Clinical evaluation of 360 degrees and 180 degrees data sampling techniques for transaxial SPECT thallium-201 myocardial perfusion imaging

The most serious controversy regarding the application of transaxial SPECT technology to 201Tl myocardial perfusion imaging is the choice between 360 degrees compared with 180 degrees data sampling techniques. The present study utilized the original 360 degrees sampled raw data of 25 patients who had both SPECT 201Tl myocardial perfusion imaging and coronary angio/ventriculography for back projection reprocessing to accomplish the 360 degrees/180 degrees comparison. The results show a high incidence, 36% (9/25), of false-positive segmental perfusion abnormality and a high incidence, 24% (6/25), of moderate to severe degree of image distortion with the 180 degrees data sampled reconstructed images. These were not observed in the 360 degrees data sampled reconstructed images. The above findings confirmed our previous preliminary conclusion that even though the 180 degrees data sampling technique has the advantage of providing improved image contrast and reduction in acquisition time it is not a reliable technique and should be abandoned. The 360 degrees data sampling is the technique of choice for transaxial SPECT 201Tl myocardial perfusion imaging.     

Automatic drawing of the left epicardial region of interest on thallium 201 scintigraphic images

An algorithm has been written which automatically selects a left epicardial region of interest on 201Tl myocardial images. It accomplishes a radial search from the geometric center of the myocardium. On each of the 30 profiles, the local maximum of the 1st derivative is selected as the epicardial edge. The algorithm has been tested in 40 patients at stress and redistribution. In ten patients, conventional planar images were obtained in three views. In 30 patients conventional short axis tomographic images were obtained after reconstruction of 32 projections acquired over 180 degrees. The rate of success is 97% for both imaging modalities. This procedure is another step towards fully automated assessment of myocardial defects and redistribution.     

Comparison between 360° and 180° data sampling in thallium-201 rest-redistribution single-photon emission tomography to predict functional recovery after revascularization

Whether 360° or 180° imaging should be used in cardiac thallium-201 single-photon emission tomography (SPET) studies to detect coronary artery disease remains controversial. Moreover, the relative diagnostic accuracy of 360° and 180°²⁰¹Tl SPET for the assessment of myocardial viability has never previously been studied. The aim of this study was to perform a direct comparison between 180° and 360° data sampling to detect viable myocardium in patients undergoing revascularization; in order to allow optimal detection of viability a rest-redistribution protocol was used. The²⁰¹Tl results were compared with improvement of regional wall motion abnormalities after the revascularization, which was considered as the gold standard for myocardial viability. Thirty-two patients, scheduled for revascularization, underwent rest-redistribution²⁰¹Tl SPET, using a 360° arc. Raw data along a 180° arc (45° RAO to LPO) were selected from the original 360° data sets (both early an late²⁰¹Tl images). All SPET data were analysed semi-quantitatively using circumferential profiles of the short-axis images; the data were displayed in polar maps. Criteria for viability included percentage²⁰¹Tl redistribution and percentage²⁰¹Tl activity on the late image. Regional wall motion was assessed with two-dimensional echocardiography before and 3 months after revascularization. The sensitivities of 360° and 180° imaging for the prediction of functional recovery were 82% and 89%, respectively, whereas the specificities were 51% and 55%, respectively. The diagnostic accuracy of 360° imaging was 62% and that of 180° imaging 67%. This study shows that 360° and 180° imaging have comparable diagnostic accuracy in the prediction of functional recovery after revascularization. With the newer dual-head gamma camera systems with each detector opposing each other, 360° imaging may be preferred.     

Investigation of causes of geometric distortion in 180 degrees and 360 degrees angular sampling in SPECT

