Biospec 4.7T MRI
Instrument
The Small Animal Imaging Facility at MD Anderson began in September 2001 with the installation of a 4.7T small animal MRI system. The Biospec USR47/40 (Bruker Biospin MRI, Billerica, MA) is an experimental imaging system built around an actively-shielded 4.7T magnet with a 40-cm bore and cryo-refrigeration that maximizes versatility and flexibility while minimizing the time and cost associated with magnet maintenance.
Four receiver channels enable the use of custom RF arrays that increase imaging efficiency, and two transmit channels support broadband imaging, spectroscopy and spectroscopic imaging. Three interchangeable gradient inserts are set according to the target measurement: the largest, with 26-cm ID bore, provide a maximum gradient amplitude of 100mT/m, while 11.6-cm and 6-cm gradients, optimized for rats and mice, deliver 400 mT/m and 950 mT/m, respectively.
Commercially available RF coils include five linear 1H birdcage-style resonators (20-cm and 7.2-cm ID, actively decoupled, and 35-mm, 25-mm and 15-mm ID transmit/receive) and a dual-tuned 31P/1H actively-decoupled resonator (7.2-cm ID). Custom coils are developed in-house for applications with special requirements.
Applications
MRI is a powerful, non-invasive imaging modality that combines high spatial resolution with exquisite soft-tissue contrast. This instrument is routinely used for longitudinal evaluation of small animal models of cancer through anatomic or functional imaging, including dynamic, contrast-enhanced (DCE-) MRI. Simple anatomic imaging provides an accurate means to visualize disease, often even when the tumor can not be detected by palpation or by other imaging methods. DCE-MRI, when paired with appropriate pharmacokinetic modeling, supplements anatomic data with information about microvascular function.
The efficiency of many imaging protocols can be dramatically increased through the use of a multi-animal imaging system that was developed at MD Anderson to reduce the cost and complexity of imaging in cancer research. This instrument is also commonly used for high-throughput screening, and the evaluation of novel contrast agents, therapeutic agents and imaging methods.
Multi-animal imaging and animal handling systems integrate into the wide bore of the USR47/40 to increase throughput and reduce the cost of imaging in cancer research.
Representative T1-weighted (post-contrast) and T2-weighted images of an orthotopic model of human thyroid cancer. Resolution of 150 µm x 150 µm x 1 mm achieved in approximately four minutes per sequence. Images courtesy of Drs. Stephen Lai and Jeff Myers.
Parametric map overlay against T1-weighted anatomic reference illustrating heterogeneity of microvascular perfusion following radiation therapy. Image courtesy of Drs. David Schwartz, Garth Powis, and Juri Gelovani.
Efficacy of a novel vascular T1-relaxation enhancing contrast agent is demonstrated in this maximum-intensity projection. Images courtesy of Drs. Vikas Kundra and Ananth Annapragada.
