- Email: [email protected]
Frozen (iced) effect on postmortem CT – Experimental evaluation
Journal of Forensic Radiology and Imaging 3 (2015) 210–213
Contents lists available at ScienceDirect
Journal of Forensic Radiology and Imaging journal homepage: www.elsevier.com/locate/jofri
Frozen (iced) effect on postmortem CT – Experimental evaluation Hideki Hyodoh a,n, Keishi Ogura a,b, Miyu Sugimoto a, Yuya Suzuki a, Ayumi Kanazawa a, Rina Murakami a, Junya Shimizu a, Masumi Rokukawa a, Shunichiro Okazaki a, Keisuke Mizuo a, Satoshi Watanabe a a b
Department of Legal Medicine, Sapporo Medical University, S1 W17, Chuo-ku Sapporo 060-8556, Japan Division of Radiology and Nuclear Medicine, Sapporo Medical University, S1 W16, Chuo-ku Sapporo 060-8543, Japan
art ic l e i nf o
a b s t r a c t
Article history: Received 2 September 2015 Received in revised form 20 September 2015 Accepted 5 October 2015 Available online 22 October 2015
The aim of this study is to experimentally evaluate the computed tomography (CT) attenuation of water, saline, iced saline and water ice cubes in order to relate these measurements to low density findings of cadavers on PMCT. Comparing the fluids with the iced materials, the CT number was lower in iced (frozen, with gas) saline (fNaCl) and ice cubes (frozen, without gas) (fH2O) than in saline (NaCl) and tap water (H2O). The fNaCl, which contained small air bubbles, presented significant lower CT number than fH2O. The fNaCl and fH2O showed around 80 HU and the values were concordant with the theoretical result. In cases where low density is found when a cadaver is undergoing a CT examination at low temperature, including the freezing effect as a new differential diagnosis could result in more accurate PMCT interpretation. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Postmortem CT Frozen body Cryoablation Postmortem change Forensic radiology
1. Introduction
2. Materials and methods
As rates of conventional autopsy decline worldwide [1], postmortem computed tomography (PMCT) is increasingly being performed to obtain not only supplementary but also alternatively in selective cases. Legally, PMCT imaging is useful as a non-destructive evaluation with and without traditional autopsy investigation [2–5]. The interpretation of PMCT for making precise diagnosis is difficult without the knowledge of the cadaver's background and postmortem manipulation [6], even if the interpreter has sufficient knowledge and experience in postmortem imaging. O’Donnell et al. [7] reported low density in frozen body and interpreted it as a freezing effect as the corpse was kept refrigerated for transportation. In literature there are scarce publications about thermal effects such as the freezing (iced) effect on PMCT [7] and the influence of body temperature on postmortem MR [8]. The aim of this study is to experimentally evaluate the computed tomography (CT) attenuation of water, saline, iced saline and water ice cubes in order to relate these measurements to low density findings of cadavers on PMCT.
2.1. This study did not need approval by our institutional ethics committee
n
Corresponding author. Fax: þ81 11 611 3935. E-mail address: [email protected] (H. Hyodoh).
http://dx.doi.org/10.1016/j.jofri.2015.10.001 2212-4780/& 2015 Elsevier Ltd. All rights reserved.
To evaluate the frozen effect on PMCT, water and ice were evaluated experimentally. Plastic bottles containing respectively, tap water (H2O), saline (NaCl), iced (frozen, with gas) saline (fNaCl), and a paper cup containing ice cubes (frozen, without gas) (fH2O) were prepared (Fig. 1a). All materials were placed in the same plane on CT.
2.2. Imaging protocol All samples were examined with a 64-slice multi-slice CT scanner (Aquilion CX, Toshiba, Japan) using the following values: 120 kV, 200 mA, 0.5 s/rotation, pitch factor 0.641, configuration 0.5 32, reconstruction 0.5 mm. All of the datasets were stored in the DICOM format. The DICOM data was transferred to a workstation (SYNAPSE VINCENT V4.1, FUJIFILM, Tokyo, Japan). We repeated the image acquisition three times. Placing the region of interest (1.0 cm2) at the center of each image, measurements were repeated six times (Fig. 1b).
