Attenuation correction for cardiac dual-head gamma camera coincidence imaging using segmented myocardial perfusion SPECT.

UNLABELLED: The diagnostic accuracy of cardiac FDG imaging obtained with the dual-head coincidence gamma camera (DHC) is impaired by artifacts induced by nonuniform attenuation. This study proposed a new method (registration and segmentation method for attenuation correction [AC-RS]) to correct these attenuations in the chest region without the need for additional hardware or expensive transmission scanning equipment. METHODS: Before DHC imaging, 99mTc-tetrofosmin SPECT was performed using dual-energy acquisition from both the photopeak and Compton scatter windows. The scatter window images of the 99mTc-tetrofosmin were then registered 3-dimensionally with the cardiac DHC images and segmented into anatomic regions to obtain body and lung contours by applying the optimal threshold method on localized histograms. Theoretic attenuation coefficient values were assigned to the corresponding anatomic regions, and the DHC emission images were reconstructed using these attenuation correction factors. The results were quantitatively evaluated by imaging a cardiac phantom filled with a uniform solution and placed in a chest phantom. Eight nondiabetic subjects were also examined using this technique, and the results were compared with those of measured attenuation-corrected PET images. RESULTS: Use of this technique in phantom and clinical studies decreased the degree of artifacts seen in the inferior wall activity and corrected the emission images. When the results were compared with those of PET scans, the regional relative counts of the uncorrected DHC scan did not correlate with the results of the PET scan. However, the regional relative counts of the AC-RS-corrected DHC scan exhibited a linear correlation with the results of the PET scan (r = 0.73; P < 0.001). CONCLUSION: Reasonably accurate attenuation-corrected cardiac DHC images can be obtained using AC-RS without the need for transmission scanning.

Brain fluorine-18 fluorodeoxyglucose imaging with dual-head coincidence gamma camera: comparison with dedicated ring-detector positron emission tomography.

BACKGROUND AND PURPOSE: Dual-head coincidence gamma camera (DHC) imaging has been proposed as an alternative to dedicated ring-detector positron emission tomography (dr-PET) for clinical fluorodeoxyglucose (FDG) studies. The purpose of this investigation was to assess the quality of DHC images in FDG studies of the human brain. METHODS: Seven healthy volunteers and 12 patients with various cerebral disorders underwent consecutive brain dr-PET and DHC with FDG. All sets of images were compared semiquantitatively using regions of interest. RESULTS: Cortical count ratios to the cerebellum on DHC and dr-PET images did not differ significantly among the volunteers, except in the superior frontal cortex and thalamus. In all studies including those of cerebral disorders, the mean cortical-to-cerebellar ratios of DHC and dr-PET images correlated closely. CONCLUSION: FDG imaging with DHC delineated the metabolic distribution of glucose in the brain as well as dr-PET did, except in the superior frontal cortex and thalamus. Therefore, DHC may be a dedicated cost-effective means of detecting metabolic abnormalities in the brain.

Myocardial glucose metabolism in patients with hypertrophic cardiomyopathy: assessment by F-18-FDG PET study.

In an investigation of myocardial metabolic abnormalities in hypertrophic myocardium, the myocardial glucose metabolism was evaluated with F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET) in 32 patients with hypertrophic cardiomyopathy, and the results were compared with those in 9 patients with hypertensive heart disease. F-18-FDG PET study was performed in the fasting and glucose-loading states. The myocardial regional %dose uptake was calculated quantitatively. The average regional %dose uptake in the fasting state in the patients with asymmetric septal hypertrophy and dilated-phase hypertrophic cardiomyopathy was significantly higher than that in the patients with hypertensive heart disease (0.75 +/- 0.34%, 0.65 +/- 0.25%, and 0.43 +/- 0.22%/100 g myocardium, respectively). In contrast, the average %dose uptake in the glucose-loading state in the patients with asymmetric septal hypertrophy and dilated-phase hypertrophic cardiomyopathy was not significantly different from that in patients with hypertensive heart disease (1.17 +/- 0.49%, 0.80 +/- 0.44% and 0.99 +/- 0.45%, respectively). The patients with apical hypertrophy had also low %dose uptake in the fasting state (0.38 +/- 0.21%) as in the hypertensive heart disease patients, so that the characteristics of asymmetric septal hypertrophy and dilated-phase hypertrophic cardiomyopathy are considered to be high FDG uptake throughout the myocardium in the fasting state. Patients with apical hypertrophy are considered to belong to other disease categories metabolically. F-18-FDG PET study is useful in the evaluation of the pathophysiologic diagnosis of patients with hypertrophic cardiomyopathy.

Serial assessment of denervated but viable myocardium following acute myocardial infarction in dogs using iodine-123 metaiodobenzylguanidine and thallium-201 chloride myocardial single photon emission tomography.

