Single-photon Emission Computed Tomography Quantification Research Articles

Impact of bone-equivalent solution density in a thoracic spine phantom on bone single-photon emission computed tomography image quality and quantification.

This study aimed to evaluate the effects of dipotassium hydrogen phosphate (K2HPO4) solution density on single-photon emission computed tomography (SPECT) image quality and quantification. We used a JSP phantom containing six cylinders filled with K2HPO4 solutions of varying densities. Computed tomography (CT) was performed, and CT values and linear attenuation coefficients were measured. Subsequently, SPECT images of an SIM2 bone phantom filled with 99mTc with/without K2HPO4 solution were acquired using a SPECT/CT camera. The full width at half maximum (FWHM), percentage coefficient of variation (%CV), recovery coefficient, and standardized uptake value (SUV) were evaluated to investigate the impact of the K2HPO4 solution density. The CT values and linear attenuation coefficients increased with the K2HPO4 solution density. The CT values for cancellous and cortical bones were reflected by K2HPO4 solution densities of 0.15-0.20 and 1.50-1.70g/cm3, respectively. FWHM values were significantly lower with the K2HPO4 solution than those with water alone (18.0 ± 0.9mm with water alone, 15.6 ± 0.2mm with 0.15g/cm3 K2HPO4, and 16.1 ± 0.3mm with 1.49g/cm3 K2HPO4). Although the %CVs showed no significant differences, the recovery coefficients obtained with water alone tended to be slightly lower than those obtained with the K2HPO4 solution. The SUV obtained using the standard density of the K2HPO4 solution differed from that obtained using the optimized density. In conclusion, SPECT image quality and quantification depends on the presence and concentration of the bone-equivalent solution. The optimal bone-equivalent solution density should be used to evaluate the bone image phantoms.

Quantification of SPECT with <sup>99m</sup>Tc-technetryl and of contrast-enhanced MRI scans in survival prognosis of patients with glial brain tumors after combined chemo – radiation treatment

Purpose of study. The possibility of simultaneous and combined use of magnetic resonance imaging (MRI) with paramagnetic contrast enhancement (CE-MRI) and single-photon emission computed tomography (SPECT) with 99mTc-MIBI in assessing the prognosis in patients with glial brain tumors after complex chemo – and radiotherapy treatment was studied.Material and methods. Contrast-enhanced MRI of the brain and SPECT with 99mTc-Technetril were performed in 19 patients who were observed after complex chemoradiotherapy of brain tumors (gliomas of grade 3 and 4). The treatment included remote gamma irradiation and chemotherapy with temozolomide. The radiation dose was 60 Gy (30 fractions of 2 Gy × 1 once a day). The drug Temodal was prescribed in a single dose of 75 mg/sq. m. (120–140 mg) an hour before gamma therapy for up to 40 days (in a total dose of 5000–5900 mg) and in the post – radiation period according to the scheme – 6 courses of the drug for 5 days every 23 days in a single dose of 200 mg/sq.m. (280–400 mg). The total dose of Temodal for 1 course was 1400–2000 mg. In everybody, after the study, the time period of subsequent survival of patients was registered from to the primary health care data.Results. The survival time was over 20 months in case of patients after surgical removal of glial tumor and with subsequent adjuvant chemotherapy if simultaneous low values of “Tumor-to Normal Tissue” index for both 99mTc-Technetryl SPECT and CE-MRI were met, i.e. if < 1,15 for 99mTc-Technetryl SPECT and < 1,19 for CE-MRI. If index “Tumor-to Normal Tissue” was over > 1,25 99mTc-Technetryl SPECT and > 1,35 for CE-MRI then the survival time was below one year. If the “Tumor-to Normal Tissue”ratio on 99mTc-Technetryl SPECT scan was in benefit ranges whereas the on CE-MRI kept itself in high pathologic ranges the survival time was also over 19 months.Conclusion. Thus, the concomitant quantification and fusion of uptake of 99mTc-Technetryl and paramagnetic contrast agents on SPECT and MRI scans provides prognostic data on survival of patients and is worth routine use for therapy control.

