Chapter 4: Self-assessment Questions

 

  1. What is an image? What do MR images represent?
  2. Explain the following equation in simple language:

Mz = Mo + (Mzo – Mo) · e–t/T1

  1. What happens to transverse magnetization over time as a result of T2 decay?
  2. Why do we want to collect images at intermediate times of T­1 recovery and T2 decay? That is, why can’t we collect our images immediately following excitation (or a very long time after excitation) and still get T1 or T2 contrast?
  3. Explain the following sentence:

The total signal measured in MRI combines the changes in net magnetization generated at every excited voxel.

  1. Why are magnetic field gradients important for image formation?
  2. What is slice selection? How is it typically accomplished in MRI?
  3. What is k-space? How is k-space different from normal image space?
  4. What does the center of k-space represent? What does the periphery of k-space represent?
  5. What is reconstruction?
  6. If we want to have an image with a higher spatial resolution, how must we change our sampling of k-space? What if we want an image with a larger field of view?
  7. Why do most fMRI imaging sequences use interleaved slice acquisition?
  8. How is spatial information encoded within a single slice?
  9. Why do gradient inhomogeneities cause stretching or skewing of images? Refer to the concept of k­-space in your answer.