H. Hyodoh et al. / Journal of Forensic Radiology and Imaging 3 (2015) 210–213
211
Fig. 1. (a) Macroscopic presentation. All materials are scanned in the same plane. From the left: H2O, fNaCl, NaCl, and fH2O. H2O: tap water, fNaCl: iced (frozen, with gas) saline, NaCl: saline, fH2O: ice cubes (frozen, without gas). (b) CT image with region of interest. To measure the material CT number, the region of interest (1 cm2) was placed at the center of the image and measured 6 times each. From the left: H2O, fNaCl, NaCl, and fH2O. H2O: tap water, fNaCl: iced (frozen, with gas) saline, NaCl: saline, fH2O: ice cubes (frozen, without gas).
2.3. Statistical analysis The JMP (SAS Institute Inc., North Carolina, USA, version 11.0.0) software was used to conduct the Bonferroni/Dunn test for comparisons between each group, and Student's t-test for comparing the ice with and without gas. 3. Results Visual assessment revealed to no distinct difference between
H2O and NaCl – both substances appeared denser than the frozen specimens. fNaCl appeared to be hazy whereas fH2O was translucent. According to the slice thickness, the CT density (mean7S.E.) were as follows: 0.5 mm reconstruction values were 11.278.1 HU in H2O, 79.0 7 10.1 HU in fNaCl, 21.0 78.2 HU in NaCl, and 75.3 78.2 HU in fH2O, and 5.0 mm reconstruction values were 11.17 4.4 HU, 80.8 76.4 HU, 19.9 74.4 HU, and 74.6 75.2 HU, respectively (Table 1). Comparing the fluids with the iced materials, the CT density
212
H. Hyodoh et al. / Journal of Forensic Radiology and Imaging 3 (2015) 210–213
Table 1 CT value (mean7 S.E.) (HU). Reconstruction
H2O
fNaCl
NaCl
fH2O
0.5 mm 5.0 mm
11.2 7 8.1 11.17 4.4
79.0 7 10.1 80.8 7 6.4
21.0 7 8.2 11.9 7 4.4
75.3 7 8.2 74.6 7 5.2
H2O: tap water. fNaCl: iced (frozen, with gas) saline. NaCl: saline. fH2O: ice cubes (frozen, without gas)
was lower in fNaCl and fH2O than in NaCl and H2O (Fig. 2a). The fNaCl, which contained small air bubbles, presented a significantly lower CT density than fH2O (Fig. 2b).
