were significant correlations between TMPG and MPS stress score per segment, per territory and per patient, respectively (P<0.05). Summed TMPG in territories with and without >70% coronary stenosis was 32.3HU/mm (-1.9~90.9) and 14.5 HU/mm (-5.6~38.4; P<0.05). For detecting coronary artery stenosis, sensitivity, specificity, positive and negative predictive values using the summed TMPG were 72%, 87%, 93% and 57%, in comparison with summed MPS (64%, 73%, 85%, and 46%). CONCLUSIONS: Semi-quantification of myocardial perfusion using TMPG has great potential to evaluate the severity of myocardial ischemia, similarly to MPS score.

Regional myocardial blood flow measured by stress multidetector computed tomography as a predictor of recovery of left ventricular function after coronary artery bypass grafting.

BACKGROUND: Multidetector-row computed tomography (MDCT) applications have expanded to evaluation of myocardial blood flow (MBF) and viability. We quantified regional MBF pre- and post-coronary artery bypass grafting (CABG) using adenosine stress and cardiac 64-MDCT, and investigated whether the results predict MBF and left ventricular (LV) function recovery after CABG. METHODS: We studied 321 regions in 19 CABG patients who underwent adenosine stress 64-row MDCT perfusion imaging and cine magnetic resonance imaging pre- and post-CABG. Myocardial blood flow was estimated from linear regression equation slopes using Patlak plot analyses and compared with LV function by measuring wall thickening (%WT) using cine magnetic resonance imaging. RESULTS: Overall mean MBFs were 1.39 +/- 0.49 and 1.95 +/- 0.49 mL/(g min) pre- and post-CABG (P < .0001). Myocardial blood flow in revascularized areas increased significantly (pre-CABG 1.18 +/- 0.45, post-CABG 1.99 +/- 0.66 mL/[g min], P < .001), whereas nonischemic areas showed no difference (1.79 +/- 0.70 and 1.97 +/- 0.46 mL/[g min], P = .14). Revascularized areas with preoperative MBF > or = 0.9 mL/(g min) showed significantly greater MBF improvement than those with preoperative MBF <0.9 mL/(g min) (P = .04). In patients with preoperative LV dysfunction (ejection fraction <40%), %WT in revascularized areas with pre-CABG MBF > or = 0.9 mL/(g min) improved significantly after CABG (pre-%WT 40.9 +/- 22.9, post-%WT 52.8 +/- 20.6, P = .03) versus those with pre-CABG MBF <0.9 mL/(g min) (pre-%WT 53.2 +/- 35.5, post-%WT 42.5 +/- 17.0, P = .40). CONCLUSIONS: Our results demonstrated more significantly increased MBF post-CABG than pre-CABG, particularly in revascularized areas. Regional MBF before CABG may predict MBF and LV function recovery, in the short term, after CABG.

Peri-infarct dysfunction in post-myocardial infarction: assessment of 3-T tagged and late enhancement MRI.

OBJECTIVE: To determine LV function at different distances from myocardial infarction (MI) by using 3-T tagged MRI and late gadolinium enhancement (LGE). METHODS: Cardiac MR images were acquired from 21 patients with previous MI. The harmonic phase (HARP) method was used to calculate radial and circumferential strain (RS, CS). The two strains were synchronised by subtracting the CS from the RS at the same time, and this was defined as the efficient strain (ES). Peak strain (P-RS, P-CS, P-ES) and time to peak strain (T-RS, T-CS, T-ES) were used as estimates of contractile function. Based on the presence of LGE, myocardium was classified into infarct, border zone, adjacent and remote areas. RESULTS: P-RS and P-ES were significantly greater for remote than for adjacent and infarct areas. P-CS values were significantly greater for remote and border zone than for infarct areas. T-RS and T-ES were significantly shorter for remote and border zone than for infarct areas. T-CS was significantly shorter for border zone than for infarct areas. CONCLUSION: Contractile dysfunction demonstrated by peak strain was correlated with location at different distances from the infarct. In the border zone, contractile deformation was characterised as earlier T-RS, T-CS and T-ES and greater P-CS than in the infarct area.

Myocardial ischemia in acute coronary syndrome: assessment using 64-MDCT.

