Effect of mechanically simulated diaphragmatic respiratory motion on myocardial SPECT processed with and without attenuation correction.

The goal of this study was to assess the effect of diaphragmatic respiratory motion on inferior wall cold artifact in myocardial SPECT and to assess the ability of attenuation correction (AC) to correct for this artifact in the presence of diaphragmatic motion. METHODS: We used an anthropomorphic phantom with ventricular wall activity, variable ventricular caudal tilt, attenuating liver and spleen cold inserts, and variable vertical (diaphragmatic) motion amplitude and pattern. Cardiac SPECT images were acquired on a gamma camera with dual scanning transmission line sources and commercially available AC software (with scatter correction and iterative reconstruction). The acquired data were processed either using filtered backprojection or with the AC software. The resulting myocardial activity maps were processed with polar plots and with standardized inferior-to-anterior and anterior-to-lateral wall ratios. RESULTS: Subdiaphragmatic attenuation reduces inferior wall counts and this component of inferior wall artifact is fully corrected by AC relative to anterior wall counts both with and without diaphragmatic respiratory motion. In the phantom, diaphragmatic motion artifact manifests as reduction in relative count density in both the anterior wall and the inferior wall relative to the lateral wall, which is not corrected by AC. This artifact becomes more marked with increasing respiratory amplitude and its symmetry depends on the pattern of diaphragmatic motion. CONCLUSION: Images with AC acquired at small respiratory amplitudes (approximately 2 cm) in the phantom resemble images with AC found in published normal patient databases. These results support a clinical need for respiratory gating of myocardial SPECT images.     

Application of pixel truncation to reduce intensity artifacts in myocardial SPECT imaging with Tc-99m tetrofosmin

BACKGROUND: Technetium 99m-labeled radiopharmaceuticals accumulate in the liver and gallbladder, where they generate intensity artifacts that can result in misdiagnosis of myocardial single photon emission computed tomography (SPECT) images. This study identifies and eliminates factors affecting the magnitude and appearance of intensity artifacts in a gallbladder-heart phantom. METHODS AND RESULTS: The myocardium and background compartments of a phantom were filled with Tc-99m at concentrations of 320 and 26.1 kBq/mL, respectively. A disposable plastic syringe containing 5 mL of Tc-99m as a model of the gallbladder was fixed in a position lateral to the heart phantom. Artifact intensity was determined on SPECT images over a specific activity range in the syringe (28.6, 6.6, and 0.2 MBq/mL). Among 72 projection images, those with maximal heart counts in the region of interest were selected. Counts above and below 110% of the maximal heart count in all projection images were excluded and reconstructed, respectively. At 28.6 and 6.6 MBq/mL, excessive artifacts generated cold pixels immediately around the source, whereas lower activity (0.2 MBq/mL) caused the artifacts to disappear. Truncating the counts in the gallbladder caused the intensity artifacts at specific activities of 28.6 and 6.6 MBq/mL to disappear. CONCLUSIONS: The magnitude and appearance of intensity artifacts depend on contrast between extracardiac activities in the same slices of the heart in myocardial SPECT images with Tc-99m tetrofosmin, and pixel truncation can eliminate them.     

Added value of attenuation-corrected Tc-99m tetrofosmin SPECT for the detection of myocardial viability: Comparison with FDG SPECT