4. Discussion CT density, which is calculated based on the X-ray absorption coefficient [9], was used for the imaging process on CT images. In addition, the CT density shows in proportion to the material's density, unrelated to the material's condition [10]. Consequently, the ice X ray absorption coefficient is 0.92 compared to the water [10]. In results, the CT density of ice was 80 HU in theory. In this study, the fNaCl and fH2O showed around 80 HU and the values were concordant with the theoretical result. In these results, fNaCl presented a lower CT density than fH2O. To avoid contamination, we prepared the fNaCl without opening the bottle's seal. Therefore, the material contained in the ice might be only dissolved air. Comparing the CT density, the fNaCl presented a CT density about 4.5 HU lower. We speculated that this is
due to a partial volume effect of small air bubbles in the voxel. We expect that if iced saline without gas could be prepared, the CT density would show no significant difference compared with fH2O. The mechanism of freezing effect has been reported in clinical cryotherapy [11–13], and mild freezing under 20 °C produces extracellular ice formation [14]. In the frozen cadaver, extracellular ice formation and cold (unfrozen) tissue might be mixed. Therefore, in calculating the CT density, a reflection of the voxel density, the partial volume effect of ice might cause a decrease, resulting in a lower density compared to the non-frozen tissue in the cadaver. Iced tissue is not presented in a living human body except in special physical phenomena of treatment [cryotherapy] [11–13,15]. However, the interpretation of postmortem CT is based on the clinical image interpretation, therefore if there is lack of knowledge of the postmortem process effects on the cadaver, especially the frozen effect, it might lead to misinterpretation of a low density area as fat deposition, or air inclusion. According to our results, water decreased its CT density after solidifying as ice, and this can be the reason body tissue decreases in density. O’Donnell et al. reported the appearance of ice crystals at liver and spleen on PMCT, but not at the brain [7]. We speculated that the tissue containing ratio of fat/water may affect the freezing extent and ice crystals may present with further cooling process. Understanding of the cadaver's condition on postmortem CT is totally different to diagnosing the cause of death. The lower body temperature limit of homeostasis is reported as around 26–30 °C [16]. In case of death by hypothermia, the body presentation was reported as scarlet livor, color difference between the right/left cardiac blood, increased blood sugar, and Wischnewski spots in
Fig. 2. (a) Comparing CT value between the water and ice. The ice shows around 80 HU as its CT number, which is statistically lower than its fluid condition. This phenomenon shows no significant difference according to the reconstruction thickness. H2O: tap water, fNaCl: iced (frozen, with gas) saline, NaCl: saline, fH2O: ice cubes (frozen, without gas). (b) Comparing CT value between ice with and without gas. fNaCl shows lower CT value than fH2O. This phenomenon shows no significant difference according to the reconstruction thickness. fNaCl: iced (frozen, with gas) saline fH2O: ice cubes (frozen, without gas).
H. Hyodoh et al. / Journal of Forensic Radiology and Imaging 3 (2015) 210–213
the mucous membrane of the gastric wall [17]. In addition on PMCT, maintained lung aeration [4], presence of urinary blood [18], and discoloration of joint fluid of the knees and distension of the lung [19] were reported, but not hypodensity of the tissue [7] in the cadaver. In our result, the decreased CT density was not correlated to the cause of death, but enhanced by frozen tissue condition. The partial volume effect might be a cause of the decreasing CT density when the tissue was frozen on CT. There were some limitations in this study. First, this was an ex vivo experimental evaluation, so different circumstances may have effects in the cadaver's PMCT, such as the ratio of fat/air contained in its voxel. Second, the pixel size was minimized according to the CT performance in this study. However, the low density in the cadaver might make it difficult to distinguish an iced tissue from intra-body gas if small particles are contained in the voxel on PMCT. Third, the CT density might show as a similar value in the case of contained fat, due to the partial volume effect. When interpreting postmortem images, background information is required to make a precise diagnosis. Fourth, the accuracy of CT density is the same as the clinical settings, so that the measurement error might exert an effect on the image. In addition, the potential discrepancies of HU measurements as those may be scanner, monitor and parameter dependent. This might affect the discrepancy compared to the theoretical result.
5. Conclusion We experimentally evaluate the freezing (iced) effect and confirmed that the CT density is decreased to around 80 HU. In cases where low density is found when a cadaver is undergoing a CT examination at low temperature, including the freezing effect as a new differential diagnosis could result in more accurate PMCT interpretation.
Acknowledgment We thank Prof. Dr. Myles O’Brien (Mie Prefectual College of Nursy, Tsu, Mie, Japan) for assistance with English Language.
References [1] L. Patriquin, A. Kassarjian, M. Barish, L. Casserley, M. O’Brien, C. Andry, et al., Postmortem whole-body magnetic resonance imaging as an adjunct to autopsy: preliminary clinical experience, J. Magn. Reson. Imaging 13 (2001) 277–287.
213
[2] M.J. Thali, K. Yen, W. Schweitzer, P. Vock, C. Boesch, C. Ozdoba, et al., Virtopsy, a new imaging horizon in forensic pathology: virtual autopsy by postmortem multislice computed tomography (MSCT) and magnetic resonance imaging (MRI)—a feasibility study, J. Forensic Sci. 48 (2003) 386–403. [3] H. Hyodoh, T. Sato, M. Onodera, H. Washio, T. Hasegawa, M. Hatakenaka, Vascular measurement changes observed using postmortem computed tomography, Jpn. J. Radiol. 30 (2012) 840–845. [4] H. Hyodoh, S. Watanabe, R. Katada, K. Hyodoh, H. Matsumoto, Postmortem computed tomography lung findings in fatal of hypothermia, Forensic Sci. Int. 231 (2013) 190–194. [5] H. Hyodoh, J. Shimizu, S. Watanabe, S. Okazaki, K. Mizuo, H. Inoue, Time-related course of pleural space fluid collection and pulmonary aeration on postmortem computed tomography (PMCT), Leg. Med. 17 (2015) 221–225. [6] A. Kanazawa, H. Hyodoh, S. Watanabe, M. Fukuda, M. Baba, S. Okazaki, et al., New pitfalls of high-density postmortem computed tomography, Leg. Med. 16 (2014) 297–299. [7] C. O’Donnell, P. Bedford, M. Burke, Massive hemoperitoneum due to ruptured ectopic gestation: postmortem CT findings in a deeply frozen deceased person, Leg. Med. 13 (2011) 245–249. [8] T.D. Ruder, G.M. Hatch, L. Siegenthaler, G. Ampanozi, S. Mathier, M.J. Thali, et al., The influence of body temperature on image contrast in post mortem MRI, Eur. J. Radiol. 81 (2012) 1366–1370. [9] M.E. Phelps, M.H. Gado, E.J. Hoffman, Correlation of effective atomic number and electron density with attenuation coefficients measured with polychromatic x rays, Radiology 117 (1975) 585–588. [10] T. Kawamura, H. Fukushi, Observation of internal structure in sea ice by X-ray computed tomography, Low Temp. Sci. 45 (1986) 59–67. [11] F.T. Lee Jr., S.G. Chosy, P.J. Littrup, T.F. Warner, J.E. Kuhlman, D.M. Mahvi, CTmonitored percutaneous cryoablation in a pig liver model: pilot study, Radiology 211 (1999) 687–692. [12] S. Permpongkosol, R.E. Link, L.R. Kavoussi, S.B. Solomon, Temperature measurements of the low-attenuation radiographic ice ball during CT-guided renal cryoablation, Cardiovasc. Interv. Radiol. 31 (2008) 116–121. [13] B.C. Allen, E.M. Remer, Percutaneous cryoablation of renal tumors: patient selection, technique, and postprocedural imaging, Radiographics 30 (2010) 887–900. [14] A.A. Gage, J. Baust, Mechanisms of tissue injury in cryosurgery, Cryobiology 37 (1998) 171–186. [15] G.A. Sandison, M.P. Loye, J.C. Rewcastle, L.J. Hahn, J.C. Saliken, J.G. McKinnon, et al., X-ray CT monitoring of iceball growth and thermal distribution during cryosurgery, Phys. Med. Biol. 43 (1998) 3309–3324. [16] P. Saukko, B. Knight, Knight's Forensic Pathology, 3rd edition, 2004. [17] M. Jakubeniene, G.A. Chaker, A. Becelis, D. Malakiene, R. Raudys, Investigation of calcium and sodium in postmortem material as biochemical markers defining the cause of death from hypothermia, Leg. Med. 11 (2009) S304–S306. [18] Y. Kawasumi, N. Onozuka, A. Kakizaki, A. Usui, Y. Hosokai, M. Sato, et al., Hypothermic death: possibility of diagnosis by post-mortem computed tomography, Eur. J. Radiol. 82 (2013) 361–365. [19] W. Schweitzer, M. Thali, G. Giugni, S. Winklhofer, Postmortem pulmonary CT in hypothermia, Forensic Sci. Med. Pathol. 10 (2014) 557–569.
