Comparison of 99mTc-MIBI uptakes on planar images with those in excised rats organs.

The precision with which images reflect tracer uptake in the myocardium has been studied. Additionally, the degree to which Tc methoxyisobutylisonitrile (99mTc-MIBI) in the liver gave the effect to a myocardial image has been examined. After administering Tc-MIBI to normal male rats, we compared the myocardial uptakes obtained using a gamma camera with the actual uptakes in the excised organs. Twenty-nine rats were used. Following imaging, the anterior view at 5, 10, 15, 30, 45, 60, 90 and 120 min after administration of the tracer, uptakes in the heart, lung, liver and blood were estimated with a well-type scintillation counter (WC) and represented as the percentage of the injected dose per gram of tissue (%ID/g). The regions of interest (ROIs) were placed on planar images (PI) and the uptake in each organ was estimated as the percentage of the injected dose per pixel (%ID/pixel). The ratios of PI-to-WC and heart-to-organ were also evaluated. Cardiac uptake with WC was maximum (1.581%+/-1.893%) at 10 min post-injection. On the other hand, that with PI was maximum (1.493%+/-0.598%) at 45 min post-injection, but there were significant differences between both measurements (PI/WC ratio: about 1.0 time). Pulmonary uptake with WC was the maximum at 5 min (0.808%+/-0.015%) post-injection, and decreased gradually. PI measurement showed the maximum value at 45 min (0.760%+/-0.012%). Hepatic uptake with WC was the maximum at 30 min (0.594%+/-0.254%). On the other hand, PI measurement showed the same pattern with WC, but these values were higher value than WC as the whole. PI measurement showed higher uptakes in each organ than WC measurement. It was concluded that uptakes or the heart-to-organ ratio obtained clinically with PI might not represent a value that is always accurate.

Clinical approach to renal study incidental to 99mTc-MDP bone scintigraphy.

In order to investigate the feasibility of the assessment of renal function with 99mTc-MDP, we compared renographical images, renogram patterns and the glomerular filtration rate (GFR) obtained by means of a modified Gates' method and 200 MBq of 99mTc-MDP with those obtained by means of 99mTc-DTPA. Because 19 of 20 patients had malignant tumors in the genitourinary tract, there was no difference between the two tracers in identifying a parenchymal defect corresponding to renal cancer. Of eight patients with hydronephrosis, four had a defect or decreased uptake with a dilated pelvis, whereas the other four had marked radioisotope retention in the renal pelvis or the whole kidney on serial images. There was also no difference between the two tracers in identifying hydronephrosis. Of 38 paired renograms 35 showed the same renogram patterns with both tracers. Of three patients with different renogram patterns, two had hydronephrosis. In 20 patients including three patients with bone metastasis, total GFR and split GFR obtained with both tracers correlated with a correlation coefficient of r = 0.920 (p < 0.001) and r = 0.944 (p < 0.001), respectively. Excluding bone metastasis from the analysis, a linear-regression analysis showed excellent agreement between the two measurements with a correlation coefficient of r = 0.960 (p < 0.001) and r = 0.963 (p < 0.001), respectively. The linear regression equations were Y = 1.009X - 0.111 and Y = 1.034X - 0.714, respectively. In conclusion, 99mTc-MDP can be used as a supplement to evaluate renal function incidental to the survey of bone metastases in patients with malignant tumor.

Comparison of 99mTc-tetrofosmin uptakes on planar images with those in excised rats organs.