BACKGROUND: The aim of this study was to evaluate the value of attenuation correction of technetium 99m tetrofosmin single photon emission computed tomography (SPECT) imaging for the detection of myocardial viability. METHODS AND RESULTS: A head-to-head comparison between resting Tc-99m tetrofosmin SPECT and fluorine 18 fluorodeoxyglucose (FDG) SPECT was performed. Both the noncorrected and attenuation-corrected Tc-99m tetrofosmin SPECT images were compared with the FDG images that served as the reference for viability. Consecutive patients (n = 33) with chronic coronary artery disease and left ventricular dysfunction were included. Segmental Tc-99m tetrofosmin and FDG data were displayed in polar maps (17-segment model), and the segments were normalized to peak activity by use of the 4D-MSPECT software program. Segments with normalized FDG activity greater than 50% were considered viable. A similar cutoff value to assess viability was used for the noncorrected and attenuation-corrected Tc-99m tetrofosmin images. Regional contractile function was determined from the gated Tc-99m tetrofosmin images and scored as normokinesia, hypokinesia, or akinesia/dyskinesia. Of all segments, 482 (85%) were viable on FDG SPECT. Of these, 427 (89%) were classified as viable with noncorrected Tc-99m tetrofosmin. Thus 55 (11%) were underestimated with noncorrected Tc-99m tetrofosmin SPECT; these segments were mainly located in the inferior and inferoseptal regions. Attenuation correction changed the classification of 39 (70%) of the underestimated segments to viable. By use of attenuation correction, the agreement between Tc-99m tetrofosmin and FDG imaging improved from 84% to 90%. Similar observations were made when the analysis was restricted to the dysfunctional segments. CONCLUSION: The addition of attenuation correction to Tc-99m tetrofosmin SPECT significantly improved detection of myocardial viability in patients with chronic coronary artery disease, although minimal underestimation of viability remained as compared with FDG SPECT imaging.     

The volume effect of the stomach on intestinal activity on same-day exercise--rest Tc-99m tetrofosmin myocardial imaging.

PURPOSE: The aim of this study was to investigate quantitatively the volume effect of the stomach on the prevention of intestinal artifacts in the rest phase on same-day exercise--rest Tc-99m tetrofosmin myocardial perfusion scintigraphy. MATERIALS AND METHODS: The study was performed in 81 consecutive patients (43 men, 38 women; mean age, 57 +/- 9 years) who were referred for routine Tc-99m tetrofosmin exercise--rest SPECT myocardial perfusion imaging with normal scintigrams or completely normal inferior wall perfusion on visual assessment of SPECT images. Group A (control group, n = 41) and group B (n = 40) were given 200 ml milk to enhance the hepatobiliary clearance of tetrofosmin 30 minutes before the exercise SPECT acquisition study and just after the injection for the rest SPECT acquisition study. For the rest SPECT acquisition study, patients in group B were given, in addition to milk, a standard solid and fluid meal to enhance the volume of the stomach after the injection of Tc-99m tetrofosmin. In all patients, both exercise and rest SPECT acquisitions were started 45 minutes after the injection of Tc-99m tetrofosmin. Myocardial and abdominal activity were assessed on three separate views in the rest phase of the study, and the mean myocardium-to-abdomen count ratios were calculated. In addition, the presence of interfering intestinal activity was assessed visually on SPECT images. Infracardiac activity was described as absent when it was equal to lung background. RESULTS: The myocardial-to-abdominal ratios were 1.38 +/- 0.05 and 1.95 +/- 0.04 in groups A and B, respectively (P < 0.0001). Interfering intestinal activity with varying degrees of intensity was seen in 20 patients in group A (49%) and in 5 patients in group B (13%; P < 0.001). CONCLUSIONS: These results suggest that filling of the stomach with some fluid and solid food before rest acquisition on the same-day stress--rest protocol, because of its volume effect, may provide a high target-to-nontarget ratio for myocardial imaging and thus may reduce the frequency of intestinal artifacts.     

Gated TI-201 myocardial perfusion SPECT: application of energy window optimization.

