Mouse models have increased our understanding of the pathogenesis of 
medulloblastoma (MB), the most common malignant pediatric brain tumor that often 
forms in the cerebellum. A major goal of ongoing research is to better 
understand the early stages of tumorigenesis and to establish the genetic and 
environmental changes that underlie MB initiation and growth. However, studies 
of MB progression in mouse models are difficult due to the heterogeneity of 
tumor onset times and growth patterns and the lack of clinical symptoms at early 
stages. Magnetic resonance imaging (MRI) is critical for noninvasive, 
longitudinal, three-dimensional (3D) brain tumor imaging in the clinic but is 
limited in resolution and sensitivity for imaging early MBs in mice. In this 
study, high-resolution (100 μm in 2 hours) and high-throughput (150 μm in 15 
minutes) manganese-enhanced MRI (MEMRI) protocols were optimized for early 
detection and monitoring of MBs in a Patched-1 (Ptch1) conditional knockout 
(CKO) model. The high tissue contrast obtained with MEMRI revealed detailed 
cerebellar morphology and enabled detection of MBs over a wide range of stages 
including pretumoral lesions as early as 2 to 3 weeks postnatal with volumes 
close to 0.1 mm(3). Furthermore, longitudinal MEMRI allowed noninvasive 
monitoring of tumors and demonstrated that lesions within and between 
individuals have different tumorigenic potentials. 3D volumetric studies allowed 
quantitative analysis of MB tumor morphology and growth rates in individual 
Ptch1-CKO mice. These results show that MEMRI provides a powerful method for 
early in vivo detection and longitudinal imaging of MB progression in the mouse 
brain.