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A Count-Preserved Method to Determine Accurate Radiotracer Concentrations of (superscript 99m)Tc Solutions in a Cardiac Phantom for Experimental (superscript 99m)Tc-MIBI GSPECT Studies

利用計數保留決精確量化心臟假體模擬鎝-99m-MIBI閘門式單光子放射電腦斷層掃描時假體各部位最適當鎝-99m溶液濃度

摘要


背景:利用心臟假體進行核醫造影研究之先決條件在於如何適當的模擬放射藥物在人體中的分佈情形。以往的研究雖曾使用數種不同的放射藥物濃度,但是關於這些藥物濃度的由來及被選用的理由,文獻卻不曾提及。本研究嘗試使用計數保留法來找出在擬人軀幹假體及心臓假體中各部位最適當的的鎝-99m溶液濃度,以模擬鎝-99m-MIBI閘門式單光子放射電腦斷層掃描。 方法:本研究包含23個使用低能量全用途準直儀的正常的dipyridamole-壓力鎝-99m-MIBI閘門式單光子放射電腦斷層掃描。把每個單光子放射電腦斷層掃描的64張平面影像加總起來成為一張,圈選出代表心臟、肝臟及背景的區域,再根據(計數數/秒數/相素數)的公式計算每個區域的計數密度。將計數密度按照休息狀態下8毫居里及壓力狀態下22毫居里的放射藥物劑量加以等比例調整。在擬人軀幹假體及心臟假體注入不同濃度的鎝-99m溶液,心臟假體的心肌部份234.58千貝克/毫升(6.34微居里/毫升);肝臟部份351.87千貝克/毫升(9.51微居里/毫升);心臟假體的心室部份及擬人軀幹假體的其他部份23.31KBq/ml(0.63微居里/毫升),用低能量全用迷準直儀在不同時間進行五次單光子放射電腦斷層掃描,計算各部位的計數密度。由線性迴歸的內插或是外插法推算出假體中最適當的鎝-99m溶液濃度。 結果:休息狀態下,心臟假體的心肌、肝臟及背景部份最適當的鎝-99m溶液濃度分別為71.41千貝克/毫升(1.93微居里/毫升)、12.95千貝克/毫升(0.35微居里/毫升)及1.48千貝克/毫升(0.04微居里/毫升)。壓力狀態下,在心臟假體的心肌、肝臟及背景部份最適當的溶液濃度則分別是318.33千貝克/毫升(8.60微居里/毫升)、68.21千貝克/毫升(1.84微居里/毫升)及6.82千貝克/毫升(0.18微居里/毫升)。 結論:本研究使用計數保留的方法得到擬人軀幹假體及心臟假體的各部位中最適當的鎝-99m溶液濃度。對於使用注入鎝-99m溶液的心臟假體來進行的鎝-99m-MIBI閘門式單光子放射電腦斷層掃描的研究,可以作為有用的參考。

並列摘要


Backgrounds: Cardiac phantom studies utilized to investigate imaging characteristics for determination of optimal imaging parameters rely on appropriate simulation of the radiotracer biodistribution within the human bodies. A variety of radiotracer concentrations have been used for (superscript 99m)Tc phantom studies but the methodologies to obtain those values were not clearly mentioned. We introduce and study a count-preserved method to determine the optimal radiotracer concentrations filled in anthropomorphic torso phantom with cardiac insert by utilizing projection data of (superscript 99m)Tc-MIBI patients. Methods: This study enrolled twenty-three consecutive patients who had normal dipyridamole-stressed (superscript 99m)Tc-MIBI gated myocardial perfusion SPECT (GSPECT) with LEAP collimation. We summed the planar images of each study and defined ROIs corresponding to the heart, liver and background respectively. The count density of each ROI as (counts/second/pixel) was then calculated. The count densities were adjusted proportionally according to radiotracer doses of 8 mCi at rest and 22 mCi at stress respectively. The anthropomorphic torso phantom with cardiac insert was filled with (superscript 99m)Tc solution with different concentration levels; 234.58 KBq/ml (6.34μCi/ml) in the myocardial compartment of the cardiac insert, 351.87 KBq/ml (9.5μCi/ml) in the liver compartment, and 23.31 KBq/ml (0.63μCi/ml) in the ventricular chamber of the cardiac insert and the rest of the anthropomorphic torso phantom. The phantom was imaged with LEAP collimation for 5 times and the count densities for different organs were calculated. The optimal concentrations of (superscript 99m)Tc solution in the phantom were then obtained by interpolation or extrapolation with linear regression. Results: The optimal radiotracer concentrations in the myocardial compartment, liver compartment and background for resting distributions were 71.41 KBq/ml (1.93μCi/ml), 12.95 KBq/ml (0.35μCi/ml), and 1.48 KBq/ml (0.04μCi/mi), The radiotracer concentrations in the myocardial compartment, liver compartment and background for stress distribution were 318.33 KBq/ml (8.60μCi/ml), 68.21 KBq/ml (1.84μCi/ml) and 6.82 KBq/ml (0.18μCi/ml), respectively. Conclusions: We demonstrated a count-preserved method to estimate the optimal radiotracer concentrations in the compartments of anthropomorphic torso phantom with a cardiac insert. To further study imaging parameters of (superscript 99m)Tc-MIBI GSPECT using (superscript 99m)Tc cardiac phantom, these data can provide good references for investigators.

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