UNLABELLED: The radioactivity in the organs adjacent to the heart causes interference with the quantitative assessment of myocardial uptake of tracer on scintigraphy. In order to investigate how much the functions of these organs affect myocardial uptake seen in imaging, we compared the myocardial uptake measured by means of a gamma camera with the actual activity in the excised organs. METHODS: Thirty-three rats were imaged at 5, 10, 15, 30, 45, 60, 90 and 120 min after the administration of 99mTc-tetrofosmin, and % injected dose per pixel (%ID/pixel) for each organ was assessed on planar images (PI measurement). Percent injected dose per gram of tissue (%ID/g) in the heart as well as lungs, liver, gastrointestines and blood was measured by means of a well scintillation counter (WC measurement). Comparison between PI and WC measurements was performed with % uptake, the PI-to-WC ratio and heart-to-organ ratios. RESULTS: Our WC measurement showed an increase in cardiac uptake until 30 min (1.67 +/- 0.31%) postinjection and subsequent gradual decrease, whereas PI measurement showed maximum activity of 1.81 +/- 0.52% at 15 min postinjection. There was a prominent difference between the two measurements, particularly at 10 min, with a PI/WC ratio of about 1.6 times. Our WC measurement showed maximum pulmonary uptake at 15 min (0.87 +/- 0.31%) and a gradual decrease over 15 min, whereas PI measurement showed maximum uptake at 10 min (1.14 +/- 0.38%). There was hardly any variation in activity observed later than at 10 min. Our WC measurement showed hardly any variance in hepatic activity from 5 min (0.77 +/- 0.19%) to 30 min (0.69 +/- 0.27%) with a subsequent gradual decrease. The percent uptake in PI measurement was generally greater than that in WC measurement, and high values were found at 10 min and 15 min with PI/WC ratios of about 3.3 times and 2.3 times, respectively. CONCLUSION: Percent uptakes in PI measurement were greater than those in WC measurement. The difference between the two measurements was prominent in the early phases. The cardiac uptake in PI measurement was significantly greater than that in WC measurement at 10 min. It was considered that this discrepancy between the two measurements was caused by the Compton scatter from the organs adjacent to the heart.

New functional polar maps for estimating regional cardiac function using ECG-gated technetium-99m-tetrofosmin SPECT.

OBJECTIVE: The purpose of this work was to develop functional parameters to analyze regional cardiac function using ECG-gated 99mTc-tetrofosmin SPECT. Our goal was to develop a methodology that used slice thickness correction, the generation of a time-activity curve and a polar map. METHODS: Fourteen normal patients without evidence of coronary artery disease were studied. One hour after intravenous injection of 740-1110 MBq (20-30 mCi) 99mTc-tetrofosmin, ECG-gated SPECT data were acquired by dividing a cardiac cycle into 12 frames. The SPECT data were reconstructed from 11 of 12 frames into 3 views. The reconstruction of these images was repeated after performing slice thickness correction. Excluding the effect of different apex-to-base lengths at any frame during a cardiac cycle, 10 short-axis images with the same slice thickness were obtained. Each short-axis image was divided by 40 radii into 40 segments. The time-activity curve was generated from the total counts included in each segment plus both neighboring segments. Subsequently the curve fitting was performed using the second Fourier function. RESULTS: From fitted curves and their differentials, we calculated end-systolic count, end-diastolic count, percent count increase, uptake, peak contraction rate, peak distention rate and contraction time. CONCLUSION: The functional polar maps visually demonstrated regional myocardial function. This method is expected to be helpful for assessing regional cardiac function using 99mTc-tetrofosmin.

99mTc-tetrofosmin uptake in bone metastases from breast cancer.

99mTc-tetrofosmin myocardial imaging was performed in a 62-year-old woman who had undergone standard radical mastectomy for right breast cancer 6 years ago. Although the result was negative for the ischemic heart disease, it showed abnormal accumulation corresponding to the bone metastases in the spine. We believe that 99mTc-tetrofosmin imaging is helpful in detecting bone metastases from breast cancer.

[A modified method of cardiac functional analysis for ECG gated SPECT: study of functional G-maps].

To evaluate the cardiac function accurately using ECG gated SPECT images, we performed a modified method of cardiac functional analysis (Functional G-maps). One hour after the intravenous injection of 1,110 MBq of 99mTc-tetrofosmin, gated SPECT data was acquired dividing a cardiac cycle into 12 frames. Every short-axis images were usually reconstructed using first 11 of 12 frames. The reconstruction of these images was repeated performing slice thickness correction. Because the apex-to-base length is different at any frame during a cardiac cycle, 10 slices of short-axis images were obtained with the same thickness for each frame. Subsequently each short-axis image was divided by 40 radii, and the time activity curve was generated from the total counts included in each segment plus both neighboring segments. Afterwards the curve fitting was performed using the second reverse Fourier function. From fitted curves and their differentials, we estimated a variety of parameters including Max (End-systolic count), Min (End-diastolic count), %CI (Percent count increase), Uptake, PCR (Peak contraction rate), PDR (Peak distention rate) and CT (Contraction time). In 5 normal subjects, %Max was greater in the anterior and septal regions, whereas %Min was greater in the apex and lateral regions. %CI and %PCR were similarly greater in the septal, anterior and inferior regions. On the other hand, %PDR in the lateral or inferior region was lower than the values in the other regions. In conclusion, this modified method is expected to be useful for accurate assessment of regional cardiac function and myocardial perfusion.

How precisely do SPECT images reflect tracer uptake in myocardial infarction? A comparison of thallium-201 and technetium-99m using a myocardial phantom.