Contents lists available at ScienceDirect
Journal of Forensic Radiology and Imaging journal homepage: www.elsevier.com/locate/jofri
Frozen (iced) effect on postmortem CT – Experimental evaluation Hideki Hyodoh a,n, Keishi Ogura a,b, Miyu Sugimoto a, Yuya Suzuki a, Ayumi Kanazawa a, Rina Murakami a, Junya Shimizu a, Masumi Rokukawa a, Shunichiro Okazaki a, Keisuke Mizuo a, Satoshi Watanabe a a b
Department of Legal Medicine, Sapporo Medical University, S1 W17, Chuo-ku Sapporo 060-8556, Japan Division of Radiology and Nuclear Medicine, Sapporo Medical University, S1 W16, Chuo-ku Sapporo 060-8543, Japan
art ic l e i nf o
a b s t r a c t
Article history: Received 2 September 2015 Received in revised form 20 September 2015 Accepted 5 October 2015 Available online 22 October 2015
The aim of this study is to experimentally evaluate the computed tomography (CT) attenuation of water, saline, iced saline and water ice cubes in order to relate these measurements to low density findings of cadavers on PMCT. Comparing the fluids with the iced materials, the CT number was lower in iced (frozen, with gas) saline (fNaCl) and ice cubes (frozen, without gas) (fH2O) than in saline (NaCl) and tap water (H2O). The fNaCl, which contained small air bubbles, presented significant lower CT number than fH2O. The fNaCl and fH2O showed around 80 HU and the values were concordant with the theoretical result. In cases where low density is found when a cadaver is undergoing a CT examination at low temperature, including the freezing effect as a new differential diagnosis could result in more accurate PMCT interpretation. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Postmortem CT Frozen body Cryoablation Postmortem change Forensic radiology
1. Introduction
2. Materials and methods
As rates of conventional autopsy decline worldwide [1], postmortem computed tomography (PMCT) is increasingly being performed to obtain not only supplementary but also alternatively in selective cases. Legally, PMCT imaging is useful as a non-destructive evaluation with and without traditional autopsy investigation [2–5]. The interpretation of PMCT for making precise diagnosis is difficult without the knowledge of the cadaver's background and postmortem manipulation [6], even if the interpreter has sufficient knowledge and experience in postmortem imaging. O’Donnell et al. [7] reported low density in frozen body and interpreted it as a freezing effect as the corpse was kept refrigerated for transportation. In literature there are scarce publications about thermal effects such as the freezing (iced) effect on PMCT [7] and the influence of body temperature on postmortem MR [8]. The aim of this study is to experimentally evaluate the computed tomography (CT) attenuation of water, saline, iced saline and water ice cubes in order to relate these measurements to low density findings of cadavers on PMCT.
2.1. This study did not need approval by our institutional ethics committee
n
Corresponding author. Fax: þ81 11 611 3935. E-mail address: [email protected] (H. Hyodoh).
http://dx.doi.org/10.1016/j.jofri.2015.10.001 2212-4780/& 2015 Elsevier Ltd. All rights reserved.
To evaluate the frozen effect on PMCT, water and ice were evaluated experimentally. Plastic bottles containing respectively, tap water (H2O), saline (NaCl), iced (frozen, with gas) saline (fNaCl), and a paper cup containing ice cubes (frozen, without gas) (fH2O) were prepared (Fig. 1a). All materials were placed in the same plane on CT.