To investigate geometric distortion when 180 degrees or 360 degrees angular sampling techniques are used in single photon emission computed tomography (SPECT), a study of point sources imaged at different positions in a water filled cylindrical phantom, and reconstructed using filtered back projection, was conducted. A simulation study, based upon a serial model of the system point spread function (PSF), was used to investigate the contributions of attenuation, spatial resolution and scatter on distortion of the reconstructed PSFs. To study the geometric distortion in transverse (x-y plane), coronal (x-z plane), and sagittal (y-z plane) sections, the ratios of the full widths at half maximum (FWHM) and full widths at tenth maximum (FWTM) in the x/y, x/z, and y/z directions were calculated for the real and simulated PSFs. These results showed that, in an attenuating medium, there is more distortion of point sources into ovals for 180 degrees than for 360 degrees sampling. The simulation study indicated that the primary cause of geometrical distortion in SPECT studies, is the inconsistency of projections due to variable attenuation and spatial resolution. The impact of scatter on geometric distortion was small as measured by the ratios of FWHMs and FWTMs for PSFs. Attenuation correction applied to acquired PSFs significantly reduced geometric distortion in both 180 degrees and 360 degrees studies. To investigate distortion in extended objects, an Iowa heart phantom was placed inside an Alderson body phantom and 201Tl heart SPECT studies acquired. The phantom images confirmed the conclusion that in transverse sections of 360 degrees studies with arithmetic averaging of opposite views, geometric distortion is reduced compared to 180 degrees. The coronal and sagittal sections were equally distorted in both, the 180 degrees and 360 degrees studies, and the 180 degrees studies yielded better contrast.     

Peritoneal fluid causing inferior attenuation on SPECT thallium-201 myocardial imaging in women

On SPECT thallium images, myocardial left ventricular (LV) anterior wall attenuation due to breast tissue is common in women. In contrast, in men, inferior wall counts are normally decreased compared to anterior counts. The purpose of this report is to describe cases of inferior wall attenuation of counts in women caused by peritoneal fluid, not myocardial disease. Twelve consecutive SPECT thallium myocardial studies performed in women on peritoneal dialysis, being evaluated for kidney transplant, were included in this study. For all studies, 3.5 mCi 201Tl were injected intravenously. Thirty-two images were acquired over 180 degrees (45 degrees RAO progressing to 45 degrees LPO) at 40 sec per stop. SPECT images were reviewed in short axis, horizontal long and vertical long axes. Data were also displayed in "bullseye" format with quantitative comparison to gender-matched normal files. Ten of 12 female patients studied had inferior wall defects on images, confirmed by bullseye display. All patients had approximately 2 liters of peritoneal fluid. Review of planar rotational views showed diaphragm elevation and fluid margin attenuations affecting left ventricular inferior wall. Thus, peritoneal fluid is a cause of inferior attenuation on 201Tl cardiac imaging.     

Creation and characterization of Japanese standards for myocardial perfusion SPECT: database from the Japanese Society of Nuclear Medicine Working Group

Objective Standards for myocardial single-photon emission computed tomography (SPECT) adapted for a Japanese population were not available. The purpose of this study was to create standard files approved by the Japanese Society of Nuclear Medicine and to make known the characteristics of the myocardial perfusion pattern of this population. Methods With the collaboration of nine hospitals, a total of 326 sets of exercise–rest myocardial perfusion images were accumulated from subjects with a low likelihood of cardiac diseases. The normal database included a ^99mTc-MIBI/tetrofosmin myocardial perfusion study with 360° (n = 80) and 180° (n = 56) rotations, ²⁰¹Tl study with 360° (n = 115) and 180° rotations (n = 54) and a dual-isotope study with 360° rotation (n = 27). The projection images were transferred by digital imaging and communications in medicine (DICOM) format and reconstructed and analyzed with polar maps. Results The projection data from multiple centers were successfully transferred to a common format for SPECT reconstruction. When the average values were analyzed using a 17-segment model, myocardial counts in the septal segment differed significantly between 180° and 360° rotation acquisitions. Regional differences were observed between men and women in the inferior and anterior regions. A tracer difference between ^99mTc and ²⁰¹Tl was also observed in some segments. The attenuation patterns differed significantly between subjects from the United States and those from Japan. Conclusions Myocardial perfusion data that were specific for the Japanese population were generated. The normal database can serve a standard for nuclear cardiology work conducted in Japan. All author are members of the JSNM Working Group of Standardization of Myocardial SPECT in a Japanese Population.     

Value of linsidomin in assessing myocardial viability with thallium-201 SPECT.