Utility of 123I-MIBG Standardized Uptake Value in Patients with Refractory Pheochromocytoma and Paraganglioma.

Objective(s):Single-photon emission computed tomography (SPECT) using metaiodobenzylguanidine (MIBG) is an important diagnostic tool for the treatment of refractory pheochromocytoma and paraganglioma (PPGL). Owing to the difficulty of SPECT quantification, the tumour-to-background ratio (TBR) is used to assess disease activity. However, the utility of TBR is limited owing to the background setting. A quantification technique of SPECT/computed tomography (CT) would facilitate image interpretation. This study aimed to assess the relationship between 123I-MIBG maximum standardized uptake value (SUVmax) and TBR and levels of urinary catecholamines and metabolites in patients with refractory PPGL. Methods:This study included 15 patients with refractory PPGL who underwent 131I-MIBG therapy. Overall, 27 123I-MIBG SPECT/CT images were acquired before and after the therapy. Lesions observed on whole-body images were analysed; the maximum number of lesions per scan was 10. 123I-MIBG SUVmax was semi-automatically calculated using Q. Metrix package (GE Healthcare). TBR was manually calculated according to the following formula: (max count in lesion − max count in background)/max count in background. Background was set in the contralateral area. When a background region of interest could not be set in the area, it was set in the thigh area. Urine was sampled for 24 h to measure catecholamine and metabolite levels. Increases of ≥3-fold were considered abnormal. TBR, 123I-MIBG SUVmax and urinary catecholamine and metabolite levels were compared using linear regression analysis.Results:All patients had MIBG-avid lesions, as seen on 123I-MIBG SPECT/CT. A significant relationship between 123I-MIBG SUVmax and TBR was observed (correlation coefficient [r] =0.84, P < 0.0001). In 27 SPECT/CT examinations, normetanephrine (NMN) level was abnormally increased in 51% (14/27), but other catecholamine and other metabolites were abnormally increased in < 26% (7/27). 123I-MIBG SUVmax strongly correlated with NMN (r=0.76, P < 0.01) and log NMN (r=0.74, P < 0.01).Conclusion: 123I-MIBG SUVmax demonstrated similar trends as TBR and reflected urinary NMN in patients with refractory PPGL. Semi-automatic quantification of SPECT/CT could be a useful tool for the evaluation of disease activity.

Development of an 123I-metaiodobenzylguanidine Myocardial Three-Dimensional Quantification Method for the Diagnosis of Lewy Body Disease.

Objective(s):We recently developed a new uptake index method for 123I-metaiodobenzylguanidine (123I-MIBG) heart uptake measurements by using planar images (radioisotope angiography and planar image) for the diagnosis of Lewy body disease (LBD), including Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). However, the diagnostic accuracy of the uptake index was approximately equal to that of the heart-to-mediastinum ratio (H/M) for the discrimination of the LBD and non-LBD patients. A simple and pain-free uptake index method using 123I-MIBG SPECT images by modifying the uptake index method may show better diagnostic accuracy than the planar uptake index method. We hypothesized that the development of a new uptake index method for the determination of 123I-MIBG using single-photon emission computed tomography (SPECT) imaging would provide a reliable and reproducible diagnostic tool for clinical application. Regarding this, the purpose of this study was to develop a new uptake index method with a simple protocol to determine 123I-MIBG uptake on SPECT.Methods:The 123I-MIBG input function was determined from the input counts of the pulmonary artery, assessed by analyzing the pulmonary artery time-activity curves. The 123I-MIBG output function was obtained from 123I-MIBG SPECT counts on the polar map. The uptake index was calculated through dividing the output function by the input function (SPECT uptake method). For the purpose of the study, 77 patients underwent 123I-MIBG SPECT, with an average of 31.5 min after clinical assessment and injection of the tracer. The H/M values, as well as planar and SPECT uptake indices were calculated, and then correlated with clinical features. Results:According to the results, values obtained for LBD were significantly lower than those for non-LBD in all analyses (P<0.01). The overlap of the H/M values between the LBD and non-LBD cases ranged from 2.06 to 2.50. Furthermore, the overlap in uptake index values between LBD and non-LBD cases in planar image analysis was 1.05-1.29. The SPECT uptake index method showed the least overlap of 1.23-1.25, with the highest value for LBD patients clearly distinguished from the lowest value for the non-LBD patients.Conclusion:The new 123I-MIBG SPECT quantification method, developed by the input counts of the pulmonary artery, clearly distinguished LBD from non-LBD. Therefore, this method may be appropriate for routine clinical study.

