Optimization of Inversion Time for Postmortem Short-tau Inversion Recovery (STIR) MR Imaging

Abstract

Purpose: Signal intensity and image contrast differ between postmortem magnetic resonance (PMMR) images and images acquired from the living body. We sought to achieve sufficient fat suppression with short-tau inversion recovery (STIR) PMMR imaging by optimizing inversion time (TI).Material and Methods: We subjected 37 deceased adult patients to PMMR imaging at 1.5 tesla 8 to 60 hours after confirmation of death and measured T 1 values of areas of subcutaneous fat with relaxation time maps. Rectal temperature (RT) measured immediately after PMMR ranged from 6 to 31°C. We used Pearson's correlation coefficient to analyze the relationship between T 1 and relaxation time (RT). We compared STIR images from 4 cadavers acquired with a TI commonly used in the living body and another TI calculated from the linear regression of T 1 and RT.Results: T 1 values of subcutaneous fat ranged from 89.4 to 182.2 ms. There was a strong, positive, and significant correlation between T 1 and RT (r = 0.91, P < 0.0001). The regression expression for the relationship was T 1 = 2.6*RT + 90 at a field strength of 1.5T. The subcutaneous fat signal was suppressed more effectively with the optimized TI.Conclusion: The T 1 value of subcutaneous fat in PMMR correlates linearly with body temperature. Using this correlation to determine TI, fat suppression with PMMR STIR imaging can be easily improved.

Hepatic Relaxation Times from Postmortem MR Imaging of Adult Humans

“…Within a small temperature range, the T 1 value depends linearly on the temperature in fat and water. 14 , 15 , 37 – 41 The T 2 value decreases with a declining temperature in fat tissue and aqueous solutions; 37 , 40 , 41 however, the temperature dependence of the T 2 value can be masked by other factors in tissue. 37 …”

“… 9 – 13 The optimization of parameters for PMMR imaging and accurate interpretation of imaging findings require analyses of quantitative data. 14 – 16 T 1 and T 2 values on MR imaging of the human adult liver in vitro and in vivo have been reported. 17 – 22 We surmised that the quantitative data of T 1 and T 2 values of hepatic PMMR imaging of in vivo would help interpret postmortem imaging variation relative to postmortem interval (time elapsed after death), functional failure before death, and/or metabolic abnormality resulting from pharmacologic or toxic substances.…”

Cerebral Relaxation Times from Postmortem MR Imaging of Adults

“…This result will help in the optimization of scan parameters for PMMR imaging, which we are investigating. 18,19 Three major reasons are considered for this difference in MR relaxation times.…”

Optimization of Inversion Time for Postmortem Fluid-attenuated Inversion Recovery (FLAIR) MR Imaging at 1.5T: Temperature-based Suppression of Cerebrospinal Fluid

“…18 However, such a method is applicable only when the CSF is in a normal oxyhemoglobin changes the ADC values of the CSF. 29 Optimization of STIR PMMR imaging using the TI, which is calculated based on RT, allows sufficient suppression of the SI of fat, 22 and we observed effective suppression of the CF signal in FLAIR images by adapting this method. Inadequate suppression of the cadaveric CSF signal even following optimization using this method may indicate the CSF is abnormal, such as in the case of CSF containing blood, findings similar to the abnormal findings in a living body.…”

“…[18][19][20] Suppression of the signal intensity (SI) of fat has been reported with STIR in PMMR imaging when using an optimized TI based on the measured rectal temperature (RT). 22 Therefore, we surmised that the SI of CSF can also be suppressed on postmortem FLAIR images by adjusting the TI according to the T 1 temperature dependence of water. 18,20 In this study, we attempted to achieve sufficient SI suppression of the CSF on cerebral FLAIR PMMR images by optimizing the TI.…”