Bio

Bio


I attended primary and secondary school in Houston, TX, USA. I attended The University of Texas - Austin from 2001-2005 where I double-majored in Electrical Engineering and in Physics. Afterward, I work at Harris Stratex Corporation as a quality control engineer in electronics manufacturing. I entered graduate school in 2007 at The University of Texas, MD Anderson Cancer Center where I earned a Ph.D. in Medical Physics.

I work on the early research and development of biomedical technology. I am primarily interested in the intersection of Physics, Electrical Engineering, and Biomedical Engineering. My objective is to develop new medical and electronic technologies, especially in biomedical imaging, and improve the diagnosis and treatment of disease.

Professional Education


  • Doctor of Philosophy, UnivTexasBiomedicalSciences (2012)
  • Bachelor of Science, University of Texas Austin (2005)

Stanford Advisors


Research & Scholarship

Lab Affiliations


Publications

Journal Articles


  • Order of Magnitude Sensitivity Increase in X-ray Fluorescence Computed Tomography (XFCT) Imaging With an Optimized Spectro-Spatial Detector Configuration: Theory and Simulation IEEE TRANSACTIONS ON MEDICAL IMAGING Ahmad, M., Bazalova, M., Xiang, L., Xing, L. 2014; 33 (5): 1119-1128

    Abstract

    The purpose of this study was to increase the sensitivity of XFCT imaging by optimizing the data acquisition geometry for reduced scatter X-rays. The placement of detectors and detector energy window were chosen to minimize scatter X-rays. We performed both theoretical calculations and Monte Carlo simulations of this optimized detector configuration on a mouse-sized phantom containing various gold concentrations. The sensitivity limits were determined for three different X-ray spectra: a monoenergetic source, a Gaussian source, and a conventional X-ray tube source. Scatter X-rays were minimized using a backscatter detector orientation (scatter direction > 110(°) to the primary X-ray beam). The optimized configuration simultaneously reduced the number of detectors and improved the image signal-to-noise ratio. The sensitivity of the optimized configuration was 10 μg/mL (10 pM) at 2 mGy dose with the mono-energetic source, which is an order of magnitude improvement over the unoptimized configuration (102 pM without the optimization). Similar improvements were seen with the Gaussian spectrum source and conventional X-ray tube source. The optimization improvements were predicted in the theoretical model and also demonstrated in simulations. The sensitivity of XFCT imaging can be enhanced by an order of magnitude with the data acquisition optimization, greatly enhancing the potential of this modality for future use in clinical molecular imaging.

    View details for DOI 10.1109/TMI.2014.2305101

    View details for Web of Science ID 000335379500010

    View details for PubMedID 24770916

  • X-Ray Luminescence and X-Ray Fluorescence Computed Tomography: New Molecular Imaging Modalities IEEE Access Ahmad, M., Pratx, G., Bazalova, M., Xing, L. 2014; 2: 1051 - 1061
  • Evaluation of intrinsic respiratory signal determination methods for 4D CBCT adapted for mice. Medical physics Martin, R., Rubinstein, A., Ahmad, M., Court, L., Pan, T. 2015; 42 (1): 154-?

    Abstract

    4D CT imaging in mice is important in a variety of areas including studies of lung function and tumor motion. A necessary step in 4D imaging is obtaining a respiratory signal, which can be done through an external system or intrinsically through the projection images. A number of methods have been developed that can successfully determine the respiratory signal from cone-beam projection images of humans, however only a few have been utilized in a preclinical setting and most of these rely on step-and-shoot style imaging. The purpose of this work is to assess and make adaptions of several successful methods developed for humans for an image-guided preclinical radiation therapy system.Respiratory signals were determined from the projection images of free-breathing mice scanned on the X-RAD system using four methods: the so-called Amsterdam shroud method, a method based on the phase of the Fourier transform, a pixel intensity method, and a center of mass method. The Amsterdam shroud method was modified so the sharp inspiration peaks associated with anesthetized mouse breathing could be detected. Respiratory signals were used to sort projections into phase bins and 4D images were reconstructed. Error and standard deviation in the assignment of phase bins for the four methods compared to a manual method considered to be ground truth were calculated for a range of region of interest (ROI) sizes. Qualitative comparisons were additionally made between the 4D images obtained using each of the methods and the manual method.4D images were successfully created for all mice with each of the respiratory signal extraction methods. Only minimal qualitative differences were noted between each of the methods and the manual method. The average error (and standard deviation) in phase bin assignment was 0.24 ± 0.08 (0.49 ± 0.11) phase bins for the Fourier transform method, 0.09 ± 0.03 (0.31 ± 0.08) phase bins for the modified Amsterdam shroud method, 0.09 ± 0.02 (0.33 ± 0.07) phase bins for the intensity method, and 0.37 ± 0.10 (0.57 ± 0.08) phase bins for the center of mass method. Little dependence on ROI size was noted for the modified Amsterdam shroud and intensity methods while the Fourier transform and center of mass methods showed a noticeable dependence on the ROI size.The modified Amsterdam shroud, Fourier transform, and intensity respiratory signal methods are sufficiently accurate to be used for 4D imaging on the X-RAD system and show improvement over the existing center of mass method. The intensity and modified Amsterdam shroud methods are recommended due to their high accuracy and low dependence on ROI size.

