Publications

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E-prints and Preprints

  1. P. Chandrasekaran, C. Chen, Y. Liu, S. M. Arshad, C. Crabtree, M. Tong, Y. Han, and R. Ahmad, “Accelerated real-time cine and flow under in-magnet staged exercise,” arXiv preprint arXiv:2402.17877, 2024.
  2. X. Lei, P. Schniter, C. Chen, and R. Ahmad, “Surface coil intensity correction for MRI,” arXiv preprint arXiv:2312.00936, 2023.
  3. M. A. Sultan, C. Chen, Y. Liu, and R. Ahmad, “Deep image prior with structured sparsity (DISCUS) for dynamic MRI reconstruction,” arXiv preprint arXiv:2312.00953, 2023.
  4. S. M. Arshad, L. C. Potter, C. Chen, Y. Liu, P. Chandrasekaran, C. Crabtree, Y. Han, and R. Ahmad, “Motion-robust free-running cardiovascular MRI,” arXiv preprint arXiv:2308.02088, 2023.
  5. S. Liu, M. Shafique, P. Schniter, and R. Ahmad, “MRI recovery with self-calibrated denoisers without fully-sampled data,” arXiv preprint arXiv:2304.12890, 2023.
  6. M. Joshi, A. Pruitt, C. Chen, Y. Liu, and R. Ahmad, “Technical report (v1.0)–Pseudo-random Cartesian sampling for dynamic MRI,” arXiv preprint arXiv:2206.03630, 2022.
  7. C. Chen, Y. Liu, P. Schniter, M. Tong, K. Zareba, O. Simonetti, L. Potter, and R. Ahmad, “OCMR (v1.0)–Open-access multi-coil k-space dataset for cardiovascular magnetic resonance imaging,” arXiv preprint arXiv:2008.03410, 2020.

Journal Publications

  1. C. Chen, Y. Liu, O. P. Simonetti, M. Tong, N. Jin, M. Bacher, P. Speier, and R. Ahmad, “Cardiac and respiratory motion extraction for MRI using Pilot Tone–a patient study,” The International Journal of Cardiovascular Imaging, vol. 40, no. 1, pp. 93–105, 2024.
  2. J. Varghese, N. Jin, D. Giese, C. Chen, Y. Liu, Y. Pan, N. Nair, M. T. Shalaan, M. Khan, M. S. Tong, et al., “Building a comprehensive cardiovascular magnetic resonance exam on a commercial 0.55 T system: A pictorial essay on potential applications,” Frontiers in Cardiovascular Medicine, vol. 10, p. 1120982, 2023.
  3. D. Tucker, S. Zhao, R. Ahmad, and L. C. Potter, “Alias-free arrays,” IEEE Signal Processing Letters, vol. 29, pp. 2457–2461, 2022.
  4. S. K. Shastri, R. Ahmad, C. A. Metzler, and P. Schniter, “Denoising generalized expectation-consistent approximation forMR image recovery,” IEEE Journal on Selected Areas in Information Theory, vol. 3, no. 3, pp. 528–542, 2022.
  5. S. Zhao, R. Ahmad, and L. C. Potter, “Venc design and velocity estimation for phase contrast MRI,” IEEE Transactions on Medical Imaging, vol. 41, no. 12, pp. 3712–3724, 2022.
  6. C. Chen, P. Chandrasekaran, Y. Liu, O. P. Simonetti, M. Tong, and R. Ahmad, “Ensuring respiratory phase consistency to improve cardiac function quantification in real-time CMR,” Magnetic Resonance in Medicine, vol. 87, no. 3, pp. 1595–1604, 2022.
  7. H. Dong, R. Ahmad, R. Miller, and A. Kolipaka, “MR elastography inversion by compressive recovery,” Physics in Medicine & Biology, vol. 66, no. 16, p. 165001, 2021.
  8. D. Cristea, H. Wolfson, R. Ahmad, Y. Twig, P. Kuppusamy, and A. Blank, “Compact electron spin resonance skin oximeter: Properties and initial clinical results,” Magnetic Resonance in Medicine, vol. 85, no. 5, pp. 2915–2925, 2021.