Multimodality molecular imaging of the lung.

Lung diseases cause significant morbidity and mortality and lead to high healthcare utilization. However, few lung disease-specific biomarkers are available to accurately monitor disease activity for the purposes of clinical management or drug development. Advances in cross-modal imaging technologies, such as combined positron emission tomography (PET) and magnetic resonance (MR) imaging scanners and PET or single-photon emission computed tomography (SPECT) combined with computed tomography (CT), may aid in the development of noninvasive, molecular-based biomarkers for lung disease. However, the lungs pose particular challenges in obtaining accurate quantification of imaging data due to the low density of the organ and breathing motion. This review covers the basic physics underlying PET, SPECT, CT, and MR lung imaging and presents technical considerations for multimodal imaging with regard to PET and SPECT quantification. It also includes a brief review of the current and potential clinical applications for these hybrid imaging technologies.

Implications of CT noise and artifacts for quantitative 99mTc SPECT/CT imaging

This paper evaluates the effects of computed tomography (CT) image noise and artifacts on quantitative single-photon emission computed-tomography (SPECT) imaging, with the aim of establishing an appropriate range of CT acquisition parameters for low-dose protocols with respect to accurate SPECT attenuation correction (AC). SPECT images of two geometric and one anthropomorphic phantom were reconstructed iteratively using CT scans acquired at a range of dose levels (CTDIvol = 0.4 to 46 mGy). Resultant SPECT image quality was evaluated by comparing mean signal, background noise, and artifacts to SPECT images reconstructed using the highest dose CT for AC. Noise injection was performed on linear-attenuation (μ) maps to determine the CT noise threshold for accurate AC. High levels of CT noise (σ ∼ 200-400 HU) resulted in low μ-maps noise (σ ∼ 1%-3%). Noise levels greater than ∼ 10% in 140 keV μ-maps were required to produce visibly perceptible increases of ∼ 15% in (99m)Tc SPECT images. These noise levels would be achieved at low CT dose levels (CTDIvol = 4 μGy) that are over 2 orders of magnitude lower than the minimum dose for diagnostic CT scanners. CT noise could also lower (bias) the expected μ values. The relative error in reconstructed SPECT signal trended linearly with the relative shift in μ. SPECT signal was, on average, underestimated in regions corresponding with beam-hardening artifacts in CT images. Any process that has the potential to change the CT number of a region by ∼ 100 HU (e.g., misregistration between CT images and SPECT images due to motion, the presence of contrast in CT images) could introduce errors in μ140 keV on the order of 10%, that in turn, could introduce errors on the order of ∼ 10% into the reconstructed (99m)Tc SPECT image. The impact of CT noise on SPECT noise was demonstrated to be negligible for clinically achievable CT parameters. Because CT dose levels that affect SPECT quantification is low (CTDIvol ∼ 4 μGy), the low dose limit for the CT exam as part of SPECT/CT will be guided by CT image quality requirements for anatomical localization and artifact reduction. A CT technique with higher kVp in combination with lower mAs is recommended when low-dose CT images are used for AC to minimize beam-hardening artifacts.

