Stephan Maier, MD, PhD: The Quest for Quantitative Parameters in Magnetic Resonance Imaging

Stephan Maier, MD, PhD
Associate Professor
Department of Radiology,
Brigham and Women’s Hospital
Harvard Medical School

Abstract

Numerous quantitative parameters, such as spatial dimensions, volume, nuclear magnetic resonance relaxation, velocity, and diffusion can be measured with magnetic resonance imaging. Many of these quantitative parameters could be highly useful biomarkers, particularly if followed over time, to differentiate normal from disease. Presently, however, these biomarkers have found very limited adoption in clinical practice. The reasons are manyfold. Unlike a blood test that delivers a single value, with magnetic resonance imaging the quantitative parameter is generated for each of many image voxels and a clinically meaningful biomarker may have to be derived by cumbersome, expertise-demanding, region-of-interest analysis. Other limitations, that also impede reproducibility among scanners, are inaccuracies because of spatially non-uniform sensitization and oversimplified assumptions about the relationship between desired sensitization and the actually measured parameter. Also, while for some parameters like spatial dimensions, volume, or velocity the underlying physical meaning is straightforward, the extended physical interpretation of other parameters like relaxation or diffusion is less obvious. Decades of research have brought a better understanding and an armamentarium to efficiently deal with this complexity, even in view of the constraints of scan time, a limitation that cannot be relaxed when scanning patients. In this presentation novel solutions for truly reproducible and more robust diffusion quantification will be presented. Potentially these solutions can contribute to a more ubiquitous deployment of quantitative parameters for clinical decision making, particularly if combined with neural networks for faster processing and automated region-of-interest analysis.

Short Bio

Stephan Maier received his medical degree in 1985 from the University of Zurich, Switzerland. Subsequently he completed his Doctor of Medicine at the University of Zurich with a dissertation on comparative studies with magnetic resonance and Doppler ultrasound for quantification of blood velocity and flow in the human abdominal aorta. This was followed by a dissertation on motion sensitive magnetic resonance techniques at the Federal Institute of Technology (ETH) Zurich where in 1992 he received his Doctor of Natural Sciences. He continued his research at Brigham and Women’s hospital in Boston, MA. There he developed the widely used line scan diffusion imaging (LSDI) magnetic resonance pulse sequence. This novel technique provided robust and largely artifact-free diffusion images on the magnetic resonance imaging systems available at the time. It also lead to numerous research studies that were ground breaking in revealing the complexity of the measured water diffusion related signal decay in normal and diseased tissues, with applications in neonatology, psychiatric disorders, brain tumors, and prostate cancer. From 2014 until 2022 he spent significant time at the Gothenburg University, Sweden, where he supervised a group of investigators for further development of reliable and reproducible diffusion imaging techniques. Recently he has returned for a full time commitment to Brigham and Women’s Hospital, with particular focus to promote cutting edge diffusion imaging facilities and techniques for application in tumor imaging and in the context of the hospital’s National Center for Image Guided Therapy (AT-NCIGT). Throughout his professional career he has received continuous research funding support from private foundations and state agencies, including the National Institutes of Health.