OBJECTIVE: We investigated the performance of 64-MDCT myocardial imaging in assessing myocardial ischemia in acute coronary syndrome (ACS). MATERIALS AND METHODS: Cardiac CT was performed in 35 patients with ACS: 24 patients with acute myocardial infarction (AMI) and 11 patients with unstable angina pectoris (UAP). We reconstructed 2D myocardial images at diastolic and systolic phases using the same raw data as those used for coronary CT angiography. The CT number in the myocardium was used as an estimate of ischemia. The myocardium was shown using a color scale that depicts faint low-density areas more clearly than gray scale. We evaluated the variations in myocardial enhancement during the cardiac cycle in the territory of the culprit lesion. In addition, we classified patients on the basis of the transmurality of myocardial enhancement and examined whether this feature correlates with myocardial damage. RESULTS: Myocardial imaging at systole showed myocardial hypoenhancement in territories of the culprit lesion in 91% of patients with ACS, 96% of patients with AMI, and 75% of patients with UAP. The hypoenhancement areas at systole tended to be more extensive than those at diastole. The transmural extent of hypoenhancement at systole correlated with myocardial damage, which was shown by myocardial biomarkers. CONCLUSION: CT myocardial imaging can be used to assess myocardial ischemia in the appropriate region of ACS with high sensitivity.

Quantification of myocardial perfusion by contrast-enhanced 64-MDCT: characterization of ischemic myocardium.

OBJECTIVE: Assessment of hemodynamic changes in ischemic cardiac segments at rest using CT has yet to be performed. We hypothesized that variations in subendocardial perfusion during the cardiac cycle might be related to the appearances of ischemia. The purpose of this study was to investigate myocardial perfusion in ischemic segments using contrast-enhanced 64-MDCT. SUBJECTS AND METHODS: We performed cardiac MDCT at rest and stress/rest (201)Tl myocardial perfusion scintigraphy (MPS) in 34 patients with suspected coronary artery disease. We reconstructed 2D long- and short-axis cardiac images in diastolic and systolic phases using raw data from coronary CT angiography. The attenuation value (in Hounsfield units) in the myocardium was used as an estimate of myocardial perfusion. We measured the subendocardial intensity of 17 segments according to the American Heart Association classification. Systolic perfusion or diastolic perfusion was calculated by dividing the subendocardial intensity at systole or diastole, respectively, for each segment by the mean value across all segments for each patient. We used stress/rest MPS to evaluate the variation in myocardial perfusion at systole and diastole for the segments diagnosed as ischemic or nonischemic. RESULTS: Systolic perfusion for ischemic segments was significantly lower than that for nonischemic segments in 15 of 17 segments. The difference between systolic perfusion and diastolic perfusion in ischemic segments was significantly lower than that in nonischemic segments (14 of 17 segments). There was no significant difference in diastolic perfusion between ischemic and nonischemic segments (15 of 17 segments). CONCLUSION: Our results suggest that a pattern of subendocardial hypoperfusion at systole and normal perfusion at diastole characterizes ischemic myocardium.

Analysis of microvascularity after reperfused acute myocardial infarction using the maximum slope method of contrast-enhanced magnetic resonance imaging.

PURPOSE: The aim of this study was to analyze microvas-cularity after reperfused acute myocardial infarction (AMI) using the maximum slope method of contrastenhanced cardiac magnetic resonance imaging (CMR). MATERIALS AND METHODS: CMR and resting (201)T1 single photon emission computed tomography (SPECT) images were obtained in 30 consecutive patients after reperfused AMI and 10 controls. After bolus injection of gadolinium diethylenetriamine pentaacetic acid, first-pass CMR images were obtained using the True-FISP sequence. Time-intensity curves were generated by measuring the signal intensity in the myocardium and left ventricle. The arterial input function was obtained from the left ventricular time-intensity curve. On the basis of the maximum slope method, the microvascular index (MVI) was calculated by dividing the maximum initial upslope of the myocardium by the initial upslope of the left ventricle. RESULTS: The MVI was significantly lower in the segments related to the occluded coronary artery. MVIs in segments with (201)Tl uptake of 50%-59% of peak were significantly lower than in those with (201)Tl uptake of 60%-69%. MVIs in segments with (201)Tl uptake of <50% of peak were significantly lower than in those with (201)Tl uptake of 50%-59%. CONCLUSION: This study presents a method that directly assesses microvascularity after reperfused AMI.