Cellular Bioenergetics Is an Important Determinant of the Molecular Imaging Signal Derived From Luciferase and the Sodium-Iodide Symporter

Molecular imaging is useful for longitudinal assessment of engraftment. However, it is not known which factors, other than cell number, can influence the molecular imaging signal obtained from reporter genes. The effects of cell dissociation/suspension on cellular bioenergetics and the signal obtained by firefly luciferase and human sodium-iodide symporter labeling of cardiosphere-derived cells were investigated. (18)Fluorodeoxyglucose uptake, ATP levels, (99m)Tc-pertechnetate uptake, and bioluminescence were measured in vitro in adherent and suspended cardiosphere-derived cells. In vivo dual-isotope single-photon emission computed tomography/computed tomography imaging or bioluminescence imaging (BLI) was performed 1 hour and 24 hours after cardiosphere-derived cell transplantation. Single-photon emission computed tomography quantification was performed using a phantom for signal calibration. Cell loss between 1 hour and 24 hours after transplantation was quantified by quantitative polymerase chain reaction and ex vivo luciferase assay. Cell dissociation followed by suspension for 1 hour resulted in decreased glucose uptake, cellular ATP, (99m)Tc uptake, and BLI signal by 82%, 43%, 42%, and 44%, respectively, compared with adherent cells, in vitro. In vivo (99m)Tc uptake was significantly lower at 1 hour compared with 24 hours after cell transplantation in the noninfarct (P<0.001; n=3) and infarct (P<0.001; n=4) models, despite significant cell loss during this period. The in vivo BLI signal was significantly higher at 1 hour than at 24 hours (P<0.01), with the BLI signal being higher when cardiosphere-derived cells were suspended in glucose-containing medium compared with saline (PBS). Adhesion is an important determinant of cellular bioenergetics, (99m)Tc-pertechnetate uptake, and BLI signal. BLI and sodium-iodide symporter imaging may be useful for in vivo optimization of bioenergetics in transplanted cells.

Single-photon emission computed tomography quantification of cerebral blood flow before and after carotid endarterectomy

This study evaluated cerebral blood flow (CBF) by quantification and count profiles of hemispheric CBF using123I-IMP SPECT 10 days before and after surgical removal of an unilateral carotid stenosis in eight selected patients. The endarterectomized carotid artery was stenosed 35–90% in diameter, whereas the contralateral carotid artery was virtually normal. Preoperative CBF in the cerebral hemisphere was lower on the stenosed carotid artery side than on the contralateral side in seven of eight cases. After endarterectomy, hemispheric CBF increased on the operated side in six cases, and on the contralateral side in five, although to a lesser degree. The postoperative increase was prominent in cases having carotid stenosis over approximately 80%. These results indicate that the present method is useful in evaluating the intracranial hemodynamics of cases with carotid stenosis, thereby confirming that endarterectomy is effective in improving CBF in cases with a high degree of stenosis.

Usefulness of 99mTc-ECD brain SPECT with voxel-based analysis in evaluation of perfusion changes early after carotid endarterectomy

SummaryBackgroundAssociation between preoperative perfusion pattern and reperfusion after carotid endarterectomy (CEA) is an important yet unexplored topic. Therefore, the aim of our study was to determine whether 99mTc-ECD single-photon emission computed tomography (SPECT) performed before carotid endarterectomy in patients with internal carotid artery (ICA) stenosis may be helpful in predicting early perfusion changes after revascularization.Material/MethodsThe examined group consisted of 30 patients (mean age 67.4±9.6 years) with ICA stenosis who underwent CEA. Infarction was demonstrated on computed tomography (CT) in 12 cases. Brain perfusion SPECT was performed 1–3 days before CEA and 3–5 days after the surgery. Voxel-based analysis was carried out with Brain SPECT Quantification software. For evaluation of preoperative interhemispheric asymmetry of perfusion, the percentage asymmetry index (AI) was calculated. For comparison of perfusion before and after CEA, the percentage relative difference (RD) was computed.ResultsBefore CEA, cerebral hypoperfusion was seen in 26 cases, including 15 participants with normal CT. After CEA, the following changes of perfusion were observed: perfusion increase n=18 (ipsilateral and bilateral), deterioration n=1, mixed patterns n=2, no change n=9. In patients with preoperative ipsilateral hypoperfusion and perfusion increase after CEA, AI correlated significantly with RD (r=0.48, p=0.04).ConclusionsOur results suggest that perfusion increase 3–5 days after CEA is higher in patients with greater ipsilateral asymmetry index. Evaluation of preoperative AI may help to identify patients in whom rapid reperfusion is more likely.