  9. Zhao, L. C. Potter, and R. Ahmad, “High-dimensional fast convolutional framework (HICU) for calibrationless MRI,” Magnetic Resonance in Medicine, vol. 86, no. 3, pp. 1212–1225, 2021.
  10. A. Pruitt, A. Rich, Y. Liu, N. Jin, L. Potter, M. Tong, S. Rajpal, O. Simonetti, and R. Ahmad, “Fully self-gated whole-heart 4D flow imaging from a 5-minute scan,” Magnetic Resonance in Medicine, vol. 85, no. 3, pp. 1222–1236, 2021.
  11. M. A. Bush, Y. Pan, N. Jin, Y. Liu, J. Varghese, R. Ahmad, and O. P. Simonetti, “Prospective correction of patient-specific respiratory motion in myocardial T1 and T2 mapping,” Magnetic Resonance in Medicine, vol. 85, no. 2, pp. 855–867, 2021.
  12. D. A. Komarov, A. Samouilov, R. Ahmad, and J. L. Zweier, “Algebraic reconstruction of 3D spatial EPR images from high numbers of noisy projections: An improved image reconstruction technique for high resolution fast scan EPR imaging,” Journal of Magnetic Resonance, vol. 319, p. 106812, 2020.
  13. J. Varghese, M. Smyke, Y. Pan, S. Rajpal, J. Craft, L. C. Potter, S. V. Raman, R. Ahmad, and O. P. Simonetti, “Patient-adaptive magnetic resonance oximetry: Comparison with invasive catheter measurement of blood oxygen saturation in patients with cardiovascular disease,” Journal of Magnetic Resonance Imaging, vol. 52, no. 5, pp. 1449–1459, 2020.
  14. S. D. Serai, H. H. Hu, R. Ahmad, S. White, A. Pednekar, S. A. Anupindi, and E. Y. Lee, “Newly developed methods for reducing motion artifacts in pediatric abdominal MRI: tips and pearls,” American Journal of Roentgenology, vol. 214, no. 5, pp. 1042–1053, 2020.
  15. A. Rich, M. Gregg, N. Jin, Y. Liu, L. Potter, O. Simonetti, and R. Ahmad, “Cartesian sampling with variable density and adjustable temporal resolution (CAVA),” Magnetic Resonance in Medicine, vol. 83, no. 6, pp. 2015–2025, 2020.
  16. R. Ahmad, C. A. Bouman, G. T. Buzzard, S. Chan, S. Liu, E. T. Reehorst, and P. Schniter, “Plug-and-play methods for magnetic resonance imaging: Using denoisers for image recovery,” IEEE Signal Processing Magazine, vol. 37, no. 1, pp. 105–116, 2020. [long version (arxiv)]
  17. P. Kuppusamy, M. M. Kmiec, D. Tse, J. M. Mast, and R. Ahmad, “Estimation of pO2 histogram from a composite EPR spectrum of multiple random implants,” Biomedical Microdevices, vol. 22, no. 1, p. 3, 2020.
  18. J. Varghese, J. Craft, C. D. Crabtree, Y. Liu, N. Jin, K. Chow, R. Ahmad, and O. P. Simonetti, “Assessment of cardiac function, blood flow and myocardial tissue relaxation parameters at 0.35 T,” NMR in Biomedicine, vol. 33, no. 7, p. e4317, 2020.
  19. A. Rich, L. C. Potter, N. Jin, Y. Liu, O. P. Simonetti, and R. Ahmad, “A Bayesian approach for 4D flow imaging of aortic valve in a single breath-hold,” Magnetic Resonance in Medicine, vol. 81, no. 2, pp. 811–824, 2019.
  20. M. A. Bush, R. Ahmad, N. Jin, Y. Liu, and O. P. Simonetti, “Patient-specific prospective respiratory motion correction for efficient, free-breathing cardiovascular MRI,” Magnetic Resonance in Medicine, vol. 81, no. 6, pp. 3662–3674, 2019.
  21. M. Kmiec, D. Tse, J. Mast, R. Ahmad, and P. Kuppusamy, “Implantable microchip containing oxygen-sensing paramagnetic crystals for long-term, repeated, and multisite in vivo oximetry,” Biomedical Microdevices, vol. 21, no. 71, 2019.