Intravenous IgG Reduces Pathogenic Autoantibodies, Serum IL-6 Levels, and Disease Severity in Experimental Bullous Pemphigoid Models.

Bullous pemphigoid (BP) is an autoimmune blistering disease characterized by autoantibodies to COL17. Currently, systemic corticosteroids are used as first-line treatments for BP; alternatively, intravenous administration of high-dose IgG (IVIG) has been shown to be effective for patients with steroid-resistant BP in clinical practice. However, the effect of IVIG on BP has not fully been investigated. To examine the effects and mechanisms of action of IVIG against BP, we performed IVIG experiments using two experimental BP mouse models. One is a passive-transfer BP model that reproduces subepidermal separation in neonatal mice by the passive transfer of IgGs against COL17, such as polyclonal or monoclonal mouse IgG or IgG from BP patients. The other is an active BP model that continuously develops a disease phenotype in adult mice. IVIG decreased pathogenic IgG and the disease scores in both models. Injected IVIG distributed throughout the dermis and the intercellular space of the lower epidermis. Notably, IVIG inhibited the increase of IL-6 in both models, possibly by suppressing the production of IL-6 by keratinocytes. These results suggest that the inhibitory effects of IVIG on BP are associated with the reduction of pathogenic IgG and the modulation of cytokine production.

Evaluation of acute myocardial infarction with late enhancement pattern on MRI compared with 201Tl and 99mTc-hydroxymethylenediphosphonate (HMDP) dual single photon emission computed tomography (SPECT) images.

UNLABELLED: The purpose of this study is to evaluate reperfused acute myocardial infarction with late enhancement (LE) pattern on contrast-enhanced magnetic resonance imaging compared with myocardial single photon emission computed tomography (SPECT) images. MATERIALS AND METHODS: Magnetic resonance and 201Tl and 99mTc-hydroxymethylenediphosphonate SPECT images were obtained from 40 patients within 6 days of reperfused myocardial infarction. We assessed the myocardial LE pattern using the true fast imaging with steady-state free precession sequence after the injection of Gd-DTPA. Patients were classified into 3 groups: group 1 included patients with localized endocardial enhancement; group 2, patients with transmural enhancement; and group 3, patients with LE and a residual defect. RESULTS: There were 9 patients (23%) in group 1, 15 (38%) in group 2, and 15 (38%) in group 3. In 1 patient, LE was not detected (3%). The %201Tl uptake for the infarcted area was 60.7 +/- 7.2 (mean +/- SD) for group 1, 49.5 +/- 12.3 (P < 0.05 vs. group 1) for group 2, and 36.9 +/- 8.2 (P < 0.0001 vs. group 1, P = 0.005 vs. group 2) for group 3. An overlap pattern of 201Tl and 99mTc was observed in 9 of the group 1 patients (100%) and 9 of the group 2 patients (60%), but was not evident in group 3 (0%). CONCLUSIONS: LE with residual defect is an important indicator of microvascular obstruction after reperfusion therapy.

Quantitative assessment of regional left ventricular wall thickness and thickening using 16 multidetector-row computed tomography: comparison with cine magnetic resonance imaging.

PURPOSE: The purpose of this study was to investigate the feasibility of retrospective electrocardiography-gated multidetector-row computed tomography (MDCT) in the assessment left ventricular (LV) wall thickness and thickening and to test its validity compared to cine magnetic resonance imaging (MRI) as a standard of reference. MATERIALS AND METHODS: We enrolled 19 patients who underwent both cardiac MDCT and cine MRI. End-diastolic wall thickness (EDWT) and end-systolic wall thickness (ESWT) were measured in 16 myocardial segments. Percent systolic wall thickening (%SWT) was generated from the EDWT and ESWT. Nondiagnostic myocardial segments were excluded. Correlation and agreement between MDCT and cine MRI were analyzed. RESULTS: Segmental assessability values were 86.2% (262/304) and 92.1% (280/304) for MDCT and cine MRI, respectively. In assessable segments by both modalities (80.9%, 246/304), a significant correlation between MDCT and MRI was found (r = 0.89, 0.85, and 0.61, for EDWT, ESWT, and %SWT, respectively; all P < 0.05). Mean EDWT and ESWT values by MDCT were slightly lower than those by cine MRI (9.8 +/- 3.6 vs. 10.0 +/- 3.7 mm and 13.8 +/- 4.4 vs. 14.1 +/- 4.3 mm, respectively; both P < 0.01). Bland-Altman analysis revealed acceptable limits of agreement between MDCT and Cine MRI. CONCLUSION: MDCT is a feasible method to assess regional LV wall thickness and systolic thickening.

