MRI Physics Quiz 2 Latest Version Already Graded A

MRI Physics Quiz 2 Latest Version Already Graded A What is the primary function of the main magnetic field in MRI? To align hydrogen protons in the body What happens when an RF pulse is applied during an MRI scan? It excites hydrogen protons, causing them to move out of alignment What is the purpose of gradient coils in MRI? To spatially encode signals by varying the magnetic field Why is T2 relaxation important in MRI? It helps differentiate tissues based on their transverse magnetization decay What factor determines the Larmor frequency of hydrogen protons? The strength of the magnetic field 2 Why does fat appear bright on T1-weighted images? Fat has a short T1 relaxation time, leading to high signal intensity What role does TR (Repetition Time) play in MRI imaging? It controls the amount of longitudinal relaxation before the next RF pulse How does increasing TE (Echo Time) affect image contrast? It enhances T2-weighted contrast by allowing more transverse relaxation Why is a 90-degree RF pulse commonly used in spin-echo sequences? It maximizes signal generation by flipping protons into the transverse plane What is the function of a 180-degree refocusing pulse in spin-echo sequences? It compensates for field inhomogeneities and reduces signal loss Why is T1-weighted imaging useful in MRI? It provides excellent anatomical detail and differentiation between fat and water 3 How does increasing the number of signal averages (NEX) improve image quality? It reduces noise, improving signal-to-noise ratio What is the relationship between voxel size and spatial resolution in MRI? Smaller voxels improve spatial resolution but may reduce signal intensity Why is a short TR used in T1-weighted imaging? To highlight tissue differences in longitudinal relaxation times What happens to the MRI signal when proton dephasing occurs? The signal decreases due to loss of phase coherence Why is T2* relaxation faster than T2 relaxation? T2* includes additional signal loss from field inhomogeneities and susceptibility effects What is the primary cause of chemical shift artifacts in MRI? Differences in resonance frequencies between fat