L. Tugan Muftuler, PhD
Department of Neurosurgery
Froedtert West Clinics
9200 W. Wisconsin Avenue
Milwaukee, WI 53226
RESEARCH AREA/Interest: To develop novel hardware and imaging techniques to achieve higher sensitivity and specificity to the pathophysiology of various diseases in diagnostic imaging
Neuroimaging: High resolution functional MRI and Diffusion Tensor Imaging. Cortical shape and morphology analysis.
Imaging techniques to study spinal disc degeneration.
Novel MRI RF coil (probe) design and novel MR Imaging pulse sequences and protocols.
Magnetic Resonance Electrical Impedance Tomography.
Education and Research
Orta Dogu Technical University, Ankara, Turkey
BSc in Electrical Electronics Engineering (Specialized on RF and Microwave eng.). 1987.
M.Sc. in Electrical Electronics Engineering. 1990. High speed, two-frame video data acquisition system for digital subtraction angiography.
Ph.D. in Electrical Electronics Engineering with Y. Ziya Ider. September 1990 – August 1996 Measurement of Magnetic Field Generated by Nonuniform AC Current Density Using Magnetic Resonance "Design and construction of a research MRI system"
University of California at Irvine, Irvine, CA
Postdoctoral fellow. 1998
The primary research goal of my lab is to address engineering challenges in diagnostic imaging to achieve higher sensitivity and specificity to the pathophysiology of various diseases. In order to accomplish these goals, we have developed novel hardware and imaging protocols (pulse sequences) for Magnetic Resonance Imaging (MRI) systems and utilized these new technologies in various neuroimaging, musculoskeletal imaging and cancer imaging research studies.
Our objective is to establish a strong research program in MRI technology and build productive collaborations with researchers from diverse backgrounds, which is essential to address increasingly complex issues in the field of healthcare.
MR based Electrical Impedance Tomography (MREIT):
This is a new imaging technique that provides image contrast based on electrical properties of tissues. We successfully applied this technique to study conductivity changes in animal models of breast cancer.
Figure 1. Structural and MREIT images of two animals bearing R3230AC tumor model of breast cancer. Top row is T2 weighted MRI images and bottom row I the corresponding conductivity images. Red circles indicate the tumor area.
Tissue conductivity becomes a critical factor in the efficiency of RF coils as the MRI operating frequency increases. Therefore, this technique can also be an important tool in developing improved radio-frequency coil designs and could aid in optimized B1 shimming for ultra-high field MRI (7T and higher).
Novel Radio Frequency (RF) coil developments for MRI:
We have developed a new inverse-solution approach to design RF coils optimized for parallel imaging techniques in MRI. Parallel imaging improves the speed of image acquisition. However, it introduces spatially varying degradation in signal to noise ratio (SNR) in images when conventional RF coils are used. In order to address this problem, we derived an inverse problem in which SNR was formulated as a function of coil geometry. This expression is calculated by a Least Squares approach to find the RF coil geometry that maximized the SNR of images. We hold a patent for this approach (Patent no: 7362101) and received the 1st place award in Engineering Category in the 2006 scientific meeting of the International Society of Magnetic Resonance in Medicine (ISMRM) (abstract # 26).
Figure 2. (a) One element of the phased array coil optimized for brain imaging at 1.5T MRI. (b) and (c) are the transverse component of the magnetic flux density in axial and sagittal planes, respectively. (d) shows 1/g factor and (e) and (f) are the full and SENSE accelerated SNR, respectively. The actual coil is shown on the right.
We have also developed various new RF coil designs to achieve better sensitivity for multinuclear MRI. One of those RF coils can be tuned automatically inside the MRI using LabVIEW to achieve the best performance for variations in the loads (objects placed in the coil for imaging). We also developed a PIN diode controlled multinuclear RF coil that improved the SNR by more than two-fold compared to conventional coil designs. These RF coils are essential to study anatomy and metabolism simultaneously. For instance, changes in sodium concentration were implicated in tumors. Similarly, localized sodium deficits were reported in the brain in several cognitive disorders. Thus, one can obtain information about the disease metabolism from the sodium images while hydrogen images provide high-resolution structural information.
Figure 3. Multi-nuclear phased array receive coil inserted into a quad-port fed dual-tuned birdcage transmit coil along with associated electronics.
High Resolution imaging studies of neuroanatomy and function:
Studies of Aging and Dementia:
Investigating subtle changes in tissue structure and metabolism is critical to diagnose diseases at early stages. Therefore, we have studied techniques to improve image resolution and contrast in various neuroimaging studies. For instance, we have recently obtained a very high resolution Diffusion Tensor Images (DTI) of the perforant path in the hippocampus, a very thin and curved axonal fiber tract. Apart from the small size, it resides in a region that is prone to severe distortions and signal loss due to variations in tissue magnetic susceptibility. This fiber tract is implicated in early stages of Alzheimer’s disease.
Figure 4. Data form two subjects, S1 and S2. (a) and (b) show the coronal slice and the anatomical location of the perforant path. (c) shows the strength of diffusion signal perpendicular to the surface of entorhinal cortex. (d) illustrates diffusion signal strength perpendicular to the entorhinal cortex inside the section shown in (b).
Studies of brain development:
We have studied age-associated changes in the cortex, subcortical structures and brain white matter tracts using high resolution T1 weighted images and Diffusion Tensor Images (DTI). The results revealed maps of brain development in preadolescent ages at very high spatial and temporal detail.
Figure 5. Inflated brain surfaces with statistically significant reduction in cortical thickness with age shown with blue overlay (p<0.05, FDR corrected). Upper row is the lateral and medial surfaces of the left hemisphere and lower row is the right hemisphere. Each column shows changes in cortical thickness during the specified age range. The color bar indicates t-scores.
Figure 6. Development of subcortical structures during preadolescent ages. Colors represent F-scores. Caudate, thalamus and hippocampus are shown inside the brain.
Figure 7. Age-associated changes in brain white matter fibers. Significant increase in FA (left panel, red colors) and decrease in MD was shown in Corticospinal tracts. Similar changes were seen in most major fiber tracts in the brain during preadolescent ages.
Multi-parametric MR Imaging of Spinal Disc Degeneration:
We have recently initiated a new research project to study intervertebral disc degeneration using perfusion MRI, DTI, Ultra-short TE and T1rho imaging techniques that utilizes the multi-nuclear RF coils and imaging protocols that we developed. The goal is to explore the pathophysiology of spinal disc degeneration and the mechanisms that lead to this ailment. Our preliminary findings show that the blood perfusion deficiencies in disc endplates are closely associated with degeneration.
Figure 8. T1 weighted sagittal images and Dynamic contrast enhanced MRI (DCEMRI) in the disc endplates.