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Alexander C. Wright, Ph.D.

Research Associate Professor of Radiology
Deputy Director, Laboratory for Structural NMR Imaging

Area: Development of techniques toward cellular MR microscopy of tissues; design of cryogenically cooled RF coils for increased SNR.

Department of Radiology
University of Pennsylvania Health System
1 Founders Building
3400 Spruce Street
Philadelphia, PA 19104
P : (215) 349-5295
F : (215) 662-7263

Dr. Wright’s research involves collaborative, application-specific development of micro-MRI and micro-CT instrumentation and image acquisition strategies that enable qualitative and quantitative analyses of the structure of biological tissues at a near-cellular scale.

RF Coil for In Vivo Micro-MRI of Human Ankle Bone:

In order to provide high SNR for image-based assessment of trabecular bone morphology in the human distal tibia, thereby facilitating quantitative analyses of osteoporotic fracture risk, a novel transmit-receive radio-frequency (RF) coil for use in a whole-body 7T MRI scanner was designed and constructed in collaboration with a commercial manufacturer.

a) 7T RF coil for micro-MRI of the distal tibia (1). (b) Volume rendered micro-MRI data (artificially colored and cropped) of trabecular bone in the distal tibia of a human volunteer, acquired at 7T using the RF coil in (a).

Gradient Coil for q-Space Micro-MRI of Mouse Spinal Cord:

The method of q-space imaging (diffusion diffraction) can be used to non-invasively map axon diameters in the spinal cord as a means to characterize injury and recovery. It does not require individual axons to be resolved in the image, yet it does require very high amplitude, short duration gradient pulses. For this purpose, a high-strength, 50 T/m z-axis gradient coil was constructed and interfaced to a commercial 9.4T MR micro-imaging system, enabling 4D (3 spatial, 1 diffusional) q-space imaging for the ex vivo characterization of spinal cord injury in a mouse model.

(a) Micro-Z gradient coil for high-resolution q-space imaging of mouse spinal cord (2). (b) Q-space map of mouse spinal cord, showing the FWHM of the displacement profile within each voxel.

Image-Based Biomechanical Modeling of Human Intervertebral Disc:

Micro-MRI (including micro-DTI and relaxometry) and MR elastography methods applied to the intervertebral disc can inform the development of accurate biomechanical models to predict degeneration and therapeutic outcomes, and furthermore have in vivo diagnostic potential. In collaboration with researchers in Orthopaedic Surgery, these MR methods are under development to visualize and quantify tissue microstructure in the annulus fibrosus, nucleus pulposus, and cartilaginous endplates of the disc.

Tissue Micro-Morphology and Gene Expression by Micro-CT:

Under development as well, and in collaboration with numerous research groups at Penn and abroad, are micro-CT contrast agents and techniques for the evaluation of gene expression in both soft-tissue and calcified specimens. For example, the micro-architecture of human cortical bone can be visualized at extremely high resolution (1-10 µm isotropic) using micro-CT.



Volume rendering (1 µm isotropic resolution) of a micro-CT data set from a specimen of human tibial cortical bone, using shape-segmented to allow visualization of the micro-vascular network (orange) as well as individual osteocyte lacunae (blue).
See also the cover of the recent December 2012 issue of the Journal of Bone and Mineral Research.

Low-Noise RF Coils for Micro-MRI:

As a means to reduce electronic noise and improve SNR in SNR-limited applications such as high-resolution micro-MRI, the use of insulated, cryogenically cooled RF coils has been explored. SNR gain factors of 2-3x improvement have been demonstrated in specific applications.

In vivo micro-MRI of a rabbit’s eye, using (a) a room-temperature copper RF coil, and (b) the same coil and image acquisition parameters but with the coil cooled in liquid nitrogen to 77 K. SNR gain was ≥ 2x.