Myocardial viability can be assessed with rest/24 h redistribution (201)Tl myocardial single photon emission computed tomography (SPECT). The intravenous injection of vasodilators induces an early redistribution of (201)Tl and shortens the total examination time. The aim of this study was to compare the images after injection of linsidomin with the 24 h images. We studied 51 consecutive patients (38 males, 13 females), aged 66+/-11 years, referred for assessment of myocardial viability after acute myocardial infarction. SPECT acquisition at rest (30 projections over 180 degrees, 30 s per projection) was performed 20 min after injection of (201)Tl. A second acquisition (same parameters) was performed 2 min after intravenous injection of linsidomin (2 mg). A delayed acquisition was performed on the following day (50 s per step). Myocardial perfusion at rest was normal in 111 of 255 segments. For the 144 other segments, 24 h images were similar to the images acquired after the injection of linsidomin in 94% of cases (136 of 144 segments). The 24 h images showed partial redistribution that was not present after linsidomin in only eight segments (6%). Injection of linsidomin after rest acquisition can provide a reliable and more rapid assessment of myocardial viability. This very simple protocol (rest/linsidomin (201)Tl myocardial SPECT) can be performed in less than 1 h.     

Correlation between intracoronary 201Tl myocardial scanning, coronary angiography and left ventriculography

One hundred and six patients with angina pectoris who underwent routine coronary angiography and left ventriculography were given intracoronary injection of thallium 201. The myocardial images had excellent resolution because of lack of interference from the background activity. The myocardial images and the left ventriculograms showed 94% correlation. Correlation between scans and EKG was lower. There was no correlation between the degree of coronary artery stenosis and 201Tl scan. Currently, the intracoronary injection of 201Tl at rest does not yield additional information to coronary angiography and left ventriculography.     

Transmission-based scatter correction of 180° myocardial single-photon emission tomographic studies

Meaningful comparison of single-photon emission tomographic (SPET) reconstructions for data acquired over 180° or 360° can only be performed if both attenuation and scatter correction are applied. Convolution subtraction has appeal as a practical method for scatter correction; however, it is limited to data acquired over 360°. A new algorithm is proposed which can be applied equally well to data acquired over 180° or 360°. The method involves estimating scatter based on knowl edge of reconstructed transmission data in combination with a reconstructed estimate of the activity distribution, obtained using attenuation correction with broad beam attenuation coefficients. Processing is implemented for planes of activity parallel to the projection images for which a simplified model for the scatter distribution may be applied, based on the measured attenuation. The appropriate broad beam (effective) attenuation coefficients were determined by considering the scatter buildup equation. It was demonstrated that narrow beam attenuation coefficients should be scaled by 0.75 and 0.65 to provide broad beam attenuation coefficients for technetium-99m and thallium-201 respectively. Using a thorax phantom, quantitative accuracy of the new algorithm was compared with conventional transmission-based convolution subtraction (TDCS) for 360° data. Similar heart to lung contrasts were achieved and correction of 180° data yielded a 10.4% error for cardiac activity compared to 5.2% for TDCS. Contrast for myocardium to ventricular cavity was similarly good for scatter-corrected 180° and 360° data, in contrast to attenuation-corrected data, where contrast was significantly reduced. The new algorithm provides a practical method for correction of scatter applicable to 180° myocardial SPET.     

153Gd衰减校正对心肌显像的影响

目的 探讨^153Gd非均匀衰减校正系统对心肌模型及心肌断层图像的校正效果。方法 应用ADAC Vertex Plus双探头SPECT仪及^153Gd非均匀衰减校正系统。心肌断层模型内分别充满^99Tc^mO4^-370MBq和^201Tl37MBq。心肌显像患者共86例,其中男64例,女22例,分别采用和不采用^153Gd非均匀衰减校正。结果 心肌断层模型^153Gd非均匀衰减校正图像与未校正图像的比较分别用目测法和比值法,结果表明：校正图像质量比未校正图像好,更能反映真实情况。^99Tc^m-甲氧基异丁基异腈（MIBI）的图像校正效果好于^201Tl的图像,临床心肌显像图用目测法比较：^99Tc^m-MIBI有差异的占60.2%,^201Tl有差异的占51.4%。结论 ^153Gd非均匀衰减校正系统对心肌图像的校正效果非常明显;^99Tc^m-MIBI的分辨率好于^201Tl。     

Compartmental modeling of technetium-99m-labeled teboroxime with dynamic single-photon emission computed tomography: comparison with static thallium-201 in a canine model