OBJECTIVE: We compared the count ratios of 201TI and 99mTc on SPECT images and the true radioactivity in a myocardial phantom to study how precisely SPECT images reflect tracer uptake in myocardial infarction. METHODS: A defect with 20%, 40% or 60% of normal myocardial radioactivity was placed in the anterior or inferior wall of a myocardial phantom to simulate myocardial infarction. Lung radioactivity was kept at 10% or 30% of normal myocardial radioactivity. The count ratio on short-axis SPECT images was calculated using the circumferential profile curve analysis. RESULTS: The count ratios of 201TI and 99mTc SPECT images with an anterior wall defect was lower than the true radioactivity in the phantom. The count ratio on SPECT images with the inferior wall defect was greater than the true radioactivity for the 20% and 40% defects and lower for the 60% defect. CONCLUSION: SPECT images overestimated decreased perfusion in the anterior wall. SPECT images underestimated decreased perfusion for 20% and 40% perfusion defects in the inferior wall.

Comparison of regional myocardial technetium-99m-MIBI uptake between ECG-gated and ungated SPECT imaging.

UNLABELLED: Technetium-99m-MIBI uptake was compared between ECG-gated and ungated SPECT images in 10 normal subjects and 10 patients with coronary artery disease to investigate the effects of wall motion on regional myocardial uptake. METHODS: Left ventricular ejection fraction (LVEF) and wall motion were evaluated using the first-pass data acquired immediately after injection of 1110 MBq 99mTc-MIBI. A transaxial ungated image was reconstructed with cumulative data during a cardiac cycle. For transaxial gated images, data during a cardiac cycle were divided into eight frames and the first seven frames were used. The lateral/septal ratios for ungated and gated images were obtained using the counts in the ROIs drawn in the lateral and the septal walls. RESULTS: In 10 normal subjects, the lateral/septal ratio for gated increased during end-systole. The mean of the lateral/septal ratio was significantly lower for ungated than for gated (1.025 vs. 1.077, p < 0.05). In patients with septal wall asynergy and a normokinetic lateral wall, the mean of the lateral/septal ratios was significantly lower for ungated than for gated (1.267 vs. 1.325, p < 0.01). CONCLUSION: Ungated SPECT acquisition may underestimate regional myocardial uptake when myocardial wall motion is good, therefore, ECG-gated data should be acquired for accurate assessment of regional myocardial uptake of 99mTc-MIBI.

[ATP radionuclide ventriculography; its usefulness for the evaluation of ischemic heart disease].

To evaluate the usefulness for the detection of ischemic heart disease (IHD), ATP first pass radionuclide ventriculography (RVG) was performed in 10 patients. Coronary angiography was performed in all patients. Among these patients, 2 had single vessel disease, 2 had double vessel disease, 3 had triple vessel disease, and 3 had normal coronary arteries. RVG was performed at rest, then, ATP was infused at the rate of 0.16 mg/kg/min and ATP-RVG was done 4 minutes later. The left ventricular ejection fraction (LVEF) was calculated, and the regional wall motion (RWM) was graded as normal, hypokinesis, akinesis, and dyskinesis. In the patients with coronary artery disease, RWM decreased in 5 of 7 patients and LVEF decreased in 6 of 7 patients by ATP. However, RWM and LVEF did not decrease in the patients with normal coronary arteries. These results suggested that ATP-RVG might provide useful information for the evaluation of IHD.

[Evaluation of I-123-BMIPP myocardial SPECT on the detection of ischemic heart disease by comparing with stress thallium-201 myocardial SPECT].

To evaluate the usefulness of I-123-BMIPP as a tracer of fatty acid metabolism in ischemic heart disease, we performed both rest BMIPP myocardial SPECT and stress thallium-201 (Tl) SPECT in 15 patients with prior myocardial infarction, and compared the segmental findings each other. The abnormality of BMIPP images was more intense than that of Tl redistribution images (Tl-RD) in more than 60% of the abnormal segments. The degree of myocardial uptake of BMIPP was more concordant with that of Tl stress scan (Tl-EX) than with that of Tl-RD. This agreement of the findings between BMIPP and Tl-EX was found more remarkably in the regions of incomplete Tl redistribution or in the collateralized regions. These results revealed that ischemia in the jeopardized regions was able to be detected even by rest BMIPP scan. Abnormal findings in BMIPP were observed in more than 95% of segments with persistent defects or incomplete redistribution in Tl, but observed in only 41 or 45% of segments with complete redistribution. Normal findings in BMIPP were observed in 94% of normal segments in Tl. From these results, we can speculate that abnormal regions in BMIPP may have necrotic or ischemic myocardial tissue and normal regions in BMIPP may not have necrotic tissue. These results suggest that I-123-BMIPP may be available to detect myocardial ischemia or infarction in the clinical study. Additionally, the difference in findings between the early images and the delayed images in rest BMIPP scan was observed with relatively high incidence (14% of regions and 73% of patients). More detailed analysis will be required to reveal the importance of this difference.