Cardiac imaging using 256-detector row four-dimensional CT: preliminary clinical report.

PURPOSE: Along with the increase of detector rows on the z-axis and a faster gantry rotation speed, the spatial and temporal resolutions of the multislice computed tomography (CT) have been improved for noninvasive coronary artery imaging. We investigated the feasibility of the second specification prototype 256-detector row four-dimensional CT for assessing coronary artery and cardiac function. MATERIALS AND METHODS: The subjects were five patients with coronary artery disease. Contrast medium (40-60 ml) was intravenously administered at the rate of 3-4 ml/s. The patient's whole heart was scanned for 1.5 s to cover at least one cardiac cycle during breathholding without electrocardiographic gating. Parameters used were 0.5 mm slice thickness, 0.5 s/rotation, 120 Kv, and 350 mA, with a half-scan reconstruction algorithm (temporal resolution 250 ms). Twenty-six transaxial datasets were reconstructed at intervals of 50 ms. RESULTS: The assessability of the coronary arteries in AHA segments 1, 2, 3, 5, 6, 7, 9, and 11 was visually evaluated, resulting in 29 of 32 (90.9%) segments being assessable. Functional assessment was also performed using animated movies without banding artifacts in all cases. CONCLUSIONS: The 256-detector row four-dimensional CT can assess the coronary artery and cardiac function using data during 1.5 s without banding artifacts.

Assessment of left ventricular wall motion using 16-channel multislice computed tomography: comparison with left ventriculography.

PURPOSE: Using the raw data from coronary computed tomography (CT) angiography, multislice CT (MSCT) can be used to evaluate cardiac function. However, the accuracy of left ventricular (LV) wall motion assessment by MSCT has not been thoroughly investigated. We investigated whether 16-channel MSCT could accurately assess LV wall motion by comparing its results with those of conventional biplane left ventriculography (LVG). MATERIALS AND METHODS: The study included 20 patients with various kinds of heart disease. All patients underwent both contrast-enhanced MSCT and biplane LVG. Using a retrospective electrocardiography-gating technique, 10 phases over one cardiac cycle were extracted. The left ventricle was divided into seven segments according to the American Heart Association classification. Wall motion was scored as follows: 1, normal; 2, mild to moderate hypokinesis; 3, severe hypokinesis; 4, akinesis; 5, dyskinesis; and 6, aneurysm. The scores obtained by MSCT were compared with those obtained by LVG. The wall motion scores were analyzed using the chi-squared independence test (6 x 6 contingency table). RESULTS: Wall motion could be assessed in all segments of the 20 patients using interactive multiplanar animation. Among a total of 140 segments in 20 patients, scores in 118 were concordant between MSCT and LVG (118/140, 84.3%). CONCLUSION: The 16-MSCT can accurately assess LV wall motion.

Truncation correction of fan beam transmission data for attenuation correction using parallel beam emission data on a 3-detector SPECT system.

BACKGROUND: When the simultaneous transmission computed tomography (TCT)/single photon emission CT (SPECT) acquisition protocol is applied to myocardial studies using a 3-detector SPECT, the narrow effective field of view of a fan beam collimator used for TCT acquisition may cause truncation artifacts on TCT images. In this paper, we propose a new method of correcting for the truncation of TCT. METHODS: The truncated parts of the TCT projection data are corrected using quadratic functions, based on the properties that the integral of non-truncated TCT projection data is constant at any projection angle and the position of the centre of gravity is focused on a fixed point. The usefulness of our method was investigated in phantom and human studies using a 3-detector SPECT equipped with one cardiac fan beam collimator for TCT and two parallel beam collimators for SPECT. We used Tl as a tracer for SPECT and Tc as an external source for TCT. RESULTS: The phantom and human studies showed that our method can adequately correct for the truncation of TCT data acquired using a fan beam collimator in a 3-detector SPECT, as long as there is no truncation in SPECT data. CONCLUSION: Our method appears to be useful for improving the SPECT images obtained using simultaneous TCT/SPECT acquisition in a 3-detector SPECT. However, further studies will be necessary to establish the clinical usefulness of this method.