  22. A. A. Pruitt, N. Jin, Y. Liu, O. P. Simonetti, and R. Ahmad, “A method to correct background phase offset for phase-contrast MRI in the presence of steady flow and spatial wrap-around artifact,” Magnetic Resonance in Medicine, vol. 81, no. 4, pp. 2424–2438, 2019.
  23. C. Chen, Y. Liu, P. Schniter, N. Jin, J. Craft, O. Simonetti, and R. Ahmad, “Sparsity adaptive reconstruction for highly accelerated cardiac MRI,” Magnetic Resonance in Medicine, vol. 81, no. 6, pp. 3875–3887, 2019.
  24. O. Zgadzai, Y. Twig, H. Wolfson, R. Ahmad, P. Kuppusamy, and A. Blank, “Electron-spin-resonance dipstick,” Analytical Chemistry, vol. 90, no. 13, pp. 7830–7836, 2018.
  25. A. Samouilov, R. Ahmad, J. Boslett, X. Liu, S. Petryakov, and J. L. Zweier, “Development of a fast-scan EPR imaging system for highly accelerated free radical imaging,” Magnetic Resonance in Medicine, vol. 82, no. 2, pp. 842–853, 2019.
  26. R. Ahmad, H. H. Hu, R. Krishnamurthy, and R. Krishnamurthy, “Reducing sedation for pediatric body MRI using accelerated and abbreviated imaging protocols,” Pediatric Radiology, vol. 48, no. 1, pp. 37–49, 2018.
  27. C. Ebersole, R. Ahmad, A. V. Rich, L. C. Potter, H. Dong, and A. Kolipaka, “A Bayesian method for accelerated magnetic resonance elastography of the liver,” Magnetic Resonance in Medicine, vol. 80, no. 3, pp. 1178–1188, 2018.
  28. J. S. da Silveira, M. Smyke, A. V. Rich, Y. Liu, N. Jin, D. Scandling, J. A. Dickerson, C. E. Rochitte, S. V. Raman, L. C. Potter, R. Ahmad, and O. P. Simonetti, “Quantification of aortic stenosis diagnostic parameters: comparison of fast 3 direction and 1 direction phase contrast CMR and transthoracic echocardiography,” Journal of Cardiovascular Magnetic Resonance, vol. 19, no. 1, p. 35, 2017.
  29. J. Varghese, L. C. Potter, R. LaFountain, X. Pan, S. V. Raman, R. Ahmad, and O. P. Simonetti, “CMR-based blood oximetry via multi-parametric estimation using multiple T2 measurements,” Journal of Cardiovascular Magnetic Resonance, vol. 19, no. 1, p. 88, 2017.
  30. S. T. Ting, R. Ahmad, N. Jin, J. Craft, J. Serafim da Silveira, H. Xue, and O. P. Simonetti, “Fast implementation for compressive recovery of highly accelerated cardiac cine MRI using the balanced sparse model,” Magnetic Resonance in Medicine, vol. 77, no. 4, pp. 1505–1515, 2017.
  31. O. P. Simonetti and R. Ahmad, “Low-field cardiac magnetic resonance imaging: A compelling case for cardiac magnetic resonance’s future,” Circulation: Cardiovascular Imaging, vol. 10, no. 6, p. e005446, 2017.
  32. R. Ahmad, A. Samouilov, and J. L. Zweier, “Accelerated dynamic EPR imaging using fast acquisition and compressive recovery,” Journal of Magnetic Resonance, vol. 273, pp. 105–112, 2016.
  33. A. Rich, L. C. Potter, N. Jin, J. Ash, O. P. Simonetti, and R. Ahmad, “A Bayesian model for highly accelerated phase-contrast MRI,” Magnetic Resonance in Medicine, vol. 76, no. 2, pp. 689–701, 2016.
  34. R. Ahmad, H. Xue, S. Giri, Y. Ding, J. Craft, and O. P. Simonetti, “Variable density incoherent spatiotemporal acquisition (VISTA) for highly accelerated cardiac MRI,” Magnetic Resonance in Medicine, vol. 74, no. 5, pp. 1266–1278, 2015.
