解凍過程中的動物內臟於死後電腦斷層上的影像表現

Abstract

死後電腦斷層目前在世界多國已普遍應用在法醫領域上，作為協助病理解剖或決定死亡原因及方式的工具。在我國，自2023年3月法醫影像中心成立以來，掃描案件超過450件。因我國在進行死後電腦斷層檢查或病理解剖前的遺體會放置冷凍庫保存，因此常遇到死後電腦斷層檢查時遺體有退冰不完全的情形，造成在電腦斷層影像上出現冷凍退冰的假影，而可能影響影像上的判讀。 本次的研究目的為欲了解冷凍與退冰對死後電腦斷層影像上的影響，及尋找能夠了解遺體掃描時退冰情形的可行方法，未來能夠應用在實務上。 我們針對組織標本和完整動物做實驗，組織標本為豬腦、心、肝、肺、里肌肉、梅花肉及五花肉各5個，完整動物為4公斤小豬2隻的腦、心、肝、左肺、右腎、膀胱及右大腿肌，於攝氏-20度冷凍後，退冰過程中每半小時測量內部溫度、表面溫度和電腦斷層掃描，再分析電腦斷層影像，測量各組織標本ROI的CT值。 從研究結果得到，冷凍後在各豬內臟與豬肉的CT影像上產生低密度區域、在心臟大血管內血液和膀胱內尿液有冰晶和微小氣泡形成，及顱內和肝血管內空氣累積等冷凍假影，肺臟則毛玻璃樣陰影增加。此外，我們也在冷凍後梅花肉和五花肉上看到肌肉組織CT值下降和脂肪組織CT值上升，造成肌肉與脂肪的對比下降的現象。 而在退冰過程中，心臟的CT值最慢回到冷凍前CT值。左肺CT值則在冷凍後及退冰過程中皆持續上升，沒有回到冷凍前的CT值。 心、肝與肺的冷凍（或冷藏）及退冰（或回溫）速度最慢，腦、背肌和大腿肌則較快。在體表溫度部分，完整動物實驗冷凍組中頭與下肢表面溫度上升較快，冷藏組則是腹部表面溫度上升較快。退冰過程中。頭、上腹與下腹的體表溫度與腦、心、肝和膀胱內部溫度之間存在高度線性相關性。在體表溫度和內部溫度與內臟CT值之間在特定溫度區間存在高度線性相關性。在冷凍實驗豬隻退冰過程中，其頭部體表溫度高於11.2度、腹部溫度高於8.8度時或退冰17.5小時後，體內各器官的CT值多已回復到冷凍前的數值。實際將透過測量體表溫度來推測體內是否退冰完全的方法應用在人體身上發現，達到體內完全退冰所需要的體表溫度比本研究得到的結果較高。 本研究是以小豬為實驗對象，且樣本數量較不足，希望之後能更加瞭解人體表面溫度、內臟溫度與內臟CT值之間的關係，並更準確的推測出體內的冷凍和退冰狀態，協助實務上冷凍遺體的應用。

Postmortem computed tomography (PMCT) is widely used in forensic science across many countries as an aid in pathological autopsy or determining the cause and manner of death. In our country, since the establishment of the Forensic Imaging Center in March 2023, over 450 cases have been scanned. Due to the practice of storing bodies in freezers before conducting PMCT or pathological autopsies, incomplete thawing of the bodies often occurs during PMCT examinations, resulting in freeze-thaw artifacts that may affect image interpretation. The purpose of this study is to understand the impact of freezing and thawing on PMCT images and to find feasible methods to assess the thawing status of bodies during scanning, which can be applied in practice. We conducted experiments on tissue specimens and whole animals. Tissue specimens included 5 samples each of pig brain, heart, liver, lung, loin muscle, shoulder blade muscle, and belly muscle. Whole animals included two 4 kg piglets, from which we examined the brain, heart, liver, left lung, right kidney, bladder, and right thigh muscle. After freezing at -20°C, internal temperature, surface temperature, and CT scans were measured every half hour during the thawing process. The CT images were then analyzed, and the CT values of the ROIs (Regions of Interest) in each tissue specimen were measured. The results showed that freezing produced low-density areas in the CT images of the piglet organs and muscle tissues, ice crystals and microbubbles in the blood vessels, the heart and the urinary bladder, and air accumulation in the brain and liver vessels, all of which are freezing artifacts. The lung also showed increased ground-glass opacity. Additionally, we observed decreased CT values in muscle tissues and increased CT values in fat tissues in the shoulder blade muscle and belly muscle, leading to a reduction in the contrast between muscle and fat. During the thawing process, the CT values of the heart returned to their pre-freezing values the slowest. The CT values of the left lung continuously increased during both freezing and thawing, not returning to pre-freezing values. The freezing (or refrigeration) and thawing (or warming) rates of the heart, liver, and lung were the slowest, while those of the brain, back muscle, and thigh muscle were faster. In the whole animal experiments, the surface temperatures of the head and lower limbs increased faster in the freezing group, while the surface temperature of the abdomen increased faster in the refrigeration group. During thawing, there was a high linear correlation between the surface temperatures of the head, upper abdomen, and lower abdomen and the internal temperatures of the brain, heart, liver, and bladder. There was also a high linear correlation between the surface and internal temperatures and the CT values of the internal organs within specific temperature ranges. During the thawing process of frozen experimental pigs, when the surface temperature of the head exceeds 11.2°C and the abdominal temperature exceeds 8.8°C, or after 17.5 hours of thawing, the CT values of various internal organs mostly return to the values they had before freezing. When applying the method of estimating internal thawing status through surface temperature measurement to human bodies, we found that the surface temperature required to achieve complete internal thawing was higher than the results obtained in this study. This study used piglets as experimental subjects, and the sample size was relatively small. We hope to further understand the relationship between human surface temperature, internal organ temperature, and internal organ CT values, and more accurately estimate the freezing and thawing status inside the body to assist in the practical application of frozen bodies in forensic science.