Muhammad Nasir Ullah

All Publications

• Ultra-High Spatial Resolution Clinical Positron Emission Tomography (PET) Systems APPLIED SCIENCES-BASEL Chin, M., Ullah, M., Innes, D., Levin, C. S. 2025; 15 (9)

  View details for DOI 10.3390/app15095207

  View details for Web of Science ID 001486743000001

• PETcoil: first results from a second-generation RF-penetrable TOF-PET brain insert for simultaneous PET/MRI. Physics in medicine and biology Dong, Q., Ullah, M. N., Innes, D. R., Watkins, R. D., Chang, C., Zou, S. J., Groll, A., Sacco, I., Chinn, G., Levin, C. S. 2024

  Abstract

  Simultaneous PET/MRI provides concurrent information about anatomic, functional, and molecular changes in disease. We are developing a second generation MR-compatible RF-penetrable TOF-PET insert. The insert has a smaller scintillation crystal size and ring diameter compared to clinical whole-body PET scanners, resulting in higher spatial resolution and sensitivity. This paper reports the initial system performance of this full-ring PET insert. The global photopeak energy resolution and global coincidence time resolution, 11.74 ± 0.03 % FWHM and 238.1 ± 0.5 ps FWHM, respectively, are preserved as we scaled up the system to a full ring comprising 12,288 LYSO-SiPM channels. Throughout a ten-hour experiment, the system performance remained stable, exhibiting a less than 1% change in all measured parameters. In a resolution phantom study, the system successfully resolved all 2.8 mm diameter rods, achieving an average VPR of 0.28 ± 0.08 without TOF and 0.24 ± 0.07 with TOF applied. Moreover, the implementation of TOF in the Hoffman phantom study also enhanced image quality. Initial MR compatibility studies of the full PET ring were performed with it unpowered as a milestone to focus on looking for material and geometry-related artifacts. During all MR studies, the MR body coil functioned as both the transmit and receive coil, and no observable artifacts were detected. As expected, using the body coil also as the RF receiver, MR image signal-to-noise ratio exhibited degradation (∼30%), so we are developing a high quality receive-only coil that resides inside the PET ring.

  View details for DOI 10.1088/1361-6560/ad7221

  View details for PubMedID 39168156

• Self-normalization for a 1-mm3resolution clinical PET system using deep learning. Physics in medicine and biology Chin, M., Jafaritadi, M., Franco, A. B., Ullah, M. N., Chinn, G., Innes, D. R., Levin, C. S. 2024

  Abstract

  Normalization in positron emission tomography (PET) corrects for non-uniformity of sensitivity across all system lines of response (LOR). Self-normalization is a framework that aims to estimate normalization components from the emission data without a separate scan of a normalization phantom. In this work, we propose for the first time an image-based end-to-end self-normalization framework using conditional generative adversarial networks (cGAN). We evaluated different approaches by exploring each of the following three methodologies. First, we used images that were either unnormalized or corrected for geometric factors, which encompass all time-invariant factors, as input data types. Second, we set the input tensor shape as either a single axial slice (2-D) or three contiguous axial slices (2.5-D). Third, we chose either Pix2Pix or polarized self-attention (PSA) Pix2Pix, which we developed for this work, as a deep learning network. The targets for all approaches were the axial slices of images normalized using the direct normalization method. We performed Monte Carlo simulations of ten voxelized phantoms with the SimSET simulation tool and produced 26,000 pairs of axial image slices for training and testing. The results showed that 2.5-D PSA Pix2Pix trained with geometric-factors-corrected input images achieved the best performance among all the methods we tested. All approaches improved general image quality figures of merit peak signal to noise ratio (PSNR) and structural similarity index (SSIM) from ~15% to ~55%, and 2.5-D PSA Pix2Pix showed the highest PSNR (28.074) and SSIM (0.921). Lesion detectability, measured with region of interest (ROI) PSNR, SSIM, normalized contrast recovery coefficient (NCRC), and contrast-to-noise ratio (CNR), was generally improved for all approaches, and 2.5-D PSA Pix2Pix trained with geometric-factors-corrected input images achieved the highest ROI PSNR (28.920) and SSIM (0.973).

  View details for DOI 10.1088/1361-6560/ad69fb

  View details for PubMedID 39084640

• Advances in Detector Instrumentation for PET. Journal of nuclear medicine : official publication, Society of Nuclear Medicine Gonzalez-Montoro, A., Ullah, M. N., Levin, C. S. 2022; 63 (8): 1138-1144

  Abstract

  During the last 3 decades, PET has become a standard-of-care imaging technique used in the management of cancer and in the characterization of neurologic disorders and cardiovascular disease. It has also emerged as a prominent molecular imaging method to study the basic biologic pathways of disease in rodent models. This review describes the basics of PET detectors, including a detailed description of indirect and direct 511-keV photon detection methods. We will also cover key detector performance parameters and describe detector instrumentation advances during the last decade.

  View details for DOI 10.2967/jnumed.121.262509

  View details for PubMedID 35914819

• Application of Artificial Intelligence in PET Instrumentation. PET clinics Ullah, M. N., Levin, C. S. 2022; 17 (1): 175-182

  Abstract

  Artificial intelligence (AI) has been widely used throughout medical imaging, including PET, for data correction, image reconstruction, and image processing tasks. However, there are number of opportunities for the application of AI in photon detector performance or the data collection process, such as to improve detector spatial resolution, time-of-flight information, or other PET system performance characteristics. This review outlines current topics, research highlights, and future directions of AI in PET instrumentation.

