Applications
The Center for Basic MR Research will run routine MR spectroscopy or imaging experiments on an hourly fee basis. Faculty members of the facility are available to discuss feasibility of a given protocol.
Standard applications of the lab include anatomic, T1, T2, diffusion, and perfusion studies. In addition, global and localized spectroscopy experiments are available for either proton or multinuclear applications. Cultured tissue, excised organ, and in vivo model systems are utilized in the following ongoing studies:
Cultured Tissue
Small (approximately 2 mm) cartilage samples can be imaged with isotropic 50 micron resolution. In the images on the left, a 3D data set is obtained of a cartilage sample; above left is the proton density image demonstrating homogeneous tissue with small blood vessels. Above right is a T1 weighted 3D image demonstrating striking T1 variations across the sample. Bottom left is one 2D section from the 3D data set, demonstrating good correspondence with histology (bottom right).
Isolated Organs
Isolated organs can be imaged in 3D to demonstrate the internal anatomic structures which are difficult to view with 2D histologic slides; on the left is an isolated mouse heart; in the middle is a mouse knee; on the right is an isolated kidney.
Fast Localization
For in vivo imaging of animals, it is desirable to quickly localize the imaging to the area of interest. For this purpose, a "tripilot" scan is used to obtain images in 3 orthogonal directions within one minute. The dark lines in the images below demonstrate where the orthogonal section images have been taken.
In Vivo Imagine
Anatomic in vivo imaging is routine in the head, thorax, and abdomen. Below are images of mouse brain, heart, and kidney.
RARE Sequences
Images can be obtained faster by using a "RARE" sequence, that is obtaining phase encode information during different echoes of a multi-echo sequence, as seen on the right.
3D RARE Sequences
RARE sequences can also be run in 3D; to the left is a 3D data set from a rat head taken with a surface coil; to the right is one section from the data set.
Echo Planar Imaging
Another mode of data acquisition is Echo Planar Imaging, or EPI. The image to the right, of a rat brain, was taken with EPI on the 4.7 Tesla system with a surface coil.
Angiography
Angiographic images can also be obtained with flow compensated gradient echo imaging. On the right is a 3 dimensional image of the vessels in a rat head.
Calculated Parameter Images
In some circumstances, calculated parameter images are desired. In the example shown below, a T1 calculated image of cartilage demonstrates substantial variation in T1 in the presence of Gd(DTPA).
Arterial Spin Labeling
Perfusion weighted imaging via arterial spin labeling is also available. In the example shown below, the first image is an image obtained with saturation of the spins (blood) in the neck region, leading to saturation in the perfused area of the brain. The second image is the "control". A calculated image is shown on the far right.
In Vivo Mouse Cardiac Imaging
Mouse cardiac imaging can be done on a vertical bore 8.5Tesla MRI system or a horizontal bore 4.7Tesla system. Due to the ease of positioning and the lower respiratory motion on the horizontal system, we currently are pursuing most of the cardiac imaging on the 4.7T instrument.
Cardiac images can be obtained in both systole and diastole. The myocardium in each section can be identified and planimetry used to determine the volume of myocardium in each slice. The specific gravity of myocardium was used to convert volume to mass. Ejection fractions can be computed from diastolic and systolic images.
Images can be obtained throughout the cardiac cycle to produce cine loops of cardiac motion.
Direct flow studies can be used to visualize flow within the heart. Fast segmented gradient echo sequences with relatively high flip angles can be used to highlight flow; regurgitant flow results in a signal void.
Localized Spectroscopy
Localized spectroscopy can be done with localized shimming through the "fast-map" shimming program. The spectrum below was obtained from a rat brain (not yet posted).