IMAGE QUANTIFICATION FOR RADIATION DOSE CALCULATIONS—LIMITATIONS AND UNCERTAINTIES

Radiation dose calculations in nuclear medicine depend on quantification of activity via planar and/or tomographic imaging methods. However, both methods have inherent limitations, and the accuracy of activity estimates varies with object size, background levels, and other variables. The goal of this study was to evaluate the limitations of quantitative imaging with planar and single photon emission computed tomography (SPECT) approaches, with a focus on activity quantification for use in calculating absorbed dose estimates for normal organs and tumors. To do this we studied a series of phantoms of varying complexity of geometry, with three radionuclides whose decay schemes varied from simple to complex. Four aqueous concentrations of ⁹⁹mTc, ¹³¹I, and ¹¹¹In (74, 185, 370, and 740 kBq mL⁻¹) were placed in spheres of four different sizes in a water-filled phantom, with three different levels of activity in the surrounding water. Planar and SPECT images of the phantoms were obtained on a modern SPECT/computed tomography (CT) system. These radionuclides and concentration/background studies were repeated using a cardiac phantom and a modified torso phantom with liver and "tumor" regions containing the radionuclide concentrations and with the same varying background levels. Planar quantification was performed using the geometric mean approach, with attenuation correction (AC), and with and without scatter corrections (SC and NSC). SPECT images were reconstructed using attenuation maps (AM) for AC; scatter windows were used to perform SC during image reconstruction. For spherical sources with corrected data, good accuracy was observed (generally within ±10% of known values) for the largest sphere (11.5 mL) and for both planar and SPECT methods with ⁹⁹mTc and ¹³¹I, but were poorest and deviated from known values for smaller objects, most notably for ¹¹¹In. SPECT quantification was affected by the partial volume effect in smaller objects and generally showed larger errors than the planar results in these cases for all radionuclides. For the cardiac phantom, results were the most accurate of all of the experiments for all radionuclides. Background subtraction was an important factor influencing these results. The contribution of scattered photons was important in quantification with ¹³¹I; if scatter was not accounted for, activity tended to be overestimated using planar quantification methods. For the torso phantom experiments, results show a clear underestimation of activity when compared to previous experiment with spherical sources for all radionuclides. Despite some variations that were observed as the level of background increased, the SPECT results were more consistent across different activity concentrations. Planar or SPECT quantification on state-of-the-art gamma cameras with appropriate quantitative processing can provide accuracies of better than 10% for large objects and modest target-to-background concentrations; however when smaller objects are used, in the presence of higher background, and for nuclides with more complex decay schemes, SPECT quantification methods generally produce better results.

Quantification of SPECT and PET for Drug Development

Development of a new drug faces multi-faceted sequences in the pipeline. Once a drug candidate is identified, evaluation process can be accelerated by in vivo noninvasive imaging because there is a potential to use a smaller number of animals and human subjects. Radionuclide imaging techniques, such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) are directly translatable imaging modalities that can be used in both animal models of disease and humans. In addition, SPECT and PET provide a highly sensitive means to track radiolabeled drugs, for which the imaging process less likely perturbs biological functions of animals and humans. Quantification of SPECT and PET data when used for drug development is elusive. Often times, in vivo SPECT and PET images of any drug candidate are used as ‘flash’ show-and-tell scenarios while actual data are obtained from ex vivo analyses. However, once the need and the degree of quantification are defined carefully, quantification of SPECT and PET can play an important role in drug development and evaluation processes.