    View details for DOI 10.1118/1.4903264

    View details for PubMedID 25563256

  • Synergistic Assembly of Heavy Metal Clusters and Luminescent Organic Bridging Ligands in Metal-Organic Frameworks for Highly Efficient X-ray Scintillation JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wang, C., Volotskova, O., Lu, K., Ahmad, M., Sun, C., Xing, L., Lin, W. 2014; 136 (17): 6171-6174

    Abstract

    We have designed two metal-organic frameworks (MOFs) to efficiently convert X-ray to visible-light luminescence. The MOFs are constructed from M6(μ3-O)4(μ3-OH)4(carboxylate)12 (M = Hf or Zr) secondary building units (SBUs) and anthracene-based dicarboxylate bridging ligands. The high atomic number of Zr and Hf in the SBUs serves as effective X-ray antenna by absorbing X-ray photons and converting them to fast electrons through the photoelectric effect. The generated electrons then excite multiple anthracene-based emitters in the MOF through inelastic scattering, leading to efficient generation of detectable photons in the visible spectrum. The MOF materials thus serve as efficient X-ray scintillators via synergistic X-ray absorption by the metal-cluster SBUs and optical emission by the bridging ligands.

    View details for DOI 10.1021/ja500671h

    View details for Web of Science ID 000335369200006

    View details for PubMedID 24730683

  • L-shell x-ray fluorescence computed tomography (XFCT) imaging of Cisplatin PHYSICS IN MEDICINE AND BIOLOGY Bazalova, M., Ahmad, M., Pratx, G., Xing, L. 2014; 59 (1): 219-232

    Abstract

    X-ray fluorescence computed tomography (XFCT) imaging has been focused on the detection of K-shell x-rays. The potential utility of L-shell x-ray XFCT is, however, not well studied. Here we report the first Monte Carlo (MC) simulation of preclinical L-shell XFCT imaging of Cisplatin. We built MC models for both L- and K-shell XFCT with different excitation energies (15 and 30 keV for L-shell and 80 keV for K-shell XFCT). Two small-animal sized imaging phantoms of 2 and 4 cm diameter containing a series of objects of 0.6 to 2.7 mm in diameter at 0.7 to 16 mm depths with 10 to 250 µg mL(-1) concentrations of Pt are used in the study. Transmitted and scattered x-rays were collected with photon-integrating transmission detector and photon-counting detector arc, respectively. Collected data were rearranged into XFCT and transmission CT sinograms for image reconstruction. XFCT images were reconstructed with filtered back-projection and with iterative maximum-likelihood expectation maximization without and with attenuation correction. While K-shell XFCT was capable of providing an accurate measurement of Cisplatin concentration, its sensitivity was 4.4 and 3.0 times lower than that of L-shell XFCT with 15 keV excitation beam for the 2 cm and 4 cm diameter phantom, respectively. With the inclusion of excitation and fluorescence beam attenuation correction, we found that L-shell XFCT was capable of providing fairly accurate information of Cisplatin concentration distribution. With a dose of 29 and 58 mGy, clinically relevant Cisplatin Pt concentrations of 10 µg mg(-1) could be imaged with L-shell XFCT inside a 2 cm and 4 cm diameter object, respectively.

    View details for DOI 10.1088/0031-9155/59/1/219

    View details for Web of Science ID 000328549200011

  • Defining internal target volume using positron emission tomography for radiation therapy planning of moving lung tumors JOURNAL OF APPLIED CLINICAL MEDICAL PHYSICS Riegel, A. C., Bucci, M. K., Mawlawi, O. R., Ahmad, M., Luo, D., Chandler, A., Pan, T. 2014; 15 (1): 279-289
  • Hard X-ray-induced optical luminescence via biomolecule-directed metal clusters CHEMICAL COMMUNICATIONS Osakada, Y., Pratx, G., Sun, C., Sakamoto, M., Ahmad, M., Volotskova, O., Ong, Q., Teranishi, T., Harada, Y., Xing, L., Cui, B. 2014; 50 (27): 3549-3551

    Abstract

    Here, we demonstrate that biomolecule-directed metal clusters are applicable in the study of hard X-ray excited optical luminescence, promising a new direction in the development of novel X-ray-activated imaging probes.

    View details for DOI 10.1039/c3cc48661c

    View details for Web of Science ID 000332483200003

    View details for PubMedID 24463467

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