  35. R. Ahmad and P. Schniter, “Iteratively reweighted l1 approaches to sparse composite regularization,” IEEE Transactions on Computational Imaging, vol. 1, no. 4, pp. 220–235, 2015. [constrained version (arxiv)]
  36. Y. Ding, H. Xue, R. Ahmad, T.-c. Chang, S. T. Ting, and O. P. Simonetti, “Paradoxical effect of the signal-to-noise ratio of GRAPPA calibration lines: A quantitative study,” Magnetic Resonance in Medicine, vol. 74, no. 1, pp. 231–239, 2015.
  37. R. Ahmad, Y. Ding, and O. P. Simonetti, “Edge sharpness assessment by parametric modeling: application to magnetic resonance imaging,” Concepts in Magnetic Resonance Part A, vol. 44, no. 3, pp. 138–149, 2015.
  38. H. Woflson, R. Ahmad, Y. Twig, B. Williams, and A. Blank, “A magnetic resonance probehead for evaluating the level of ionizing radiation absorbed in human teeth,” Health Physics, vol. 108, no. 3, pp. 326–335, 2015.
  39. D. H. Johnson, R. Ahmad, Y. Liu, Z. Chen, A. Samouilov, and J. L. Zweier, “Uniform spinning sampling gradient electron paramagnetic resonance imaging,” Magnetic Resonance in Medicine, vol. 71, no. 2, pp. 893–900, 2014.
  40. H. Wolfson, R. Ahmad, Y. Twig, P. Kuppusamy, and A. Blank, “A miniature electron spin resonance probehead for transcutaneous oxygen monitoring,” Applied Magnetic Resonance, vol. 45, no. 10, pp. 955–967, 2014.
  41. D. H. Johnson, R. Ahmad, G. He, A. Samouilov, and J. L. Zweier, “Compressed sensing of spatial electron paramagnetic resonance imaging,” Magnetic Resonance in Medicine, vol. 72, no. 3, pp. 893–901, 2014.
  42. J. A. Bender, R. Ahmad, and O. P. Simonetti, “The importance of k-space trajectory on off-resonance artifact in segmented echo-planar imaging,” Concepts in Magnetic Resonance Part A, vol. 42, no. 2, pp. 23–31, 2013.
  43. F. Golub, L. C. Potter, J. N. Ash, A. Blank, and R. Ahmad, “Estimation of spin-echo relaxation time,” Journal of Magnetic Resonance, vol. 237, pp. 17–22, 2013.
  44. R. Ahmad, S. Som, D. H. Johnson, J. L. Zweier, P. Kuppusamy, and L. C. Potter, “Multisite EPR oximetry from multiple quadrature harmonics,” Journal of Magnetic Resonance, vol. 214, pp. 135–143, 2012.
  45. J. Palmer, L. C. Potter, D. H. Johnson, J. L. Zweier, and R. Ahmad, “Dual-scan acquisition for accelerated continuous-wave EPR oximetry,” Journal of Magnetic Resonance, vol. 222, pp. 53–58, 2012.
  46. Y. Ding, H. Xue, R. Ahmad, S. T. Ting, and O. P. Simonetti, “SC-GRAPPA: Self-constraint noniterative GRAPPA reconstruction with closed-form solution,” Medical Physics, vol. 39, no. 12, pp. 7686–7693, 2012.
  47. R. Ahmad, L. C. Potter, and V. V. Khramtsov, “Spectral modeling for accelerated pH spectroscopy using EPR,” Journal of Magnetic Resonance, vol. 218, pp. 86–92, 2012.
  48. J. Palmer, L. C. Potter, and R. Ahmad, “Optimization of magnetic field sweep and field modulation amplitude for continuous-wave EPR oximetry,” Journal of Magnetic Resonance, vol. 209, no. 2, pp. 337–340, 2011.
  49. R. Ahmad and P. Kuppusamy, “Theory, instrumentation, and applications of electron paramagnetic resonance oximetry,” Chemical Reviews, vol. 110, no. 5, pp. 3212–3236, 2010.