[A study on crosstalk correction in dual energy acquisition of 123I-MIBG and 201TlCl in myocardial SPECT].

In the simultaneous dual energy acquisition, energy spectrums of two radionuclides crosstalk each other and this phenomenon is a cause of the poor quality of images. In order to obtain the image of high quality in dual energy acquisition of 123I-MIBG and 201TlCl, a crosstalk correction method was originated. The crosstalk from 201Tl to 123I window (R1) and the crosstalk from 123I to 201Tl window (R2) were determined by the cardiac phantom studies. R1 and R2 showed almost constant value throughout the myocardial wall. The crosstalk correction was performed using R1 and R2. After the crosstalk correction, the defect region placed in the cardiac phantom was detected more clearly both in visual interpretation and in quantitative analysis. The crosstalk correction method with R1 and R2 was applied to some clinical cases. By the crosstalk correction, the quality of image was improved and a false defect caused by crosstalk disappeared in a clinical case. The crosstalk correction was considered to be useful for improving the quality of image on dual energy acquisition.

[Usefulness of thallium-201 myocardial SPECT using dipyridamole infusion combined with low level exercise for the detection of the ischemic heart disease--comparison with SPECT images by maximum physical exercise in the same patients].

To evaluate the usefulness of thallium-201 myocardial SPECT using dipyridamole infusion combined with low level exercise (Dp-method) for the detection of the ischemic heart disease, we performed both Dp-method and maximum physical exercise SPECT (Ex-method) in the same 28 patients, and compared the results obtained by the two methods. In the visual evaluation, the detectability of each stenotic coronary territory by Dp-method tended to be higher than that by Ex-method (accuracy 71% vs 67%). The severity of the defect and the degree of the redistribution were higher by Dp-method than those by Ex-method. In the washout rate (WR) analysis in 14 angina pectoris patients, the detectability (accuracy) by Dp-method was significantly higher than that by Ex-method (86% vs 64%; p less than 0.05). In comparison of mean WR values in normal subjects (10 cases for Dp-method and other 8 cases for Ex-method), mean WR by Dp-method was as high as that by Ex-method and the deviation of WR value among subjects was very small. This was probably due to the effect of the low level exercise. These results suggested that Dp-method was more excellent than Ex-method in the evaluation of the ischemic heart disease, and was a useful method of the daily routine work. The incidence of chest symptom and the electrocardiographic ST-depression was as high by Dp-method as that by Ex-method. The filling defects in Dp-method were thought to be induced not only by the difference in the relative increase of the myocardial perfusion, but also by the myocardial ischemia.

[Reverse redistribution in the stress thallium scan--correlation of coronary blood flow and myocardial damage].

In order to make clear 'reverse redistribution (RR)' phenomenon in stress thallium scan we investigated 477 consecutive patients who were consisted of 74 cases with PTCA (PTCA group), 86 cases with coronary artery bypass graft (CABG group) and 317 cases without any revascularization (N group). RR was detected in 12 cases out of PTCA group (16%), in 11 cases out of CABG group (13%) and in 10 cases out of N group (3.2%), and the incidence of RR in PTCA or CABG group was higher than that of N group (p less than 0.01). In 33 patients with RR the cases without significant coronary artery stenosis were more than those with stenosis (p less than 0.01) and the cases with myocardial damage were more than those without damage (p less than 0.01). In quantitative analysis washout rate at the RR areas showed relatively high value, but it was not significant compared with normal value (53 +/- 9.0% vs. 49 +/- 1.9%). In conclusion, RR had a tendency to appear in the condition of normal myocardium mingled with scar and of sufficient coronary blood flow. The mechanism of the phenomenon was thought to be that initial uptake of thallium in the partially scarred area was as high as in the normal myocardium, but washout of thallium from its remaining normal myocardium is normal or faster so that the defect appears at the myocardium mingled with scar. Therefore existence of reverse redistribution suspects the myocardium mingled with scar and sufficient coronary blood flow to the remaining normal myocardium.