Di Bella EVR, Ross SG, Kadrmas DJ, et al. Compartmental modeling of technetium-99m-labeled teboroxime with dynamic single-photon emission computed tomography: Comparison with static thallium-201 in a canine model. Invest Radiol 2001;36:178-185.RATIONALE AND OBJECTIVES: A compartmental modeling approach to deriving kinetic parameters from a time series of single-photon emission computed tomography (SPECT) images of technetium-99m-labeled (99mTc-) teboroxime may have value for semiquantitative assessment of myocardial perfusion. This study investigated the value of the kinetic parameters derived from a two-compartment model of 99mTc-teboroxime for measuring myocardial perfusion and compared it with static thallium-201 (201Tl) uptake and microsphere-measured blood flow in dogs. METHODS: Experiments were successfully conducted in 9 of 11 open-chest dogs. During adenosine stress, a single complete set of projections of 201Tl uptake was acquired. 99mTc-teboroxime was then injected during adenosine stress, and a complete set of projections was acquired every 5.7 seconds for 17 minutes. Resting studies were performed on 4 of the animals. All of the projection sets were reconstructed with an iterative algorithm and incorporated corrections for attenuation and the geometric response of the collimators. Regional kinetic parameters (washin and washout) were determined semiautomatically from the time series of reconstructed 99mTc-teboroxime images and registered with microsphere data. Regional washin estimates were compared with 201Tl intensities and myocardial blood flows determined from microspheres. RESULTS: Optimally scaled 99mTc-teboroxime washin parameters and 201Tl uptakes were correlated with microsphere-determined blood flows (r = 0.91, y = 0. 99x + 0.01, and r = 0.92, y = 0.88x + 0.28, respectively). In six of the studies, the left anterior descending coronary artery was occluded, and stress occluded-to-normal (O/N) ratios were calculated. The O/N ratios were 0.32 +/- 0.17 as determined from microspheres injected with 201Tl and 0.38 +/- 0.29 from microspheres injected with 99mTc-teboroxime (P = NS). The O/N ratios were 0.48 +/- 0.16 for static 201Tl uptake and 0.27 +/- 0.21 for 99mTc-teboroxime washin (P < 0.05). CONCLUSIONS: Both 201Tl uptake and 99mTc-teboroxime kinetic parameters were well correlated with flow. The 99mTc-teboroxime washin parameters offer semiquantitative flow values and provide greater defect contrast than can be obtained with 201Tl uptake values.     

201Tl与13N-NH3、18F-FDG PET心肌显像判断存活心肌的对比研究

目的　比较再注射2 0 1T1心肌显像与联合应用13 N NH3 及18F 脱氧葡萄糖 (FDG)心肌PET显像判断存活心肌的临床价值。方法　 2 0例心肌梗死患者 ,行2 0 1T1SPECT负荷、再分布、再注射显像及13 N NH3 、18F FDGPET心肌显像。将左室分成 9个节段 ,以视觉评价法对放射性分布进行 4级评分。获得2 0 1T1SPECT再分布、再注射像及18F FDGPET显像的局部心肌摄取率 (%ID)。结果　PET判定为存活心肌的 48个节段中 ,45个节段 (93.8% ) 2 0 1T1再注射像也判定为存活心肌。在2 0 1T1再分布像示放射性分布严重低下的 2 4个节段 ,2 0 1T1再注射像与PET显像判定存活心肌的一致率为 87.5 % ,其中 37.5 %为存活心肌节段 ,5 0 %为无存活心肌节段。 2种显像方法的 %ID无明显差异 ,且呈显著正相关 (r=0 .72 2 )。结论　再注射2 0 1T1心肌显像判断存活心肌的准确性与PET心肌显像相似 ,有较大的临床应用价值。     

Optimal preprocessing Butterworth-Wiener filter for Tl-201 myocardial SPECT

The optimal frequency characteristic of Butterworth-Wiener filters (BWF) for improving the image quality of 201Tl myocardial SPECT was determined by a phantom experiment. Thirty two projection images of the phantom containing 11.1 MBq of 201Tl with 4 different cold lesions were collected during a 180 degree arc of a gamma camera. A set of the projection images were processed with each of 27 different BWFs, and SPECT images were reconstructed by Shepp-Logan filtered backprojection. The SPECT images were evaluated for their diagnostic ability to visibly detect the cold lesions by four nuclear medicine physicians. The lesion contrasts were used as an adjunctive tool to determine the optimum filter. The optimal combination of the parameters determining BWF characteristics (for the data of about 100 count/pixel at the myocardium) is: 1) cutoff of 0.25/pixel, 2) FWHM of 3 pixels, 3) noise/signal ratio of 0.02. FWHM and noise/signal ratio affected lesion contrast much less than cutoff frequency. Clinical myocardial SPECT images processed with the optimal BWF showed less noise and sharper delineation of the myocardium.     