  50. R. Ahmad, S. Som, E. Kesselring, P. Kuppusamy, J. L. Zweier, and L. C. Potter, “Digital detection and processing of multiple quadrature harmonics for EPR spectroscopy,” Journal of Magnetic Resonance, vol. 207, no. 2, pp. 322–331, 2010.
  51. R. Ahmad, G. Caia, L. C. Potter, S. Petryakov, P. Kuppusamy, and J. L. Zweier, “In vivo multisite oximetry using EPR–NMR coimaging,” Journal of Magnetic Resonance, vol. 207, no. 1, pp. 69–77, 2010.
  52. S. Som, L. C. Potter, R. Ahmad, D. S. Vikram, and P. Kuppusamy, “EPR oximetry in three spatial dimensions using sparse spin distribution,” Journal of Magnetic Resonance, vol. 193, no. 2, pp. 210–217, 2008.
  53. D. S. Vikram, R. Ahmad, B. K. Rivera, and P. Kuppusamy, “Mapping of oxygen concentration in biological samples using EPR imaging,” Israel Journal of Chemistry, vol. 48, no. 1, pp. 39–43, 2008.
  54. D. S. Vikram, R. Ahmad, R. P. Pandian, S. Petryakov, and P. Kuppusamy, “Evaluation of oxygen-response times of phthalocyanine-based crystalline paramagnetic spin probes for EPR oximetry,” Journal of Magnetic Resonance, vol. 193, no. 1, pp. 127–132, 2008.
  55. R. Ahmad, D. S. Vikram, L. C. Potter, and P. Kuppusamy, “Estimation of mean and median pO2 values for a composite EPR spectrum,” Journal of Magnetic Resonance, vol. 192, no. 2, pp. 269–274, 2008.
  56. R. Ahmad, B. Clymer, D. S. Vikram, Y. Deng, H. Hirata, J. L. Zweier, and P. Kuppusamy, “Enhanced resolution for EPR imaging by two-step deblurring,” Journal of Magnetic Resonance, vol. 184, no. 2, pp. 246–257, 2007.
  57. R. Ahmad, Y. Deng, D. S. Vikram, B. Clymer, P. Srinivasan, J. L. Zweier, and P. Kuppusamy, “Quasi Monte Carlo-based isotropic distribution of gradient directions for improved reconstruction quality of 3D EPR imaging,” Journal of Magnetic Resonance, vol. 184, no. 2, pp. 236–245, 2007.
  58. S. Som, L. C. Potter, R. Ahmad, and P. Kuppusamy, “A parametric approach to spectral–spatial EPR imaging,” Journal of Magnetic Resonance, vol. 186, no. 1, pp. 1–10, 2007.
  59. R. Ahmad, D. S. Vikram, B. Clymer, L. C. Potter, Y. Deng, P. Srinivasan, J. L. Zweier, and P. Kuppusamy, “Uniform distribution of projection data for improved reconstruction quality of 4D EPR imaging,” Journal of Magnetic Resonance, vol. 187, no. 2, pp. 277–287, 2007.
  60. D. S. Vikram, A. Bratasz, R. Ahmad, and P. Kuppusamy, “A comparative evaluation of EPR and oxylite oximetry using a random sampling of pO2 in a murine tumor,” Radiation Research, vol. 168, no. 3, pp. 308–315, 2007.
  61. Y. Deng, R. P. Pandian, R. Ahmad, P. Kuppusamy, and J. L. Zweier, “Application of magnetic field over-modulation for improved EPR linewidth measurements using probes with Lorentzian lineshape,” Journal of Magnetic Resonance, vol. 181, no. 2, pp. 254–261, 2006.
  62. R. Ahmad, B. Clymer, Y. Deng, G. He, D. Vikram, P. Kuppusamy, and J. L. Zweier, “Optimization of data acquisition for EPR imaging,” Journal of Magnetic Resonance, vol. 179, no. 2, pp. 263–272, 2006.
  63. R. Ahmad, D. S. Vikram, S. Petryakov, Y. Deng, J. L. Zweier, P. Kuppusamy, and B. Clymer, “Automated on-the-fly detection and correction procedure for EPR imaging data acquisition,” Magnetic Resonance in Medicine, vol. 56, no. 3, pp. 644–653, 2006.

