Speakers:
Eva Anderson (Carleton University)
Toward more accurate gas-free calibration of the blood oxygenation level-dependent (BOLD) signal: Separating vascular from nonvascular sources of magnetic susceptibility
The blood oxygenation level-dependent (BOLD) signal is the most common functional MRI technique for mapping brain organization in humans. It is naturally a qualitative measure that reflects changes in oxygen metabolism and blood flow that are driven by changes in brain activity. By calibrating the BOLD signal, we can obtain quantitative measurements of oxygen metabolism. Calibration is typically done by means of a gas challenge, where a subject undergoes an fMRI scan at rest as well as a scan while breathing room air mixed with carbon dioxide or additional oxygen. From this, a subject-specific map of calibration parameters is obtained. Recently, a gas-free method has been proposed to obtain this calibration parameter by measuring R2’, the reversible component of the transverse relaxation rate which arises from field inhomogeneities. However, in addition to paramagnetic hemoglobin, which we are interested in, R2’ is sensitive to many sources of magnetic susceptibility from other tissues, such as iron depositions and myelin.
Our goal is to determine to what extent these other sources of susceptibility influence and contribute to the total magnetic susceptibility of a voxel and the bias they create in R2’-based calibration. In this work, we used quantitative susceptibility maps measured in participants at rest and during a gas challenge to determine how much the vasculature contributes to magnetic susceptibility compared to other tissues.
Spencer Manwell (Convergent Imaging Solutions)
Personalized treatment planning in radionuclide therapy: the new old kid in town.
Pharmaceuticals used for therapy involving radioactive substances have been in use for many decades. One of the earliest and most widely used being Iodine-131 for the treatment of benign and malignant thyroid diseases. More recently, the field of nuclear medicine has been gripped by the concept of personalized (or precision) medicine and advances in radiochemistry, leading to the development of new radiopharmaceuticals designed for therapeutic purposes. These two shifts are causing some researchers and clinicians to raise questions about the traditional dosing strategies that were designed for radiopharmaceuticals like Iodine-131 and whether we can do better going forward.
In this talk, I'll take a look at the current landscape of radionuclide therapy and how absorbed dose calculations are being proposed to plan individual patients' treatments in place of the long-standing empirical dosing strategies. My review will cover some of the modern approaches used for dose calculation, the challenges associated with them, and why the nuclear medicine field is reluctant to follow the footsteps of radiation oncology in requiring individual treatment planning for all patients.