PURPOSE: TI-201 scintigraphy is plagued with poor image quality because of the low-energy photons of TI-201 decay. Traditionally, a narrow 20% window centered on 71-72 keV has been used to improve sensitivity. Recent studies indicate that better imaging may be possible by optimizing the energy window to 34% centered on 77 keV. In this study, energy window optimization (EWO) was applied to gated TI-201 myocardial perfusion SPECT, and myocardial functional parameters were compared for gated TI-201 SPECT and gated Tc-99m sestamibi (Tc-99m MIBI) SPECT. METHODS: Count statistics for standard and optimal TI-201 myocardial scintigraphy were noted in 25 patients by assessing the total counts in a mid-ventricular slice of a rest-gated TI-201 myocardial SPECT study. The feasibility of performing functional studies with the application of EWO to TI-201 was assessed using the count statistics of a mid-ventricular slice of an optimized gated TI-201 SPECT study and a gated Tc-99m MIBI SPECT study. The functional parameters (ejection fraction, wall motion, and thickening) of TI-201 with EWO and Tc-99m MIBI were compared in 60 patients who underwent rest-gated TI-201 SPECT followed by poststress gated Tc-99m MIBI SPECT. The left ventricular ejection fraction was calculated using commercially available software, whereas wall thickness and motion were assessed by the consensus of two readers. RESULTS: The application of EWO increased available counts by more than 25%. It also resulted in sufficient counts being available to perform gated TI-201 SPECT without increasing acquisition times or the dose of TI-201. The average ejection fraction was 60.4% for gated TI-201 SPECT and 59.6% for gated Tc-99m MIBI SPECT (not significantly different). Overall, the image quality was rated excellent in 12% for TI-201 and Tc-99m MIBI and good in 50% and 62%, respectively, and poor in 38% and 26%, respectively. CONCLUSION: The application of EWO to TI-201 SPECT allows myocardial functional parameters to be assessed without having to increase the acquisition times or the administered dose of TI-201.     

A comparison of Tl-201 stress-reinjection-prone SPECT and Tc-99m-sestamibi gated SPECT in the differentiation of inferior wall defects from artifacts

The frequency of false positive results obtained from the inferior myocardial region using single photon emission computed tomography (SPECT) myocardial perfusion scintigraphy is significantly higher than that obtained from other regions. Several methods, such as prone-position imaging, have been proposed to overcome this diagnostic problem. The aim of the present study was to compare the results of Tc-99m-sestamibi gated SPECT and Tl-201 prone SPECT in the differentiation of inferior wall artifacts from true defects. For this purpose, 38 subjects, whose coronary anatomies were documented on angiography, underwent same-day stress-rest Tc-99m-sestamibi gated SPECT and Tl-201 stress-reinjection-prone (whose standard supine images demonstrated fixed defects on the inferior wall) SPECT. Gated SPECT was performed by 8 frames per cycle acquisition over a 180 degree rotation on 30 projections. Four gated SPECT slices were obtained on mid-ventricular vertical long axis, horizontal long axis and apical and basal short axis planes, and displayed in cine-format. Both Tl-201 prone imaging and Tc-99m-sestamibi gated analysis increased the specificity of inferior wall disease detection remarkably from 54% to 85% and 46% to 82%, respectively (P<0.05). The difference between diagnostic accuracies was not significant (80% and 82%, respectively) (P > 0.05). The positive predictive values for true defects were 96% for Tl-201 prone imaging and 94% for Tc-99m-sestamibi gated imaging. Based on segmental analysis, the two modalities showed fair agreement (kappa = 0.44 for standard supine protocols, kappa = 0.46 for Tl-201 prone and Tc-99m-sestamibi gated SPECT). It can be concluded that Tc-99m-sestamibi gated SPECT, requiring only two-step acquisition, may potentially increase the test specificity for coronary artery disease (CAD) of the inferior wall as well as does Tl-201 stress-reinjection-prone SPECT. By giving functional information, it seems the most practical method in daily use for supplying the most extensive information about patients with suspected or known CAD.     

Attenuation-corrected 99mTc-MIBI SPECT in overweight patients with chronic ischaemic dysfunction: a comparison to NH3 PET and implications for the diagnosis of myocardial viability

OBJECTIVE: We determined the value of attenuation correction (AC) of myocardial perfusion estimation with (99m)Tc-MIBI SPECT in overweight patients by comparison of uncorrected (filtered back-projection (FBP) and corrected (an iterative algorithm with a measured attenuation coefficients map (FL-AC)) (99m)Tc-MIBI relative uptake to perfusion data obtained in the same patients with NH3 PET. In addition, the impact of attenuation correction for the assessment of myocardial viability with (99m)Tc-MIBI SPECT was determined using FDG PET as the reference method. METHODS: Thirty consecutive overweight patients (BMI=28+/-4) with left ventricular dysfunction underwent a resting (99m)Tc-MIBI SPECT and a PET study (NH3 and FDG). (99m)Tc-MIBI SPECT scans were reconstructed without attenuation correction (FBP) and with attenuation correction (FL-AC). The left ventricle was divided into 16 segments, in which the relative uptake was quantified using circumferential profiles. A relative uptake > or = 60% was considered consistent with viable myocardium for FDG and MIBI. RESULTS: The absolute difference between (99m)Tc-MIBI SPECT and NH3 PET uptakes was less pronounced in the inferior (12+/-10% vs. 17+/-12%, P<0.001), anteroseptal (12+/-11% vs. 16+/-12%, P=0.009) and septal (15+/-12% vs. 18+/-14%, P=0.003) regions (FL-AC vs. FBP, respectively). The sensitivity of MIBI for diagnosing myocardial viability increased from 83 to 100% (P=0.034), without loss in specificity. CONCLUSION: Attenuation correction improves myocardial perfusion estimation by (99m)Tc-MIBI SPECT in the inferior, anteroseptal and septal regions and increases its sensitivity for the diagnosis of myocardial viability.     

Attenuation correction of myocardial SPECT perfusion images with low-dose CT: evaluation of the method by comparison with perfusion PET.

In cardiac SPECT, specificity is significantly affected by artifacts due to photon absorption. As the success of attenuation correction depends mainly on high-quality attenuation maps, SPECT low-dose CT devices are promising. We wanted to evaluate the usefulness of a SPECT low-dose CT device in myocardial perfusion scintigraphy. For the evaluation of attenuation correction systems, primarily comparisons with coronary angiography are used. Because the comparison of a method showing myocardial perfusion with an investigation displaying the morphology of vessels yields some difficulties, we chose perfusion PET with (13)N-ammonia as the reference method. METHODS: We prospectively analyzed 23 patients (6 women, 17 men) with known or suspected coronary artery disease. Rest studies and studies under pharmacologic stress with adenosine were performed. After simultaneous injection of (13)N-ammonia and (99m)Tc-sestamibi, a dynamic PET acquisition was started. The SPECT study was performed about 2 h later. Based on 20-segment polar maps, SPECT with and without attenuation correction was compared with PET-derived perfusion values and ammonia uptake values. The PET uptake images were also smoothed to adjust their resolution to the resolution of the SPECT images. RESULTS: The concordance of SPECT and PET studies was improved after attenuation correction. The main effect was seen in the inferior wall. Especially in the apex and anterolateral wall, there were differences between SPECT and PET studies not attributable to attenuation artifacts. Because these differences diminished after smoothing of the PET studies, they might be due to partial-volume effects caused by the inferior resolution of the SPECT images. CONCLUSION: The x-ray-derived attenuation correction leads to SPECT images that represent myocardial perfusion more accurately than nonattenuation-corrected SPECT images. The benefit of the method is seen primarily in the inferior wall. The low resolution of the SPECT system may lead to artifacts due to partial-volume effects. This phenomenon must be considered when perfusion PET is used as a reference method to investigate the effect of attenuation correction.     

Attenuation corrected gated SPECT for the assessment of left ventricular ejection fraction and volumes

OBJECTIVE: The aim of this study was to evaluate the value of attenuation correction (AC) of Tc-99m tetrofosmin single-photon emission tomography (SPECT) imaging for the assessment of left ventricular ejection fraction (LVEF). METHODS: Attenuation corrected and non-attenuation corrected (NC) resting Tc-99m tetrofosmin SPECT were compared for the assessment of LVEF. Planar multigated radionuclide angiography (MUGA) served as the reference for LVEF assessment. Patients (n = 56) with left ventricular dysfunction who underwent MUGA and rest gated Tc-99m tetrofosmin SPECT within 1 month were included. RESULTS: The average LVEF on NC gated SPECT was 37.4 +/- 11.8% and on AC SPECT 38.5 +/- 13.4% (P = NS). The absolute mean difference of the LVEF between the MUGA and NC gated SPECT and AC gated SPECT was -0.2% (95% CI -1.7 to 1.3) and -1.3% (95% CI -2.7 to 0.03), respectively (P = NS both vs. MUGA). The correlation between NC gated SPECT and AC gated SPECT versus MUGA measurement was high with a correlation coefficient of 0.89 (P < 0.01) and 0.92 (P < 0.01), respectively. End-diastolic volumes (EDVs) and end-systolic volumes (ESVs) were significantly higher with AC gated SPECT when compared with NC gated SPECT (both P < 0.001). CONCLUSIONS: Profile AC gated Tc-99m tetrofosmin SPECT agrees well with MUGA and NC gated Tc-99m tetrofosmin SPECT for the assessment of LVEF. EDVs and ESVs are significantly higher with AC gated SPECT when compared with NC gated SPECT.     

Gated (99m)Tc-tetrofosmin SPECT for discriminating infarct from artifact in fixed myocardial perfusion defects.

Soft-tissue attenuation artifacts generally appear as fixed perfusion-scan defects. Gated (99m)Tc-tetrofosmin SPECT may help differentiate myocardial infarction (MI) from artifacts, as fixed defects with decreased function (wall motion and thickening) probably represent MI, whereas attenuation artifacts represent preserved function. METHODS: Ungated stress and gated rest (99m)Tc-tetrofosmin SPECT was performed on 153 consecutive patients referred for evaluation of coronary artery disease. From stress and summed gated rest images, 107 patients (70%) were identified with isolated fixed defects. The function of the defects was assessed semiquantitatively from gated stress images. The findings were correlated with clinical (history or electrocardiographic Q waves) evidence of MI. RESULTS: Of 62 patients with fixed defects and clinical MI, 60 (97%) had an abnormal defect function. Of 45 patients with no clinical MI, 16 (36%) had decreased function of the defect, possibly indicating silent MI. In 29 of the 45 patients (64%) with no clinical MI, defect function was normal. Because most (90%) fixed defects with normal systolic function occurred in men with inferior fixed defects (87%) or women with anterior fixed defects (3%), these were most likely attenuation artifacts. By reclassifying the condition of patients with fixed defects and normal function as normal, patients with unexplained fixed defects (no clinical MI) decreased from 29% to 10%. CONCLUSION: Gating adds considerable value to (99m)Tc-tetrofosmin SPECT myocardial perfusion imaging in characterizing fixed defects and potentially improves test specificity.     

Completely inverse images in dual-isotope SPECT with TI-201 and I-123 MIBG in a patient with myocarditis

Dual-isotope myocardial SPECT in a female patient with idiopathic myocarditis showed completely inverse images in Tl-201 and I-123 MIBG SPECT. In the dual-isotope SPECT performed 13 days after her admission, Tl-201 SPECT images showed reduced accumulation in the apex and normal accumulation in the other regions, whereas the corresponding I-123 MIBG SPECT images showed normal findings in the apex and reduced uptake in the other regions. These rare discrepancies were due to the difference in photon attenuation of the two isotopes in the apex and denervated-but-viable myocardium in the basal region, which were suggested by the following findings of gated perfusion SPECT and echocardiography. Gated SPECT with Tc-99m tetrofosmin performed 23 days after admission revealed normal myocardial perfusion and normal wall motion. Iodine-123 MIBG SPECT findings reflected impaired wall motion in echocardiography performed on admission, which resembles a phenomenon called "memory image" in coronary artery disease. The present case indicated a pitfall in interpreting dual-isotope imaging.     

Usefulness of dual SPECT with Tc-99m pyrophosphate and Tl-201 to predict further events after acute myocardial infarction with single-vessel coronary artery disease.

