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Connor Elkhill

Biomedicial Physics, '17


Implementation of novel MR-based attenuation correction in PET/MR pelvic scans

Mentor: Ciprian Catana, MD, PhD (MGH)

The use of multiple imaging modalities has become a vital tool in clinical oncology for diagnosing and monitoring the spread of disease. Currently, the most widely implemented systems are combined PET/CT scanners, which sequentially acquire PET and CT data, reducing scanning and analysis time. In the past few years PET/MRI has emerged as a potentially superior modality, as MR provides images with enhanced contrast and eliminates the problem of ionizing radiation from the CT scan. The clinical adoption of these machines has been slower than that of PET/CT a decade ago because there are still many challenges that need to be overcome, one of them being attenuation correction. The creation of accurate attenuation maps is essential in the use of PET systems. These maps are used to correct for the body’s tissues attenuating the PET signal as it travels to the detectors outside the subject. In a PET/CT scanner, the information is provided by the CT scan. However, in a PET/MRI device, the MRI does not provide similar information by default, so an alternate method must be devised. Proper attenuation correction means more accurate quantification in PET images. Clinically, absolute quantification would allow for intra-scan comparisons and monitoring of tumors over long periods of time. The quantitative PET data together with the simultaneously acquired MRI information can provide tumor metabolic information coupled with excellent surrounding anatomical detail. With proper attenuation correction, this goal is more achievable. My research involves implementing and testing new methods to tackle attenuation correction in the pelvis. These methods create a pseudo-CT image that takes into account the large amount of bone tissue in the pelvis that causes most of the problems when performing attenuation correction. The goal is to create a feasible way to do attenuation correction, which would allow physicians to obtain quantitative PET data.

Fluorodeoxyglucose (FDG) is a common radiotracer used in Positron Emission Tomography (PET). These PET images can be fused with MR images and even acquired at the same time in a PET/MR device. Proper attenuation correction for the attenuation of the body’s tissues is important for proper quantification and visualization of the PET image. In addition, MRI images provide excellent contrast, allowing many different tissues to be visualized. Source: