Lea Siegenthaler

The influence of body temperature on image contrast in post mortem MRI

OBJECTIVE To assess the temperature dependency of tissue contrast on post mortem magnetic resonance (PMMR) images both objectively and subjectively; and to visually demonstrate the changes of image contrast at various temperatures. MATERIALS AND METHODS The study was approved by the responsible justice department and the ethics committee. The contrast of water, fat, and muscle was measured using regions of interest (ROI) in the orbit of 41 human corpses to assess how body temperature (range 2.1-39.8 °C) relates to image contrast of T1-weighted (T1W) and T2-weighted (T2W) sequences on PMMR. Regressions were calculated using the method of least squares. Three readers judged visible changes of image contrast subjectively by consensus. RESULTS There was a positive relationship between temperature and contrast on T1-weighted (T1W) images and between temperature and the contrast of fat/muscle on T2-weighted (T2W) images. There was a negative relationship between temperature and the contrast of water/fat and water/muscle on T2W images. Subjectively, the influence of temperature became visible below 20 °C on T2W images, and below 10 °C on T1W images. CONCLUSION Image contrast on PMMR depends on the temperature of a corpse. Radiologists involved in post mortem imaging must be aware of temperature-related changes in MR image contrast. To preserve technical quality, scanning corpses below 10 °C should be avoided.

Reduction of background in optoacoustic image sequences obtained under tissue deformation.

For real-time optoacoustic imaging of the human body, a linear array transducer and reflection mode optical irradiation is preferably used. Experimental outcomes however revealed that such a setup results in significant image background, which prevents imaging structures at the ultimate depth limited only by the optical attenuation of the irradiating light and the signal noise level. Various sources of image background, such as bulk tissue absorption, reconstruction artifacts, and backscattered ultrasound, could be identified. To overcome these limitations, we developed a novel method that results in significantly reduced background and increased imaging depth. For this purpose, we acquire, in parallel, a series of optoacoustic and echo-ultrasound images while the tissue sample is gradually deformed by an externally applied force. Optoacoustic signals and background signals are differently affected by the deformation and can thus be distinguished by image processing. This method takes advantage of a combined optoacoustic/echo-ultrasound device and has a strong potential for improving real-time optoacoustic imaging of deep tissue structures.

Sex determination from os sacrum by postmortem CT

Sex determination in forensic practice is performed mostly on sexually dimorphic bones, including pelvic bones such as the os sacrum. Postmortem CT scan provides an easy and fast method for depicting and measuring bone structures prior to elaborate autopsy preparations. To develop a simple and objective method for sex determination in postmortem CT, metric data were evaluated from CT images of the pelvic-associated os sacrum of 95 corpses (49 men and 46 women) from the Canton of Bern, Switzerland. Discriminant function analysis of the data showed that the best accuracy in determining sex was 76.8% and 78.9% with two different observers. It is concluded that measuring the os sacrumin postmortem CT for sex determination has moderate accuracy and should only be applied in combination with other methods.

Reduction of background in optoacoustic image sequences obtained under tissue deformation

For real-time optoacoustic imaging of the human body, a linear array transducer and reflection mode optical irradiation is preferably used. Experimental outcomes however revealed that such a setup results in significant image background, which prevents imaging structures at the ultimate depth limited only by optical attenuation and the signal noise level. Various sources of image background such as bulk tissue absorption, reconstruction artifacts, and backscattered ultrasound could be identified. We therefore developed a novel method which results in significantly reduced background and increased imaging depth. For this purpose, we acquire in parallel a series of optoacoustic and echo-ultrasound images while the tissue sample is gradually deformed by an externally applied force. Optoacoustic signals and background signals are differently affected by the deformation and can thus be distinguished by image processing. This method takes advantage of a combined optoacoustic/echo-ultrasound device and has a strong potential for improving real-time optoacoustic imaging of deep tissue structures.