Quantitative Relaxometry Metrics for Brain Metastases Compared to Normal Tissues: A Pilot MR Fingerprinting Study

SIMPLE SUMMARY: Brain metastases (BM) are the most common central nervous system tumor in adults. Conventional qualitative magnetic resonance imaging (MRI), including T1- and T2-weighted imaging, assists in the diagnosis, treatment selection, monitoring, and prognostic determination of BM. Quantitative relaxometry (T1 and T2) measurements, besides other quantitative methods like diffusion- and perfusion-weighted MRI, are important for characterization of BMs, as well as elucidation of their underlying tumor tissue patho-physiology. New, rapid relaxometry methods, such as MR Fingerprinting (MRF), can provide tumor patho-physiology information within a single MRI acquisition and a clinically feasible timeframe. The purpose of the present pilot study was to estimate T1 and T2 metric values derived simultaneously from a new, rapid MRF technique and assess their ability to characterize BM and normal-appearing brain tissues. Our results showed that T1 (index for free water content) and T2 (index for tissue morphology) mapping may quantitatively characterize BMs. Our initial findings need to be validated in a larger patient cohort. ABSTRACT: The purpose of the present pilot study was to estimate T1 and T2 metric values derived simultaneously from a new, rapid Magnetic Resonance Fingerprinting (MRF) technique, as well as to assess their ability to characterize—brain metastases (BM) and normal-appearing brain tissues. Fourteen patients with BM underwent MRI, including prototype MRF, on a 3T scanner. In total, 108 measurements were analyzed: 42 from solid parts of BM’s (21 each on T1 and T2 maps) and 66 from normal-appearing brain tissue (11 ROIs each on T1 and T2 maps for gray matter [GM], white matter [WM], and cerebrospinal fluid [CSF]). The BM’s mean T1 and T2 values differed significantly from normal-appearing WM (p < 0.05). The mean T1 values from normal-appearing GM, WM, and CSF regions were 1205 ms, 840 ms, and 4233 ms, respectively. The mean T2 values were 108 ms, 78 ms, and 442 ms, respectively. The mean T1 and T2 values for untreated BM (n = 4) were 2035 ms and 168 ms, respectively. For treated BM (n = 17) the T1 and T2 values were 2163 ms and 141 ms, respectively. MRF technique appears to be a promising and rapid quantitative method for the characterization of free water content and tumor morphology in BMs.