An equation-free introduction to post-mortem MR image contrast and pulse sequence optimization

• Reviews current progress toward optimizing post-mortem MR for forensic application.
• Provides a practical explanation of pulse sequences, relaxation, and tissue contrast.
• Describes how to optimize pulse sequences for users with varying levels of expertise.

Due to the excellent sensitivity of Magnetic Resonance (MR) imaging to subtle differences in soft tissues, MR enables non-invasive anatomical imaging with superior soft tissue contrast relative to X-ray Computed Tomography (CT). However, relative to the X-ray modalities, the utility of MR in the post-mortem setting is currently less well-defined. MR is significantly different from the X-ray modalities, in terms of the underlying principles of image formation, the equipment and expertise necessary to acquire the images, and the appearance of the images themselves. Because MR is sensitive to subtle differences in soft tissues, factors unique to the post-mortem setting, particularly variations in body temperature, tend to have a greater effect on MR imaging relative to the X-ray modalities. Fortunately, MR is inherently flexible and adaptable; there are many types of MR protocols, each with user-controlled parameters that can be adjusted to achieve the best imaging of a specific pathology or anatomic structure, at a given temperature or post-mortem interval (PMI). Optimizing, validating, and standardizing post-mortem MR (PMMR) protocols represents a challenging yet achievable long-term goal. For those interested in developing a better understanding of how to optimize PMMR image quality, this review is intended to provide some guidance, from a technical (but non-mathematical) perspective. A practical explanation of basic pulse sequences and MR relaxation times, and their relationship to tissue contrast, is provided. Strategies for optimizing PMMR for forensic imaging applications, suitable for users with varying levels of expertise, are discussed in the context of current progress in this area.