2.2. Imaging protocol All samples were examined with a 64-slice multi-slice CT scanner (Aquilion CX, Toshiba, Japan) using the following values: 120 kV, 200 mA, 0.5 s/rotation, pitch factor 0.641, configuration 0.5 32, reconstruction 0.5 mm. All of the datasets were stored in the DICOM format. The DICOM data was transferred to a workstation (SYNAPSE VINCENT V4.1, FUJIFILM, Tokyo, Japan). We repeated the image acquisition three times. Placing the region of interest (1.0 cm2) at the center of each image, measurements were repeated six times (Fig. 1b).
H. Hyodoh et al. / Journal of Forensic Radiology and Imaging 3 (2015) 210–213
211
Fig. 1. (a) Macroscopic presentation. All materials are scanned in the same plane. From the left: H2O, fNaCl, NaCl, and fH2O. H2O: tap water, fNaCl: iced (frozen, with gas) saline, NaCl: saline, fH2O: ice cubes (frozen, without gas). (b) CT image with region of interest. To measure the material CT number, the region of interest (1 cm2) was placed at the center of the image and measured 6 times each. From the left: H2O, fNaCl, NaCl, and fH2O. H2O: tap water, fNaCl: iced (frozen, with gas) saline, NaCl: saline, fH2O: ice cubes (frozen, without gas).
2.3. Statistical analysis The JMP (SAS Institute Inc., North Carolina, USA, version 11.0.0) software was used to conduct the Bonferroni/Dunn test for comparisons between each group, and Student's t-test for comparing the ice with and without gas. 3. Results Visual assessment revealed to no distinct difference between
H2O and NaCl – both substances appeared denser than the frozen specimens. fNaCl appeared to be hazy whereas fH2O was translucent. According to the slice thickness, the CT density (mean7S.E.) were as follows: 0.5 mm reconstruction values were 11.278.1 HU in H2O, 79.0 7 10.1 HU in fNaCl, 21.0 78.2 HU in NaCl, and 75.3 78.2 HU in fH2O, and 5.0 mm reconstruction values were 11.17 4.4 HU, 80.8 76.4 HU, 19.9 74.4 HU, and 74.6 75.2 HU, respectively (Table 1). Comparing the fluids with the iced materials, the CT density
212
H. Hyodoh et al. / Journal of Forensic Radiology and Imaging 3 (2015) 210–213
Table 1 CT value (mean7 S.E.) (HU). Reconstruction
H2O
fNaCl
NaCl
fH2O
0.5 mm 5.0 mm
11.2 7 8.1 11.17 4.4
79.0 7 10.1 80.8 7 6.4
21.0 7 8.2 11.9 7 4.4
75.3 7 8.2 74.6 7 5.2
H2O: tap water. fNaCl: iced (frozen, with gas) saline. NaCl: saline. fH2O: ice cubes (frozen, without gas)
was lower in fNaCl and fH2O than in NaCl and H2O (Fig. 2a). The fNaCl, which contained small air bubbles, presented a significantly lower CT density than fH2O (Fig. 2b).