Striatal dopaminergic D(2) receptor density measured by [(123)I]iodobenzamide SPECT in the prediction of treatment outcome of alcohol-dependent patients.

The authors' goal was to study striatal dopaminergic dopamine 2 (D(2)) receptors as a biological marker of early relapse in detoxified alcoholic patients by using [(123)I]iodobenzamide ([123I]IBZM) single photon emission computed tomography (SPECT). The authors performed [(123)I]IBZM SPECT on 21 alcohol-dependent inpatients during detoxification and on nine healthy volunteers, using the ratios of basal ganglia to occipital lobes for SPECT quantification. Depending on treatment outcome 3 months after hospital discharge, patients were determined to be relapsers or nonrelapsers. Alcohol-dependent subjects with early relapse (within 3 months after hospital discharge) showed a higher uptake of [(123)I]IBZM in the basal ganglia during detoxification (mean ratio=1.83, SD=0.9) than patients who did not have early relapse (mean ratio=1.69, SD=0.11). These results suggest that low levels of dopamine, or an increased density of free striatal dopaminergic D(2) receptors, could be related to early relapse in alcohol-dependent patients. Therefore, [(123)I]IBZM SPECT could become a biological marker of vulnerability to relapse for alcoholic patients in recovery.

Validation of the cerebellum as a reference region for SPECT quantification in patients suffering from dementia of the Alzheimer type

In longitudinal brain studies of dementia of the Alzheimer type (DAT), the cerebellum is often used as a reference region for single photon emission computed tomography (SPECT) quantification, which assumes no significant regional influence of physiological fluctuations or pathology. With the use of absolute quantification in DAT patients, reproducibility of cerebellar uptake of technetium-99m- d,l-hexamethylpropyleneamine oxime (HMPAO) was tested and compared with the mean absolute cerebellar tracer uptake value in DAT patients and healthy control subjects. In 13 DAT patients SPECT studies were repeated within 2 weeks to assess reproducibility of cerebellar regional brain uptake (rBU). With calibrated point sources as scaling factors, cerebellar activity was expressed as rBU of HMPAO per cm 3 brain tissue in percent of the injected lipophilic dose of 740 MBq (20 mCi). Also, mean cerebellar rBU in patients suffering from DAT was calculated and compared with a previously established database obtained in healthy volunteers. Repeated SPECT studies within a 2-week interval in clinically stable patients resulted in a mean rBU increase of 6.8±10.3% in the second SPECT study as compared with the first. A similar shift was previously reported in healthy volunteers. Mean cortical cerebellar rBU values in DAT patients and in the healthy reference population concurred, after cumulative corrections for body surface and for a mean brain volume of 1350 ml (obtained in healthy control subjects), showing respective mean values of 53.9±7.4 and of 52.0±7.3×10 −6 of the injected lipophilic dose 740 MBq (20 mCi) of HMPAO per cm 3 of brain tissue. A unidirectional shift in mean absolute cerebellar uptake values occurs between repeat SPECT examinations in DAT patients similar to previous findings in a group of healthy volunteers. The origin of this phenomenon remains elusive but deserves further study with regard to SPECT (semi)quantification in DAT patients. Most interestingly, the presented findings suggest that with the use of HMPAO SPECT in DAT patients the cerebellum remains scintigraphically uninvolved.