Assessment of coronary artery and cardiac function using multidetector CT.

Multidetector CT is able to reconstruct artifact-less cardiac images due to improved temporal resolution. In this article, we review the potential benefits of the cardiac application of multidetector CT in the assessment of coronary artery and cardiac function, such as wall motion and systolic thickening. By applying retrospective ECG-gating, 10 phases throughout 1 cardiac cycle are extracted for functional analysis. Animated movies are generated by paging through these 2D and 3D images in cardiac phase order. Left ventricular end-diastolic volume, end-systolic volume, and ejection fraction can also be generated. Using the data acquired during a single breath hold, coronary artery and cardiac function can be assessed by multidetector CT.

Attenuation correction of myocardial SPECT images with X-ray CT: effects of registration errors between X-ray CT and SPECT.

PURPOSE: Attenuation correction with an X-ray CT image is a new method to correct attenuation on SPECT imaging, but the effect of the registration errors between CT and SPECT images is unclear. In this study, we investigated the effects of the registration errors on myocardial SPECT, analyzing data from a phantom and a human volunteer. METHODS: Registerion (fusion) of the X-ray CT and SPECT images was done with standard packaged software in three dimensional fashion, by using linked transaxial, coronal and sagittal images. In the phantom study, an X-ray CT image was shifted 1 to 3 pixels on the x, y and z axes, and rotated 6 degrees clockwise. Attenuation correction maps generated from each misaligned X-ray CT image were used to reconstruct misaligned SPECT images of the phantom filled with 201Tl. In a human volunteer, X-ray CT was acquired in different conditions (during inspiration vs. expiration). CT values were transferred to an attenuation constant by using straight lines; an attenuation constant of 0/cm in the air (CT value = -1,000 HU) and that of 0.150/cm in water (CT value = 0 HU). For comparison, attenuation correction with transmission CT (TCT) data and an external gamma-ray source (99mTc) was also applied to reconstruct SPECT images. RESULTS: Simulated breast attenuation with a breast attachment, and inferior wall attenuation were properly corrected by means of the attenuation correction map generated from X-ray CT. As pixel shift increased, deviation of the SPECT images increased in misaligned images in the phantom study. In the human study, SPECT images were affected by the scan conditions of the X-ray CT. CONCLUSION: Attenuation correction of myocardial SPECT with an X-ray CT image is a simple and potentially beneficial method for clinical use, but accurate registration of the X-ray CT to SPECT image is essential for satisfactory attenuation correction.

Evaluation of the number of SPECT projections in the ordered subsets-expectation maximization image reconstruction method.

Filtered back projection (FBP) method, maximum likelihood-expectation maximization(ML-EM) method, and ordered subsets-expectation maximization (OS-EM) method are currently used for reconstruction of SPECT images in clinical studies. In the ML-EM method, images of good quality can be reconstructed even with a small sampling number of projection data, when compared with FBP. Shorter acquisition time and less radionuclide dose are preferable in the clinical setting if image quality is the same. In this study, we attempted to find optimal conditions for reconstruction of OS-EM images with commonly used sampling numbers of 30, 60 and 120 (step angles: 12 degrees, 6 degrees, and 3 degrees, respectively), with acquisition counts/projection of 30, 60, 120 and 240 each. We adjusted the pixel counts of reconstructed images to be constant, by setting combination of sampling number and counts/projection (120 sampling number for 30 counts/projection, 60 for 60, and 30 for 120). Among the 3 acquisition conditions, the small sampling number of 30 had large acquisition counts per direction, resulting in low signal to noise ratio. Under this condition, the resolution was slightly low, but the uniformity of images was high. The combination of OS-EM and smaller sampling projection number may be clinically useful with reduction of the examination time, which is also beneficial to reduce dead time for gamma-camera rotation.