Imaging Applications for Genomic Diagnostics of Brain Tumors
When examining brain tumor tissues, genetic information in tissue samples is a crucial factor in the WHO (World Health Organization) classification. Particularly, the presence or absence of IDH1/IDH2 mutations is a significant factor in gliomas, the most common type of primary brain tumor. Genetic mutations in IDH1 can be identified by directly sampling and analyzing the tumor tissue. However, there are methods to determine these mutations without invasive procedures, such as biopsies or surgeries.
Among these methods, combining MRI (Magnetic Resonance Imaging) with MR spectroscopy (MRS) significantly enhances diagnostic accuracy (Fig. 1).
MRS is a technique that measures the metabolites within tissues such as brain tumors, in addition to the anatomical information provided by MRI. However, only a limited number of hospitals apply MRS in actual clinical settings. Our department of radiology has extensive experience with MRS, especially in diagnosing IDH mutations in brain tumors. We have independently developed a sequence called MEGA-PRESS to detect 2-hydroxyglutarate, which is produced due to IDH mutations, and use a special program for analysis, enabling high-precision diagnosis of IDH mutations (Fig. 2). This allows for predicting IDH mutations before surgery, aiding in the smooth selection of postoperative treatments and patient management.
Imaging Applications for Genomic Diagnostics of Early Dementia
A known genetic cause of early-onset Alzheimer’s disease is the mutation of the APOE gene. Particularly, the APOE-ε4 allele is known to be a risk factor for Alzheimer’s disease. Individuals with this mutation show an increase in a substance called myo-inositol (mIns) in certain areas of the brain even before symptoms appear, compared to healthy individuals.
This mIns can be measured using MRS, and our department of radiology uses MRS to check for elevated mIns levels during the diagnosis of early dementia. Detecting changes in mIns allows for the early diagnosis of Alzheimer’s disease, providing crucial information for selecting and assessing the effectiveness of disease-modifying drugs2 for Alzheimer’s disease, which are expected to receive insurance coverage in the future.