Quantification of SPECT myocardial perfusion images: Methodology and validation of the Yale-CQ method

Background. Quantification of single photon emission computed tomography (SPECT) images is important for reproducible and accurate image interpretation. In addition, SPECT quantification provides important prognostic information. The purpose of this study was to validate the Yale circumferential quantification (Yale-CQ) method in phantom studies. Methods. Myocardial perfusion defects of varying extent and severities were simulated in a cardiac phantom with fillable defect inserts. Forty-five different phantom configurations simulated 45 different myocardial perfusion defect sizes, ranging from 1.6% to 32% of the cardiac phantom volume. Automatic processing was compared with manual processing in the phantom SPECT studies. Results. The automatic Yale-CQ algorithm performed well in all phantom studies. Compared with manual processing, the mean absolute error for automatically determined center of short axis slices was 0.27 pixel in the x direction, 0.45 pixel in the y direction, and 0.15 pixel in radius. Quantification of phantom defects with the Yale-CQ method correlated well with actual defect sizes (R = 0.99), but there was a systematic underestimation (mean error = −7.9%). With derived correction factors the overall correlation between 45 phantom defects and actual defect sizes was excellent, and the estimation error was significantly improved (R = 0.98, mean error = −0.82% for manual method and −0.95% for automatic method). Conclusion. The automatic processing algorithm performs well for the phantom studies. Myocardial perfusion abnormalities can be quantified accurately by use of the Yale-CQ method. Quantified SPECT defect size can be expressed as a percentage of the left ventricle.

Single-photon emission computed tomography quantification of cerebral blood flow before and after carotid endarterectomy

Single-photon emission computed tomography quantification of cerebral blood flow before and after carotid endarterectomy

Technical aspects of myocardial spect imaging with technetium-99m sestamibi

Most reports to date using single photon emission computed tomography (SPECT) with technetium-99m (Tc-99m) sestamibi have used acquisition parameters that were optimized for thallium-201. To fully utilize the superior imaging characteristics of Tc-99m sestamibi, there is a need to optimize the technical aspects of SPECT imaging for this agent. Performance can be enhanced through the careful selection of optimal radiopharmaceutical doses, imaging sequences, acquisition parameters, reconstruction filters, perfusion quantification methods and multidimensional methods for visualizing perfusion distribution. The current report describes theoretical considerations, phantom studies and preliminary patient results that have led to optimized protocols, developed at Emory University and Cedars-Sinai Medical Center, for same-day reststress studies, given existing instrumentation and recommended dose limits. The optimizations were designed to fit a low-dose-high-dose rest-stress same-day imaging protocol. A principal change in the acquisition parameters compared with previous Tc-99m sestamibi protocols is the use of a highresolution collimator. The approach is being developed in both prone and supine positions. A new method for extracting a 3-dimensional myocardial count distribution has been developed that uses spherical coordinates to sample the apical region and cylindrical coordinates to sample the rest of the myocardium. New methods for visualizing the myocardial distribution in multiple dimensions are also described, with improved 2-dimensional, as well as 3- and 4-dimensional (3 dimensions plus time) displays. In the improved 2-dimensional display, distance-weighted and volume-weighted polar maps are used that appear to significantly improve the representation of defect location and defect extent, respectively. The protocols established and the methods developed for acquisition, quantification and display of Tc-99m sestamibi SPECT should provide improved image quality and accuracy, compared to current thallium-201 and Tc-99m sestamibi studies reported to date.

Effects of myocardial wall thickness on SPECT quantification

The effects of changing myocardial wall thickness in single photon emission computed tomography (SPECT) imaging are characterized, and a method which may be used to compensate for these effects is presented. The underlying principle is that the phenomena of attenuation, Compton scatter, and finite resolution can be separated and treated independently. Only finite resolution and its effects, along with a proposed method for correcting these effects, are addressed. A cardiac phantom with varying wall thickness (9-23 mm) was developed to characterize the dependence effects on (201)Tl myocardial SPECT images. Correction factors in the form of recovery coefficients have been developed with the use of a convolution simulation, and are shown to improve substantially the agreement of counts extracted from SPECT images of the phantom with the actual (201)Tl concentration. The degree of improvement, however, is markedly affected by external attenuation. Clinical application of this method will require corrections for attenuation and scatter or the development of regional recovery coefficients which include these effects.