Session Z51: Physics Enabled Medical Devices

MRI Standardization for Quantitative Disease Biomarkers: implementation to clinical studies and trials

Magnetic Resonance Imaging (MRI) offers a natural, quantitative way of characterizing soft tissues in health and disease. With the development of the MRI field, the quantitative aspect was dropped in favor of qualitative, contrast-based imaging approaches. In recent years a renewed interest in quantitation in MRI has emerged, enabled by the development of new ideas for shortening the length of qMRI scans rivaling contrast-based approaches. The absolute categorization of tissue is based on quantitative biomarkers established in clinical studies and trials. The major biomarkers are based on MR tissue properties - longitudinal T1 and transverse T2 relaxation times, diffusion properties – Apparent Diffusion Coefficient (ADC), etc. A significant obstacle in adopting clinical qMRI methodologies is the variability of the quantitative output within and across manufacturers. CaliberMRI (CMRI) is on a quest to standardize scanner lateral and longitudinal performance using quantitative Reference MRI Mimics. The mimics are standardized by the NIST and qCal, a CMRI software platform for comprehensive QA/QC analysis. We will present a use case of standardization of ADC as a breast cancer biomarker in neoadjuvant therapy monitoring in I-SPY2 clinical trial.   

Photoacoustic tomography beyond the optical diffusion limit and compressed ultrafast photography at light speed

We developed photoacoustic tomography (PAT) to peer deep into biological tissue. PAT provides in vivo functional, metabolic, molecular, and histologic imaging across the scales of organelles through organisms. We also developed compressed ultrafast photography (CUP) to record 70 trillion frames per second, orders of magnitude faster than commercially available camera technologies. CUP can record in real time the fastest phenomenon in nature, namely, light propagation, and can be slowed down for slower phenomena such as neural conduction.

PAT physically combines optical and ultrasonic waves. Conventional high-resolution optical imaging of scattering tissue is restricted to depths within the optical diffusion limit (~1 mm). PAT beats this limit and provides deep penetration at high ultrasonic resolution and high optical contrast by sensing molecules. Broad applications include early-cancer detection and brain imaging. The annual conference on PAT has become the largest in SPIE’s 20,000-attendee Photonics West since 2010.

CUP with a single exposure can image transient events occurring on a time scale down to 10s of femtoseconds. Akin to traditional photography, CUP is receive-only—avoiding specialized active illumination required by other single-shot ultrafast imagers. CUP can be coupled with front optics ranging from microscopes to telescopes for widespread applications in both fundamental and applied sciences, ranging from biology to cosmophysics.

    

Advantages and Challenges of Magnetic Resonance Image Guidance for Radiation Therapy

Magnetic Resonance Imaging (MRI) has high soft-tissue contrast and allows for real-time imaging with no ionizing radiation dose to the patient, making it an ideal modality for monitoring patient organ and tumor motion during radiation therapy treatments. However, MRI requires a high-strength, highly homogeneous magnetic field, which is difficult to achieve in proximity to medical linear accelerators, which produce electromagnetic fields of their own and are often in motion during treatment. The result of this pairing is that MRI-guided radiation therapy faces unique challenges and tradeoffs between imaging and treatment capabilities. This talk provides an overview of the complications that arise when combining these two technologies as well as the advantages that make it worth the effort, with a focus on our experience with the Viewray MRIdian platform at New York Presbyterian Hospital.   

Photon-counting-detector CT: Technology and clinical applications

Photon-counting-detector CT (PCD-CT) has emerged as a new clinical CT platform with many potential advantages over conventional energy-integrating-detector CT (EID-CT). This talk will provide an overview of the PCD-CT technology and various clinical applications that may benefit from it. Different from EID-CT, the photon-counting detection mechanism in PCD-CT provides more signals and more spectral information about the materials. Potential advantages of PCD-CT include improved radiation dose efficiency, improved spatial resolution, and simultaneous multi-energy multi-contrast agent imaging.   

Transcranial Magnetic Stimulation: A non-invasive neuromodulation technique for altering neuronal networks in the brain

Transcranial Magnetic Stimulation (TMS) can tune brain functions non-invasively, safely, and effectively without the need for surgery or drugs. Thus, it can enable the treatment of several debilitating neurological obsessive-compulsive disorders, and migraine [1]. My lab has designed and fabricated an anatomically accurate human brain phantom that can be used to test the feasibility and safety of several TMS protocols. We have investigated a feasibility study of combined TMS and DBS using brain phantom in collaboration with the VCU Dept. of Neurosurgery [2], [3]. We have also designed and fabricated novel focal stimulation coils based on novel soft ferromagnetic materials that can stimulate only a local region of the primary motor cortex. We are currently working to experimentally verify the results from coil design in rats in collaboration with the Dept. of Neurology at VCU [4]. We are also working to establish an accurate mechanism underlying TMS by investigating the neuronal firing patterns in several brain regions induced by cortical stimulation and by establishing the role of individual nuclei in affecting other nuclei of the motor circuitry. My team has also designed a TMS coil configuration that can stimulate multiple sites simultaneously and vary sites of stimulation without moving the coils physically. These new TMS techniques will enable the future development of effective TMS protocols for the diagnosis and treatment of several neurological and psychiatric disorders.

References: 

[1]  S. Rossi et al., “Safety and recommendations for TMS use in healthy subjects and patient populations, with updates on training, ethical and regulatory issues: Expert Guidelines,” Clin. Neurophysiol., 132, p. 269, 2021.

[2]  H. Magsood, et al., Front. Hum. Neurosci., 14, p. 123, 2023.

[3] H. Magsood and R. L. Hadimani, Mater. Sci. Eng. C, 120, p. 111705, 2021.

[4] I. C. Carmona, D. Kumbhare, M. S. Baron, and R. L. Hadimani,  AIP Adv., 11,  p. 025210, 2021.