Email : email@example.com
My major research interest falls in the area of advanced image acquisition and processing
techniques for Magnetic Resonance Imaging (MRI) and Spectroscopy in Medicine. As my
second interest, I conduct research in Wireless Communication Channel Modeling. These
• Magnetic Resonance Imaging
- Clinical Application of Single-Voxel and Multi-Voxel MR Spectroscopy in Brain, Spine and
Magnetic resonance spectroscopy (MRS) allows the non-invasive measurement of selected
biological compounds in vivo. Feasibility was first demonstrated in humans in the mid-
1980s. Since that time, much experience has been accumulated with the use of MRS in both
research and clinical applications. Nearly all MRI scanners have the capability to perform
MRS, and MRS techniques still continue to improve, even after two decades of
development. MRS has been applied to the study of all major pathologies, particularly in
the brain, but has also found application in other organ systems as well, like musculoskeletal
and spine. In spite of this considerable research effort and the unique biochemical
information provided, only limited integration of MRS into clinical practice has occurred to
date. Here at the Tehran University of Medical Sciences, I have established close
collaborations among technical research as well as clinics to explore potentials of MRS as
an emerging technique into clinics, and in a few selected problems like quantification of softtissue
tumors (e.g. ewing- sarcoma and osteo-sarcoma), brain tumors and spinal injuries (e.g.
- MRI-Guided Attenuation and Scatter Correction Positron Emission Tomography (PET) in Brain
Reliable attenuation correction methods for quantitative 3D PET require accurate
delineation of both the organ contour and spatial distribution of attenuation coefficients. To
this end, it is necessary to carefully segment body organs into three different categories of
soft tissue (e.g. muscle and fat), hard tissue (e.g. bone) and air (e.g. lung cavity).
Conventional MRI (cMRI) techniques can easily segment out the soft-tissue, while they
usually confuse bone and air since they both do not enough visible signals in cMRI.
Therefore, advanced MR imaging techniques like UTE-based methods are required to
distinguish bone from air. Here at Tehran University of Medical Sciences, I have established
strong collaborations with our nuclear medicine center to conduct mutual research, starting
with PET/MR imaging in brain and pelvis.
- Ultra-Short Echo-Time (UTE) Imaging for Quantification of Bone Water in Cortical Bone:
A significant portion of the bones mechanical competence is attributed to the composition
and micro-architecture of cortical bone. Although the age-related thinning of the cortex is
partially offset by periosteal expansion, this process is accompanied by other remodeling
changes that adversely affect bone quality.
Key among these is an age-related increase in cortical porosity that is exacerbated in
osteoporosis. Although the mechanism for this process is poorly understood, there is
evidence from histomorphometry that in the femoral neck of hip fracture patients, Haversian
canals are expanded as a result of formation of “composite” osteonal systems in which a
single canal is surrounded by multiple packets of osteonal bone. In this study, we proposed
a new 3D hybrid-radial variable-TE sequence with half-pulse selective excitation to image
the micro-structure of the cortical bone and to accurately quantify the bone water and bone
porosity, by inference, in cortical bone, specifically in the tibial shaft. The experiment was
designed at 123MHz on a TIM Trio MR system (Siemens Medical Solutions). In this
project, I developed all imaging pulse sequences, reconstruction codes and analysis
techniques to precisely capture and to analyze the acquired bone water signal. I managed a
clinical study to analyze sixty five subjects in different age ranges in order to establish a baseline
for the new introduced metric of bone water concentration.
- Motion Correction for High-Resolution Trabecular Bone Imaging Employing Projection Navigators:
High-resolution magnetic resonance imaging (micro-MRI) captures structural details of
trabecular bone (TB) that are reflective of metabolic bone disease and treatment. Necessary
resolutions to resolve TB are in the order of the structure’s thickness: ∼100-200μm.
Three-dimensional imaging of TB is hindered by involuntary rigid body motion as it causes
significant blurring of the TB structure. Motion correction techniques that are developed to
correct for different types of motion (translation, rotation, etc), and to provide high precision
on the order of a half voxel dimension, still suffer from: 1) not enough signal-to-noise ratio
(SNR) for high-precision detection, and 2) not enough degrees of freedom for both
translation and rotation detection. In this study, I proposed a novel motion
detection/correction technique based on acquiring high SNR low-resolution full images as
navigators using advanced SNR enhancement techniques. I also developed all required
pulse sequences as well as reconstruction codes in MATLAB in order to implement it on a
Siemens 1.5T MAGNETOM Sonata scanner.
- Compressed Sensing MRI:
MRI requires a relatively long scan time compared to other biomedical imaging modalities,
which makes it also expensive. MRI data are collected in the spatial-frequency domain,
denoted by k-space. MRI data acquisition can be accelerated by undersampling k -space
from the Nyquist rate. As a new project in the field, I have introduced high performance
compressed sensing algorithms to accelerate the current time-consuming micro-MRI of
trabecular as well as whole body MR Angiography (MRA).
- High Field (7T) In vivo Phosphorus (31P) Imaging of Cortical Bone:
Phosphorus concentration of bone plays an important role in the maintenance of bone
strength in disorders such as osteomalacia which is characterized by hypomineralization of
bone. 31P MRI potentially provides a noninvasive method to evaluate the degree of bone
mineralization, however it is difficult to obtain sufficient SNR at desirable resolutions due
to the extremely short T2* (∼220μsec) and long T1 (∼50sec) of bone phosphorus, as well as
its relatively small gyromagnetic ratio. We estimate that 31P SNR at 7T is intrinsically about
1000 times less than that of muscle water. For this reason, optimization of the imaging
hardware, pulse sequence and post processing is particularly important. In this study, we
constructed small surface coils for use in a 7T whole-body MRI scanner and developed a 3D
radial concentric-cone imaging sequence to image 31P of tibial cortical bone in vivo.
- Large Flip Angle RF Pulse Design with Inverse Scattering Transform
Magnetization transfer (MT) contrast can be used in MRI as an endogenous tissue contrast.
Large flip angle, off-resonance RF pulses are commonly used for MT contrast generation.
Small tip angle approximation and SLR techniques are two robust and efficient methods
in design of low flip angle pulses, however they are not practical in high flip angle (>180)
pulse design. In this study, I investigated the use of inverse scattering transform (IST) as an
alternative strategy for high flip angle pulse design.
• Wireless Channel Modeling
- Space-Time-Frequency Characterization of Wireless Channels:
Wave propagation in two- dimensional and three-dimensional random scattering media,
MIMO multi-carrier wireless channels, narrowband and wideband wireless channel
characterization, straight and non-straight movements of the mobile station (MS), random
movements of MS and/or scatterers, fading statistics of Rayleigh channels, modeling and
evaluation of MIMO relay channels (Ph.D. work and individual works to advise master
- Capacity Evaluation of Wireless Channels:
Information theoretic approaches to antenna design in MIMO systems, capacity analysis of
MIMO systems employing realistic channel correlation models (individual works to advise
• Space-Time Coding Techniques
- Space-Time Coding Ambiguities:
Identification of space-time coding ambiguities in joint adaptive channel estimation and
• Image Processing
Theoretical methods in inverse imaging and 3D image reconstruction