Practice question

Functional magnetic resonance imaging exploits endogenous contrast from hemoglobin oxygenation state without exogenous tracer. Deoxyhemoglobin contains four unpaired electrons in ferrous heme, making it paramagnetic, distorting local magnetic field and accelerating transverse relaxation, reducing T2* signal. Oxyhemoglobin with bound oxygen is diamagnetic and preserves homogeneity. Activation increases cerebral blood flow delivering excess oxyhemoglobin, lowering deoxyhemoglobin concentration and enhancing MRI intensity. Computed tomography relies on X-ray attenuation, EEG records voltage, PET senses positron decay, none sense magnetic properties of hemoglobin differently.