4. Discussion CT density, which is calculated based on the X-ray absorption coefficient [9], was used for the imaging process on CT images. In addition, the CT density shows in proportion to the material's density, unrelated to the material's condition [10]. Consequently, the ice X ray absorption coefficient is 0.92 compared to the water [10]. In results, the CT density of ice was 80 HU in theory. In this study, the fNaCl and fH2O showed around 80 HU and the values were concordant with the theoretical result. In these results, fNaCl presented a lower CT density than fH2O. To avoid contamination, we prepared the fNaCl without opening the bottle's seal. Therefore, the material contained in the ice might be only dissolved air. Comparing the CT density, the fNaCl presented a CT density about 4.5 HU lower. We speculated that this is
due to a partial volume effect of small air bubbles in the voxel. We expect that if iced saline without gas could be prepared, the CT density would show no significant difference compared with fH2O. The mechanism of freezing effect has been reported in clinical cryotherapy [11–13], and mild freezing under 20 °C produces extracellular ice formation [14]. In the frozen cadaver, extracellular ice formation and cold (unfrozen) tissue might be mixed. Therefore, in calculating the CT density, a reflection of the voxel density, the partial volume effect of ice might cause a decrease, resulting in a lower density compared to the non-frozen tissue in the cadaver. Iced tissue is not presented in a living human body except in special physical phenomena of treatment [cryotherapy] [11–13,15]. However, the interpretation of postmortem CT is based on the clinical image interpretation, therefore if there is lack of knowledge of the postmortem process effects on the cadaver, especially the frozen effect, it might lead to misinterpretation of a low density area as fat deposition, or air inclusion. According to our results, water decreased its CT density after solidifying as ice, and this can be the reason body tissue decreases in density. O’Donnell et al. reported the appearance of ice crystals at liver and spleen on PMCT, but not at the brain [7]. We speculated that the tissue containing ratio of fat/water may affect the freezing extent and ice crystals may present with further cooling process. Understanding of the cadaver's condition on postmortem CT is totally different to diagnosing the cause of death. The lower body temperature limit of homeostasis is reported as around 26–30 °C [16]. In case of death by hypothermia, the body presentation was reported as scarlet livor, color difference between the right/left cardiac blood, increased blood sugar, and Wischnewski spots in
Fig. 2. (a) Comparing CT value between the water and ice. The ice shows around 80 HU as its CT number, which is statistically lower than its fluid condition. This phenomenon shows no significant difference according to the reconstruction thickness. H2O: tap water, fNaCl: iced (frozen, with gas) saline, NaCl: saline, fH2O: ice cubes (frozen, without gas). (b) Comparing CT value between ice with and without gas. fNaCl shows lower CT value than fH2O. This phenomenon shows no significant difference according to the reconstruction thickness. fNaCl: iced (frozen, with gas) saline fH2O: ice cubes (frozen, without gas).
H. Hyodoh et al. / Journal of Forensic Radiology and Imaging 3 (2015) 210–213
the mucous membrane of the gastric wall [17]. In addition on PMCT, maintained lung aeration [4], presence of urinary blood [18], and discoloration of joint fluid of the knees and distension of the lung [19] were reported, but not hypodensity of the tissue [7] in the cadaver. In our result, the decreased CT density was not correlated to the cause of death, but enhanced by frozen tissue condition. The partial volume effect might be a cause of the decreasing CT density when the tissue was frozen on CT. There were some limitations in this study. First, this was an ex vivo experimental evaluation, so different circumstances may have effects in the cadaver's PMCT, such as the ratio of fat/air contained in its voxel. Second, the pixel size was minimized according to the CT performance in this study. However, the low density in the cadaver might make it difficult to distinguish an iced tissue from intra-body gas if small particles are contained in the voxel on PMCT. Third, the CT density might show as a similar value in the case of contained fat, due to the partial volume effect. When interpreting postmortem images, background information is required to make a precise diagnosis. Fourth, the accuracy of CT density is the same as the clinical settings, so that the measurement error might exert an effect on the image. In addition, the potential discrepancies of HU measurements as those may be scanner, monitor and parameter dependent. This might affect the discrepancy compared to the theoretical result.
5. Conclusion We experimentally evaluate the freezing (iced) effect and confirmed that the CT density is decreased to around 80 HU. In cases where low density is found when a cadaver is undergoing a CT examination at low temperature, including the freezing effect as a new differential diagnosis could result in more accurate PMCT interpretation.
Acknowledgment We thank Prof. Dr. Myles O’Brien (Mie Prefectual College of Nursy, Tsu, Mie, Japan) for assistance with English Language.
References [1] L. Patriquin, A. Kassarjian, M. Barish, L. Casserley, M. O’Brien, C. Andry, et al., Postmortem whole-body magnetic resonance imaging as an adjunct to autopsy: preliminary clinical experience, J. Magn. Reson. Imaging 13 (2001) 277–287.
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