Optimising dynamic imaging of brain tumours with the world’s first clinical simultaneous SPECT/MRI
Multimodal diagnostic imaging has gained interest over the years, due to its distinct advantages over single imaging modalities. Hybrid SPECT/CT, PET/CT and, more recently, PET/MRI systems have provided clinicians with high-resolution morphological images in combination with images depicting functional or molecular processes. In contrast with PET/MRI development, SPECT/MRI systems are not yet available as commercial clinical systems. Under EU funding a compact, stationary, MRI-compatible SPECT (single photon emission computed tomography) system has been developed. This will be installed at UCL/UCH as the world’s first clinical simultaneous SPECT/MRI system. This exciting development provides considerable scope for innovative research aimed at improving image quality, extracting quantitative information and applying the new hybrid technology for evaluation of brain tumour patients undergoing therapy. The fundamental unit of the INSERT system is a 5×10 cm gamma camera with high intrinsic resolution. Twenty of these detectors are arranged in a partial ring. The scanner is equipped with a novel type of collimator (multi-mini-slit-slat), which was designed for high sensitivity rather than high resolution. The INSERT system contains a custom made RF coil in order to achieve the necessary MRI image quality, without being disturbed by the SPECT system.
Aims and Objectives: This project will be centred on dynamic imaging with the INSERT system, and will involve tomographic reconstruction, motion correction, partial volume correction and kinetic analysis. Kinetic analysis can be used for estimating physiological or biochemical parameters related to the tracer uptake, such as blood flow, blood volume, volume of distribution, binding potential and metabolic rate. It has been shown that kinetic parameters are superior to static uptake values in various clinical applications. Kinetic analysis requires dynamic data acquisition. Most standard SPECT systems consist of large rotating scintillation cameras, which makes it difficult to perform dynamic studies. The INSERT scanner, on the other hand, is a stationary system, which facilitates dynamic acquisition and kinetic analysis. A limitation associated with dynamic imaging is that the use of short time-frames leads to a high noise-level. One way to address this problem is to use a 4D reconstruction method, taking into account the correlation between the data in consecutive time-frames. Another problem is that the image analysis will be sensitive to the presence of patient motion during the data acquisition. The MRI data can be used to correct for motion. In addition the availability of high resolution anatomical information from MRI allows for the use of partial volume correction, which can substantially improve the images both qualitatively and quantitatively. The successful applicant will work as part of a team that explore the potential of this new hybrid technology in the setting of cancer treatment.