PURPOSE: This study was undertaken to determine whether the findings of dual SPECT with Tc-99m pyrophosphate (PYP) and Tl-201 were predictive of further cardiac events after acute myocardial infarction. METHODS: The authors evaluated 88 patients with acute myocardial infarction who underwent dual SPECT for single-vessel coronary artery disease. RESULTS: Twenty-nine patients showed overlapping of Tc-99m PYP and Tl-201 in the same location (overlap-positive group), and 59 patients had no overlap (overlap-negative group). In patients in the overlap-positive group, the incidence of subsequent events was significantly higher than in patients in the overlap-negative group (P < 0.001). In the overlap-positive group, the number of overlap segments in patients with further events was significantly greater than that in patients without further events (P < 0.005). CONCLUSIONS: Areas with overlapping of Tc-99m PYP and Tl-201 may contain jeopardized myocardium. These results suggest that patients who have a Tc-99m PYP and Tl-201 overlap-negative scan are a low risk group, whereas patients who have more overlapping segments may require catheterization and revascularization. Thus simultaneous SPECT imaging with Tc-99m PYP and Tl-201 might be useful to identify patients with greater ischemic risk after acute myocardial infarction.     

Reduction of infracardiac intestinal activity by a small amount of soda water in technetium-99m tetrofosmin myocardial perfusion scintigraphy with adenosine stress

Background  In technetium (Tc)-99m myocardial perfusion imaging (MPI), intestinal activity often interferes with the assessment of myocardial perfusion of the inferior wall. We examined whether a small amount of soda water prevents intestinal activity and improves image quality of the inferior wall in Tc-99m tetrofosmin MPI. Methods and Results  Ninety-five patients referred for 1-day rest/stress Tc-99m tetrofosmin MPI were assigned to one of two groups automatically, according to the data when they underwent MPI: the soda water group (n=63) ingested 100 mL soda water just before image acquisition after adenosine stress, and the control group (n=32) underwent no intervention. The frequency of intestinal activity was assessed visually on planar images. The inferior myocardial wall and the abdominal activity adjacent to the myocardium were assessed quantitatively on three different planar images during stress, and the mean inferior wall-to-abdomen (1/A) count ratio was calculated. The frequency of intestinal activity was 69.8% in the soda water group, and 90.6% in the control group (P=.038). The I/A count ratio was significantly higher in the soda water group than in the control group (1.98±0.51 vs 1.50±0.35, respectively, P<.0001, ±SD). Conclusions  The intake of 100 mL of soda water improves intestinal activity and improves the image quality of the inferior wall.     

Heterogeneity of myocardial wall motion and thickening in the left ventricle evaluated with quantitative gated SPECT

BACKGROUND: Global and regional ventricular function may be evaluated by using gated myocardial perfusion single photon emission computed tomography (SPECT). This study investigated two parameters of regional contraction of the left ventricle, segmental wall motion (WM) and wall thickening (WT), to determine their similarity and disparity in each myocardial segment in patients with normal myocardial perfusion. METHODS AND RESULTS: Thirty-five patients with normal myocardial perfusion and cardiac function (mean left ventricular ejection fraction, 62.6%+/-8.8%) were included in this study. A 1-day stress/rest protocol was used as a means of acquiring technetium 99m (Tc-99m) sestamibi gated SPECT protocol for each patient. A commercially available software package for quantitative gated SPECT (QGS) was used to generate cine loop three-dimensional surface display and SPECT images. The left ventricle was divided into 9 segments to score WM and WT (on a scale of 0 to 4, with 0 being normal and 4 being severely reduced) by 6 independent observers. The WM score was significantly higher than the WT score in the septum, whereas the WM score was lower than the WT score in the inferior segment. Similar WM and WT scores were observed in the remaining segments. CONCLUSIONS: Heterogeneous myocardial WM and WT were observed by using QGS software. These findings suggest that different criteria are required in each segment to evaluate segmental WM and WT by means of gated myocardial perfusion SPECT.     

Myocardial clearance of Tc-99m hexakis-2-methoxy-2-methylpropyl isonitrile (MIBI) in patients with coronary artery disease

Myocardial clearance of the new cationic, lypophilic myocardial perfusion agent, Tc-99m-hexakis-2-methoxy-2-methylpropyl isonitrile (MIBI) was studied in nine patients with coronary artery disease. Regional time-activity curves were determined from serial postexercise myocardial SPECT images after a single dose of Tc-99m MIBI. There were significant differences between the clearance rates from normal and ischemic myocardium. Tc-99m MIBI washout from normal myocardium was 27 +/- 8% by 6 hours after injection. Clearance from mild myocardial defects (initial activity greater than 60% of the activity in normal myocardium) was 16% by 6 hours in six patients. No washout was detected by 6 hours in the three patients with severe myocardial defects. The ratio between the activity in ischemic and normal myocardium increased from 0.70 +/- 0.08 to 0.80 +/- 0.13 and 0.84 +/- 0.13 at 4 and 6 hours after injection in the patients with mild defects. In the patients with large defects, the ratio increased from 0.42 +/- 0.09 to 0.54 +/- 0.07 at 6 hours. It is concluded that, while redistribution is substantially slower than with Tl-201, image interpretation and data evaluation should be approached cautiously when imaging is delayed 4 hours or more after injection of Tc-99m MIBI. Quantitative techniques aimed at evaluating the extent and intensity of myocardial ischemia will be particularly affected.     

Noninvasive diagnosis of cardiac involvement by technetium-99m-pyrophosphate (Tc-99m PYP) myocardial scintigraphy in 2 cases of familial amyloid polyneuropathy and 1 case of secondary amyloidosis

To validate the significance of technetium-99m-pyrophosphate (Tc-99m PYP) myocardial scintigraphy in diagnosing cardiac amyloidosis, 2 patients with familial amyloid polyneuropathy (FAP) and 1 patient with amyloidosis secondary to chronic rheumatic arthritis were studied. All three patients had echocardiographic abnormalities, which were increased wall thickness of the interventricular septum and the left ventricular posterior wall, and granular sparkling appearance in the septum. In 2 patients with FAP, abnormal myocardial uptake of Tc-99m PYP was diffusely detected in Tc-99m PYP SPECT. In the remaining 1 patient with secondary amyloidosis, however, Tc-99m PYP SPECT showed no abnormality, although we had confirmed the presence of myocardial amyloid deposits (type AA amyloid protein) with high amount in the histological examination. Thus, these results indicate that Tc-99m PYP scintigraphy may have a limitation in detecting cardiac involvement in secondary amyloidosis although it is useful in FAP.     

Unusual extracardiac findings detected on myocardial perfusion single photon emission computed tomography studies with Tc-99m sestamibi

The authors describe the incidence and various uptake patterns of Tc-99m sestamibi (MIBI) in the extracardiac area due to unusual causes on myocardial perfusion single photon emission computed tomography (SPECT) studies. Seven patients are presented in whom incidental extracardiac findings were observed during the interpretation of the raw data besides the routine evaluation of myocardial reconstructed SPECT slices. These 7 patients were detected out of 582 consecutive patients (1.2%) who had myocardial perfusion SPECT with Tc-99m MIBI. The findings on the raw data led to additional reconstruction of thoracic SPECT images and eventually detailed examination of the extracardiac area. Two of the patients underwent surgery because of incidental extracardiac findings (thymoma and multinodular goiter) on cardiac scintigraphy. Other causes of increased extracardiac activity were the intestine protruded through the left hemithorax, uptake in the pulmonary arterial wall, and pulmonary interstitial fibrosis due to sarcoidosis. The reasons for decreased Tc-99m MIBI accumulation in the extracardiac area in the 2 other patients were significantly dilated pulmonary arteries and hydatic cyst, which were not defined before to our knowledge. Familiarity with the normal biodistribution and variable uptake patterns in the raw images becomes necessary during the interpretation of myocardial SPECT in order not to miss very unusual incidental extracardiac uptake or information that could lead to alteration in patient management. Potential underlying mechanisms of extracardiac Tc-99m MIBI accumulation are discussed, and the literature about noncardiac Tc-99m MIBI findings detected on myocardial perfusion SPECT studies was reviewed.     

Preliminary report of SPECT imaging with Tc-99m teboroxime in ischemic heart disease.