Improved uniformity in tomographic myocardial perfusion imaging with attenuation correction and enhanced acquisition and processing.

Tissue attenuation results in nonuniform myocardial perfusion images with significant sex differences. New SPECT imaging protocols to correct attenuation are currently under investigation. This study was performed to assess the effects of attenuation correction (AC) on overall image uniformity compared with more conventional imaging protocols in both men and women. METHODS: Thirty-nine patients (19 men, 20 women) with less than a 5% likelihood of coronary artery disease were studied. (99m)Tc-sestamibi studies were acquired with a triple-head scanner equipped with a simultaneous transmission and emission protocol. Four imaging protocols were compared: a 180 degrees acquisition and filtered backprojection reconstruction (FBP), a 360 degrees acquisition and FBP, a 360 degrees acquisition and iterative reconstruction (IT), and a 360 degrees acquisition with IT and AC. Quantitative analysis was performed to evaluate myocardial tracer uniformity for men and women. RESULTS: 180 degrees, 360 degrees FBP, and 360 degrees IT showed sex differences, with decreased tracer concentration in the anterior wall in women and decreased tracer concentration in the inferior wall in men. AC images showed the greatest uniformity (9.9% coefficient of variation for AC versus 12.5% for IT, P < 0.0001), and no statistically significant differences in uniformity were seen between male and female AC studies. CONCLUSION: More uniform myocardial perfusion images were obtained with AC, resulting in images with no differences in uniformity between men and women. These techniques are expected to improve specificity and overall diagnostic accuracy.     

Lung at thin-section CT: influence of multiple-segment reconstruction on image quality

PURPOSE: To evaluate multiple-segment reconstruction to reduce cardiac-motion artifacts on thin-section computed tomographic (CT) images in the lung. MATERIALS AND METHODS: Fifty patients were enrolled in the study. All images were obtained with a scanner capable of 1-second revolution time. Routine lung thin-section CT examination was performed with images reconstructed with bone algorithm. Multiple-segment images reconstructed with lung algorithm were obtained for three levels in the left paracardiac region. Segment images were reconstructed retrospectively with data for 225 degrees rotation rather than the 360 degrees rotation used for a complete scan. To minimize differences resulting from reconstruction algorithms, additional nonsegmented reconstruction was performed with lung algorithm. Three radiologists reviewed each set of images and assigned a quality score. Multiway analysis of variance was performed to compare motion artifact reduction with 225 degrees and 360 degrees reconstructions. RESULTS: Differences were not significant (P >.05) between scores for images reconstructed with bone or lung algorithms. Differences were significant between scores for reconstructed images obtained with the combination of 360 degrees bone and 225 degrees segment algorithms (P <.001) and for those obtained with the combination of 360 degrees lung and 225 degrees segment algorithms (P <.001). CONCLUSION: Multiple-segment reconstruction of lung thin-section CT images is an effective technique for reducing cardiac-motion artifacts without increasing patient dose.     

Differential renal uptake of 201Tl: requirements for acquisition, display and quantification.

Renal uptake of 201Tl may have a role in screening for renal asymmetry in hypertensive patients (HP) who are referred for myocardial scintigraphy. The qualitative aspects of digitized planar images, and quantified differential renal uptake (DRU) of 201Tl were rated by comparing a simple technique (S) for outlining each kidney with an interpolative background subtracted technique (IB). These parameters were assessed in an initial series of patients by varying the length of acquisition (from 1 to 5 min), delay in acquisition (from 10 to 210 min after injection), and image preparation (nine-point smoothing). Six blinded observers rated the quality of coded images. Image quality was improved (P less than 0.01) by increasing the length of acquisition to at least 2 min, by smoothing of the images and by imaging within 2 h of 201Tl injection. Variability in quantification of DRU was suboptimal with acquisition for only 1 min and was more adversely affected with S than with IB. Clinical application of the quantitative technique was assessed in 180 HP and 32 normotensive controls. With IB, the normal range for DRU was slightly greater than for S. The two techniques were comparable in identifying abnormal cases and found 21 +/- 3% (S) and 19 +/- 3% (IB) of HP as lying outside the normal 99% confidence interval. Both quantitative techniques showed excellent agreement with renal angiography (n = 24). Furthermore, preliminary experience with surface markers and with 180 degrees tomography suggests the potential for simultaneous correction for renal depth. These data justify the use of adjunctive renal imaging during myocardial scintigraphy with 201Tl.     

Comparison of 180° and 360° acquisition for myocardial perfusion SPECT with compensation for attenuation, detector response, and scatter: Monte Carlo and mathematical observer results

BACKGROUND: The optimal projection data acquisition strategy for myocardial perfusion (MP) single photon emission computed tomography (SPECT) remains controversial. METHODS: We compared MP SPECT using 180 degrees and 360 degrees projection data obtained with the same acquisition time, reconstructed either with filtered back projection (FBP) or the iterative ordered-subsets expectation maximization (OS-EM) algorithm with various combinations of attenuation, detector response, and scatter compensation using mathematical observers and a myocardial defect detection task. We used Monte Carlo-simulated projection data from a population of 3-dimensional nurbs-based cardiac-torso (NCAT) phantoms with ranges of variability in patient anatomy, organ uptake, defect location, defect size, and noise level based on clinical data. Projection data from 180 degrees and 360 degrees acquisitions were generated by assuming the same acquisition time. After iterative or FBP reconstruction, standard postprocessing methods were applied. For each acquisition and reconstruction method, we optimized the number of iterations and cut-off frequency of the Butterworth filter using the Channelized Hotelling Observer methodology. The optimum set of parameters was that which gave the maximum area under the curve. RESULTS: For both acquisition protocols, OS-EM with compensations provided better performance than FBP or OS-EM without compensation. For FBP, the optimized 180 degrees acquisition provided a statistically significant increase in AUC as compared with optimized 360 degrees acquisition. For OS-EM, the AUCs for 180 degrees were slightly larger than for 360 degrees acquisitions when comparing images reconstructed with the same compensations. However, the differences were smaller and not statistically significant. CONCLUSION: With optimized reconstruction and filtering parameters, 180 degrees acquisition provided a statistically significant improvement over 360 degrees acquisition for FBP reconstruction. However, for OS-EM the differences were small and not statistically significant.     

Initial application of respiratory-gated 201Tl SPECT in pulmonary malignant tumours

AIM: Respiratory-gated thallium-201 chloride (201Tl) single photon emission computed tomography (SPECT) was used in preliminary investigations to reduce the adverse respiratory motion effects observed on standard ungated SPECT images and to obtain reliable fusion images with computed tomography (CT) in patients with malignant lung tumours. METHODS: Fifteen patients with primary lung cancer (n=10) or metastatic lung tumours (n=5) underwent gated SPECT 20 min after intravenous injection of 148 MBq 201Tl, using triple-headed SPECT and laser light respiratory tracking units. Projection data were acquired by a step and shoot mode, with 20 stops over 120 degrees for each detector and a preset time of 30 s for each 6 degrees stop. Gated end-inspiratory and ungated images were obtained from 1/8 data centred at peak inspiration for each regular respiratory cycle and for the full respiratory cycle data, respectively. The degree and size of tumour 201Tl uptake were compared between these images by regions of interest (ROI) analysis. Gated SPECT images were registered with rest inspiratory CT images using an automated three-dimensional (3D) image registration tool. Registration mismatch was assessed by measuring the 3D distance of the centroid of 14 201Tl-avid peripheral tumours. Attenuation correction of gated SPECT images was performed using CT attenuation values of these fusion images. RESULTS: Gated SPECT images improved image clarity and contrast of tumour 201Tl uptakes compared with ungated images, regardless of the decreased count density due to the use of gated images. The lesion-to-normal (L/N) lung count ratios and ROI size in 18 well-circumscribed 201Tl-avid tumours were significantly higher and smaller on gated images (both P<0.0001). Gated images showed positive 201Tl uptakes in two small peripheral tumours, although negative on ungated images, and demarcated 201Tl-avid tumours from adjacent 201Tl-avid lymph node or surrounding focal 201Tl uptakes caused by other pathology, although these were not clearly demarcated on ungated images. On fusion images, gated images yielded a significantly better SPECT-CT matching compared with ungated images (P<0.0001). Fusion images accurately localized 201Tl uptakes of tumour/lymph node and other focal pathological/physiological conditions. Attenuation-corrected gated SPECT images further facilitated the detection of 201Tl uptake in small or deeply located lesions, with significantly increased L/N ratios. CONCLUSION: Gated SPECT images facilitate the detection of tumour 201Tl uptake and provide reliable SPECT-CT fusion images, which contribute to accurate interpretation and attenuation correction of Tl SPECT images.     