Conference Publications

  1. M. Bendel, R. Ahmad, and P. Schniter, “A regularized conditional GAN for posterior sampling in image recovery problems,” Advances in Neural Information Processing Systems, vol. 36, 2024.
  2. J. Wen, R. Ahmad, and P. Schniter, “A conditional normalizing flow for accelerated multi-coil MR imaging,” Proceedings of Machine Learning Research, vol. 202, p. 36926, 2023.
  3. S. K. Shastri, R. Ahmad, C. A. Metzler, and P. Schniter, “Expectation consistent plug-and-play for MRI,” in International Conference on Acoustics, Speech and Signal Processing (ICASSP), pp. 8667–8671, IEEE, 2022.
  4. S. Liu, P. Schniter, and R. Ahmad, “MRI recovery with a self-calibrated denoiser,” in International Conference on Acoustics, Speech and Signal Processing (ICASSP), pp. 1351–1355, IEEE, 2022.
  5. S. Zhao, R. Ahmad, and L. C. Potter, “Maximizing unambiguous velocity range in phase-contrast MRI with multipoint encoding,” in 19th International Symposium on Biomedical Imaging (ISBI), pp. 1–5, IEEE, 2022.
  6. S. Sarkar, R. Ahmad, and P. Schniter, “MRI image recovery using damped denoising vector AMP,” in ICASSP 2021 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), pp. 8108–8112, IEEE, 2021.
  7. S. Zhao, L. C. Potter, and R. Ahmad, “Calibrationless MRI reconstruction with a plug-in denoiser,” in 2021 IEEE 18thInternational Symposium on Biomedical Imaging (ISBI), pp. 1846–1849, IEEE, 2021.
  8. S. K. Shastri, R. Ahmad, and P. Schniter, “Autotuning plug-and-play algorithms for MRI,” in 2020 54th Asilomar Conference on Signals, Systems, and Computers, pp. 1400–1404, IEEE, 2020.
  9. S. Liu, E. Reehorst, P. Schniter, and R. Ahmad, “Free-breathing cardiovascular MRI using a plug-and-play method with learned denoiser,” in 2020 IEEE 17th International Symposium on Biomedical Imaging (ISBI), pp. 1748–1751, IEEE, 2020.
  10. S. Zhao, L. C. Potter, K. Lee, and R. Ahmad, “Convolutional framework for accelerated magnetic resonance imaging,” in 2020 IEEE 17th International Symposium on Biomedical Imaging (ISBI), pp. 1–4, IEEE, 2020.
  11. C. Chen, Y. Liu, O. P. Simonetti, and R. Ahmad, “Automatic extraction and sign determination of respiratory signal in real-time cardiac magnetic resonance imaging,” in 2020 IEEE 17th International Symposium on Biomedical Imaging (ISBI),pp. 1–4, IEEE, 2020.
  12. A. Rich, L. C. Potter, J. N. Ash, and R. Ahmad, “Factor graphs for inverse problems: Accelerated phase contrast magnetic resonance imaging,” in 2015 IEEE International Conference on Image Processing (ICIP), pp. 1026–1030, IEEE, 2015.
  13. H. Wolfson, R. Ahmad, Y. Twig, A. Blank, and P. Kuppusamy, “A hand-held EPR scanner for transcutaneous oximetry,” in Medical Imaging 2015: Biomedical Applications in Molecular, Structural, and Functional Imaging, vol. 9417, p. 941706, International Society for Optics and Photonics, SPIE, 2015.
  14. R. Ahmad, C. Austin, and L. C. Potter, “Toeplitz embedding for fast iterative regularized imaging,” in Algorithms for Synthetic Aperture Radar Imagery XVIII, vol. 8051, p. 80510E, International Society for Optics and Photonics, SPIE, 2011.
  15. R. Ahmad, P. Kuppusamy, and L. C. Potter, “Nested uniform sampling for multiresolution 3-D tomography,” in 2010 IEEE International Conference on Acoustics, Speech and Signal Processing, pp. 461–464, IEEE, 2010.