Tc-99m teboroxime (Cardiotec) is one member of a new class of radiopharmaceuticals, the BATO agents (boronic acid adducts of technetium dioxime). This agent is a small, neutral, lipophilic compound with a high myocardial extraction (approximately 85% to 90%), and its uptake in the heart is directly related to myocardial perfusion. Tc-99m teboroxime washes out rapidly from the heart, and its potential for SPECT imaging has therefore been questioned. Tc-99m teboroxime SPECT imaging was compared prospectively with thallium SPECT (20 of 20 patients) and coronary arteriography (17 of 20 patients) suspected of having coronary artery disease. In this small preliminary series, both Tc-99m teboroxime and thallium SPECT detected all abnormal patients (12 of 12) and predicted correctly the site of critical stenosis in 20 of 24 diseased arteries (83%). Tc-99m teboroxime SPECT was normal in 5 of 6 patients without evidence of disease. Several cases occurred of clearly different radiotracer distribution (not related to obvious artifacts) with teboroxime compared with thallium, and lesion size was significantly larger on teboroxime compared with thallium SPECT. The clinical significance of these differences is not yet clear. Tc-99m teboroxime SPECT is possible with imaging times less than half those of thallium SPECT. Though much work remains to be done, teboroxime, because of its unique kinetics, creates many new possibilities for the evaluation of ischemic heart disease.     

Comparison of nitrate augmented Tc-99m tetrofosmin gated SPECT imaging with FDG PET imaging for the assessment of myocardial viability in patients with severe left ventricular dysfunction

Background

Of various nuclear medicine techniques, F-18/flourodeoxyglucose (FDG) positron emission tomography (PET) is considered as the best modality for the assessment of viable myocardium (VM). In this study, we compared the diagnostic accuracy of nitrate augmented Tc-99m tetrofosmin gated G-single-photon emission computed tomography (SPECT) with FDG PET.

Methods

54 consecutive cases of angiographically proven CAD with severe LV dysfunction were enrolled in the study. The patients underwent Tc-99m tetrofosmin G-SPECT and FDG PET as per the standard protocols and were compared.

Results

SPECT data analysis indicated functional abnormalities in 661/918 myocardial segments. F-18 FDG PET revealed VM in 496/661 segments. The diagnostic accuracy of baseline NAC, postnitrate NAC, baseline AC, and postnitrate AC Tc-99m tetrofosmin SPECT was 84%, 87%, 90%, and 94%, respectively. ?? values for NAC baseline, NAC postnitrate, AC baseline, and AC postnitrate Tc-99m tetrofosmin G-SPECT were 0.65, 0.70, 0.77, and 0.85, respectively. Attenuation correction revealed viability additionally in 46 segments which were non-viable on NAC postnitrate study (P?<?.001). Nitrate augmentation showed viability additionally in 25 segments which were non-viable on AC baseline scan (P?=?.004). On patient-based analysis FDG PET changes the management only in 13% (7/54) of patients.

Conclusions

Nitrate augmented AC Tc-99m tetrofosmin G-SPECT shows excellent (???=?.85) agreement with FDG PET. FDG PET changes management only in 13% of the patients. Tc-99m tetrofosmin G-SPECT being more widely available and cheaper imaging modality can be reliably used to detect VM where FDG PET is not available.     

Underestimation of regional myocardial perfusion with Tc-99m sestamibi single-day rest-stress SPECT: a "drug washout" pitfall?

Myocardial perfusion scintigraphy with a Tc-99m sestamibi single-day SPECT protocol is a widely used technique to examine patients with possible or known coronary artery disease. A 76-year-old man with a clinical history suggestive of ischemic heart disease underwent Tc-99m sestamibi myocardial SPECT imaging with a same-day rest and stress protocol after temporary discontinuation of his current therapy, which included calcium channel and beta blockers and nitrates. The scintigraphic pattern was consistent with an asymptomatic infarction of the posterolateral myocardial wall and periinfarct ischemia. One week later, the patient had a Tc-99m sestamibi myocardial SPECT study at rest without discontinuing therapy, and scintigraphic images showed normalization of the posterolateral wall perfusion defect. The angiographic study showed a 90% stenosis of the circumflex artery. This case suggests that, during a 1-day cardiac SPECT protocol, washout of therapeutic pharmaceuticals may be responsible for underestimation of myocardial rest perfusion in territory supplied by a coronary artery with a critical stenosis.