Clinical Application of Synthetic MRI on Patients with Malignant Gliomas
Patients with malignant gliomas are treated with surgery, chemo- and radiotherapy and then followed with MRI-examinations to detect early signs of tumour recurrence. Almost 25% of patients react to the treatment with oedema and contrast-enhancement in the affected area of the brain, and this image is difficult to distinguish from tumour recurrence. Since the image is non-specific, radiologists in these cases look to more quantitative methods such as MR Spectroscopy and PET-CT, but there are still cases where it is unclear if the patient should be treated with further surgery or just followed with further imaging. Synthetic MRI is a quantitative MR-method that enables quantitative measurement of the tissue. If it is possible to find tumour specific quantitative values, it might be possible to distinguish tumour from treatment effects and thereby improving the diagnostic arsenal in these difficult cases.
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- Project Description:
Gliomas are diffuse, infiltrative tumours derived from the gliacells in the brain. Diagnostically it can be a problem to differentiate between tumour, tumour oedema and, after radiation therapy, the effect of radiation on brain tissue. Patients with malignant gliomas go through extensive magnetic resonans imaging (MRI) examinations before and after surgery, and especially when there is a suspected recurrence of the tumour, which can be difficult to distinguish from radiation necrosis. MRI with contrast is the standard exam for tumours and in addition MR Spectroscopy and PET can be used to improve the diagnostic accuracy. There are, however, still cases where it is unclear whether the patient has a tumour recurrence or a reaction after radiation, and extensive research is carried out in this field to find markers to distinguish between the different states.
A quantitative MR-method ('Synthetic MRI', SyMRI/QMR) has been developed at Centre for Medical Image Science and Visualization (CMIV). Synthetic Magnetic Resonance Imaging is based on a single MR quantification scan to retrieve the absolute values of the longitudinal T1 relaxation (R1), the transverse T2 relaxation (R2), the proton density (PD) and the inhomogeneity of the radio-frequent B1 field. Based on these values the pixel intensity is calculated as a function of the desired MR scanner settings, thereby synthesizing conventional MR images with a free choice of echo time (TE), repetition time (TR) and inversion delay (TI). Based on these parametres it is then possible to postsynthesize images which are T1-, T2- and PD-weighted. The scan time for this new sequence is apprx 6 minutes.
Since SyMRI is quantitative, it enables the radiologist to measure the relaxation of the brain tissue and the pathology, making it possible to acquire tissue segmentation in a fast and simple manner. The method also allows for a quick way to measure volume to evaluate e.g. atrophy, tumour volume and size of the ventricles.
Quantitative measurements and volume calculation can be of importance when analyzing brain tumours, but are typically not available in conventional MR imaging in the daily clinical routine today. Synthetic MRI makes it possible to measure tissue specific relaxation and volume.
60 patients scheduled for surgery/biopsy at the neurosurgery department will be asked to participate. The synthetic MR sequence will be added to the clinical MR-examination before and after surgery and at follow-up during the first year after diagnosis. Quantitative analysis (T1, T2 and Pd relaxation) will be performed for characterization of tumours, measurement of contrast enhancement, automatically calculated tumour volume and degree of tumour infiltration in surrounding tissue. Synthetic images will be compared to conventional images and quantitative measurements will be correlated to histopathological grading of the tumours
Significance of the project
If it is possible to find a pattern of recognition, synthetic MRI might be used as a form of virtual biopsy. If quantitative measurements can differentiate between tumour, tumour oedema and radiation effects it would be of immense value for neurosurgeons and neurooncologists in planning the treatment of patients with gliomas. In addition, it would be a significant advantage also for neuroradiologists for the evaluation of these difficult cases, and of great benefit for patients who would get more accurate treatment.