  View details for DOI 10.1016/j.cpet.2021.09.011

  View details for PubMedID 34809865

• Wavelength discrimination (WLD) detector optimization for time-of-flight positron emission tomography with depth of interaction information NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT Ullah, M., Park, J., Pratiwi, E., Kim, G., Yeom, J. 2020; 982

  View details for DOI 10.1016/j.nima.2020.164498

  View details for Web of Science ID 000581805300006

• Wavelength discrimination (WLD) TOF-PET detector with DOI information PHYSICS IN MEDICINE AND BIOLOGY Ullah, M., Pratiwi, E., Park, J., Lee, K., Choi, H., Yeom, J. 2020; 65 (5): 055003

  Abstract

  Depth-of-interaction (DOI) encoding can contribute to improving spatial resolution uniformity and sensitivity in positron-emission-tomography (PET) scanners. In addition, time-of-flight (TOF) PET scanners with DOI encoding have received considerable interest because of their potential for improving the spatial resolution, sensitivity, and image quality of the overall system. In this study, a new DOI detector configuration utilizing scintillators' emission wavelength is proposed, and experimental results on the energy, timing, and DOI performance of the detector are provided. The DOI information from the proposed phoswich-type detector can be acquired at the detector level without complex signal processing by utilizing a single optical filter with customized optical properties. For this, we used either a short pass filter (SPF) or a long pass filter (LPF) that allows light photons of a specific wavelength to pass. The two-layered phoswich detector was configured with two scintillators with different photon-emission spectra. In this study, we used Ce:GAGG (3 mm  ×  3 mm  ×  10 mm) and LYSO:Ce (3 mm  ×  3 mm  ×  10 mm) as the top and bottom layer scintillators, respectively. A digital silicon photomultiplier (dSiPM) was used as the photosensor and for data acquisition. The phoswich detector was placed in the center of two dSiPM pixels, where one of the dSiPM pixels was covered with the optical filter, and the light guide was placed on the other pixel. The detector was tested for energy, timing, and DOI encoding performance. When an SPF was used, the energy resolutions of 16.2% and 11.8% were achieved for the Ce:GAGG (top layer) and LYSO:Ce (bottom layer) respectively without correcting for saturation effect. With a small (3 mm  ×  3 mm  ×  5 mm) LYSO crystal as the reference detector, CRTs (coincidence-resolving times) of 338 ps and 244 ps were recorded for the top and bottom layers respectively. The detector configuration also provides an excellent DOI-separation figure-of-merit (FoM) value of 1.9. In the case of LPF, the energy resolutions of 12.0% and 12.9% were achieved for the Ce:GAGG (top layer) and LYSO:Ce (bottom layer), respectively. CRTs (coincidence resolving times) of 314 ps and 263 ps were recorded for the top and bottom layers, respectively. The DOI-separation FoM value of 1.5 was achieved in this setup. Results show that the proposed method can provide excellent discrete DOI positioning accuracy without compromising the timing performance of the detector.

  View details for DOI 10.1088/1361-6560/ab6579

  View details for Web of Science ID 000519034300001

  View details for PubMedID 31874462

• Collimators for Gamma Dual Energy CT Arch-Detector: A Simulation Study JOURNAL OF THE KOREAN PHYSICAL SOCIETY Pratiwi, E., Bae, S., Lee, H., Ullah, M., Lee, B., Lee, K., Yeom, J. 2020; 76 (1): 79–85

  View details for DOI 10.3938/jkps.76.79

  View details for Web of Science ID 000511872400013

• A new positron-gamma discriminating phoswich detector based on wavelength discrimination (WLD) NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT Ullah, M., Park, C., Pratiwi, E., Kim, C., Choi, H., Yeom, J. 2019; 946

  View details for DOI 10.1016/j.nima.2019.162631

  View details for Web of Science ID 000503433900003

• Investigation of Optical Properties of Ceramic Ce:GAGG by High Temperature Annealing JOURNAL OF THE KOREAN PHYSICAL SOCIETY Park, C., Ullah, M., Kim, C., Cho, S., Yeom, J. 2019; 75 (12): 962–67

  View details for DOI 10.3938/jkps.75.962

  View details for Web of Science ID 000508392300006

• Studies on sub-millimeter LYSO:Ce, Ce:GAGG, and a new Ce:GFAG block detector for PET using digital silicon photomultiplier NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT Ullah, M., Pratiwi, E., Park, J., Yamamoto, S., Kamada, K., Yoshikawa, A., Yeom, J. 2018; 911: 115–22

  View details for DOI 10.1016/j.nima.2018.09.029

  View details for Web of Science ID 000450880200017

• Instrumentation for Time-of-Flight Positron Emission Tomography NUCLEAR MEDICINE AND MOLECULAR IMAGING Ullah, M., Pratiwi, E., Cheon, J., Choi, H., Yeom, J. 2016; 50 (2): 112–22

  Abstract

  Positron emission tomography (PET) is a molecular imaging modality that provides information at the molecular level. This system is composed of radiation detectors to detect incoming coincident annihilation gamma photons emitted from the radiopharmaceutical injected into a patient's body and uses these data to reconstruct images. A major trend in PET instrumentation is the development of time-of-flight positron emission tomography (ToF-PET). In ToF-PET, the time information (the instant the radiation is detected) is incorporated for image reconstruction. Therefore, precise and accurate timing recording is crucial in ToF-PET. ToF-PET leads to better localization of the annihilation event and thus results in overall improvement in the signal-to-noise ratio (SNR) of the reconstructed image. Several factors affect the timing performance of ToF-PET. In this article, the background, early research and recent advances in ToF-PET instrumentation are presented. Emphasis is placed on the various types of scintillators, photodetectors and electronic circuitry for use in ToF-PET, and their impact on timing resolution is discussed.

  View details for DOI 10.1007/s13139-016-0401-5

  View details for Web of Science ID 000386256200004

  View details for PubMedID 27275359

  View details for PubMedCentralID PMC4870467