Iodine-123 metaiodobenzylguanidine (mIBG) is taken up by sympathetic nerve endings, allowing scintigraphic imaging of myocardial sympathetic innervation. We investigated the denervated but viable canine myocardium after acute myocardial infarction by serial mIBG and thallium-201 chloride (201TlCl) single photon emission tomography (SPET). In 12 dogs, acute myocardial infarction was produced by ligation of the left circumflex coronary artery. Images of mIBG and thallium SPET were obtained 6 h, 1, 4 and 6 weeks later. The defect size was calculated in percentage points from short axial views, and the 123I-mIBG/201TlCl ratio was determined. The uptake ratio was high at 1 week but gradually decreased. Three dogs were killed at each time point, and tissue samples were obtained from infarcted (both 201TlCl and 123I-mIBG defects), peri-infarcted (123I-mIBG defect and 201TlCl normal) and normal myocardium (both mIBG and 201TlCl normal). The changes in tissue content of noradrenaline in these lesions were measured. Noradrenaline tissue content gradually recovered in the peri-infarcted area. However, no recovery was noted in the infarcted area at 6 weeks. We conclude that sympathetic denervation and re-innervation occur following acute myocardial infarction, and the denervated but viable myocardium could be detected non-invasively by combined mIBG and thallium SPET.

[Comparison of myocardial thallium and beta-methyl iodophenyl pentadecanoic acid (BMIPP) distribution in the cardiomyopathic hamster].

The usefulness of fatty acid imaging in the detection of cardiomyopathy was evaluated by comparing thallium and BMIPP myocardial distribution in Bio 14.6 Syrian Hamster (25 week ages). Autoradiography was performed in 3 using 3.7 MBq (100 microCi) of 125I-BMIPP and 37 MBq (1 mCi) of 201TlCl. In vivo pin-hole imaging was performed in 3 using 37 MBq (1 mCi) of 123I-BMIPP and 37 MBq (1 mCi) of 201TlCl. In all cardiomyopathic hamsters decreased uptake of BMIPP compared to that of thallium was demonstrated. These findings suggest dilated cardiomyopathy is associated with severe focal alteration in the substrate used for the performance of myocardial work. In conclusion, myocardial imaging using BMIPP may be useful for early detection of myocardial degeneration compared to thallium in patients with dilated cardiomyopathy.

[Serial assessment of myocardial thallium perfusion and fatty acid utilization in spontaneously hypertensive rats: assessment by autoradiography and pin-hole imaging].

To evaluate the advantage of free fatty acid imaging on the detection of hypertrophied myocardium, we compared sequentially myocardial thallium and BMIPP (15-(p-iodophenyl)-3-(R,S)-methyl pentadecanoic acid) distribution in spontaneously hypertensive rat (SHR) using dual tracer autoradiography and in vivo pin-hole imaging. Autoradiography and pin-hole imaging showed uniform myocardial distribution of BMIPP and thallium within less than 27 weeks age SHR. In 40 weeks age SHR, thallium myocardial distribution showed uniform, however, BMIPP had focal decreases. Quantitative analysis of pin-hole images showed that myocardial BMIPP and thallium uptake ratio decreased according to the ages of SHR. Our data suggest that hypertension is associated with uniform myocardial perfusion and focal alternation in the substrate used for the performance of myocardial work. Based on the above autoradiographic and in vivo pin-hole imagings, I-123 BMIPP imaging may have a potential for early detection on hypertrophic myocardium compared to thallium perfusion in clinically hypertensive patients.

Fatty acid myocardial imaging using 123I-beta-methyl-iodophenyl pentadecanoic acid (BMIPP): comparison of myocardial perfusion and fatty acid utilization in canine myocardial infarction (occlusion and reperfusion model).

To evaluate the relationship between myocardial perfusion and fatty acid metabolism in canine myocardial infarction, 16 dogs were studied using thallium and 123I-beta-methyl-iodophenyl pentadecanoic acid (BMIPP). Eight dogs (group A) had left anterior coronary arterial occlusion (6 h ligation), 6 dogs (group B) had reperfusion (3 h ligation and 1 h reperfusion) and 2 dogs served as the normal control. Myocardial imaging with BMIPP was excellent, owing to its higher uptake and longer retention in myocardium and rapid blood disappearance in addition to diminished liver and lung uptake. The mean half time value which was generated from the BMIPP myocardial washout curve, was significantly larger in the reperfused myocardium. The gamma camera imaging showed uncoupling of BMIPP and thallium (BMIPP uptake greater than thallium uptake) in five dogs in group B. On the other hand, all dogs in group A had a persistent defect in BMIPP and thallium uptake. Our findings indicate that the combination of BMIPP and thallium for myocardial imaging supply different information about the zone of infarction and ischemia, which may be useful for the assessment of myocardial viability.

Myocardial free fatty acid metabolism of the ischemic heart treated by left ventricular assist device.

Three-beta-methyl-iodophenyl-pentadecanoic acid (BMIPP), a newly developed radiographic probe of metabolic processes in tissue free fatty acid (FFA), was applied to a study analyzing the effect of a left ventricular assist device (LVAD) on impaired dog hearts. The radiographic image obtained with BMIPP was compared with 201thallium chloride (TL) imaging, which indicates tissue perfusion. In the myocardial infarction (MI) model, the BMIPP and TL uptake were equally increased with the use of LVAD in the marginal area of the MI. In another model using the reperfused myocardium after ischemia, the BMIPP and TL uptake were increased in the reperfused area by LVAD pumping. On the other hand, BMIPP uptake in the residual myocardium of both models was decreased by LVAD pumping when compared with TL uptake. This discrepancy between these radiographic tracers in the residual myocardium suggests that tissue metabolic processes may be suppressed as result of a decrease in the energy demand by the myocardium caused by LVAD pumping. The results of this study showed that use of LVADs for the impaired heart improved cell function of "stunned" myocardium and also unloaded the excess work from the residual myocardium as judged by FFA metabolism.