Difference quantitation of planar and tomographic heart scintigrams with identification of segments using reconstructive three-dimensional reference modelling

A patient-specific three-dimensional rotational ellipsoidal shell was reconstructed from planar myocardial scintigrams. This model was homogeneously filled with radioactivity ('ideal') and then projected onto the same planes as the actual scintigrams, including the absorption of heart and background. After normalization and inhomogeneous background correction, the actual and 'ideal' images were compared in order to quantify the myocardial, ischemic and infarcted volumes (difference quantitation). 201Tl defects appeared as hot spots. The a priori three-dimensional model was cut into 14 segments by six planes. Tomographic sectional views in any desired plane made possible the identification of the 14 spatial myocardial segments on slice images for difference quantitation. The orientation of the long axis of the left heart responsible for different inseparable overprojections of segments was accounted for. The mathematics of segmentation and reconstructive three-dimensional modelling is described. Computed examples are given. A total of 624 201Tl scintigrams from 78 patients were analysed according to this method. The results obtained for the myocardial, ischemic and infarcted volumes, the orientation of the left heart's axis in the thorax and the identification of spatial myocardial segments on projected and tomographic images, as well as the global myocardial and background kinetics of 201Tl are discussed. The procedure of reference modelling and difference quantitation might also be useful in other imaging modalities, such as emission-computed tomography, single-photon emission computed tomography, computed tomography or nuclear magnetic resonance.     

Automatic detection and size quantification of infarcts by myocardial perfusion SPECT: clinical validation by delayed-enhancement MRI.

We aimed to validate the accuracy of a new automated myocardial perfusion SPECT quantification based on normal limits for detection and sizing of infarcts, using delayed-enhancement MRI (DE-MRI) as a gold standard. METHODS: Eighty-two immediate (201)Tl rest scans and 26 (201)Tl delayed redistribution scans were compared with resting DE-MRI scans acquired within 24 h of SPECT acquisition. The immediate (201)Tl scans were considered for validation of infarct detection and the delayed (201)Tl scans were considered for infarct sizing. A simplified quantification scheme was used in which defect extent (EXT) and total perfusion deficit (TPD) parameters were derived automatically from SPECT images by comparison with sex-matched normal limits and applying a 3.0 average deviation criterion. The total extent of hyperenhancement expressed as the percentage of the left ventricle was derived from DE-MRI images by visual definition of myocardial contours and defects. DE-MRI and SPECT images were fused in 3 dimensions for visual comparison. Phantom data were also quantified using the same EXT and TPD measures for defects ranging from 5% to 70% of the myocardium. RESULTS: The area under the receiver-operator-characteristic curve for the detection of infarct on immediate rest scans was 0.91 +/- 0.03 for EXT and 0.90 +/- 0.03 for TPD (P = not significant). The sensitivity and specificity for the detection of infarct by EXT on immediate (201)Tl rest scan were 87% and 91%, respectively, with the optimal defect size threshold of 4%. Six of 7 cases with DE-MRI defects < 5% were detected by SPECT. Infarct sizes obtained from DE-MRI correlated well with EXT (slope = 0.94, offset = 3.8%; r = 0.84) and TPD (slope = 0.75, offset = 4.2%; r = 0.85) obtained from delayed SPECT (201)Tl scans. Excellent correlation was observed between the SPECT quantification and the physical defect size for the phantom data. The actual size of the defect was better estimated by EXT (slope = 1.00, offset 1.33%; r = 0.99) than by TPD (slope = 0.79, offset = 1.9%; r = 0.99). CONCLUSION: Automated quantification of the EXT on myocardial perfusion SPECT images can reliably detect infarcts and measure infarct sizes.