Magnetic Resonance Imaging (MRI) Practice Test

How does a steep slice select slope and/or narrow bandwidth affect slice thickness?

1. Slices will be thick

2. Slices will be thin

3. Slices will remain unchanged

4. Slices will become wider

The correct answer is: Slices will be thin

A steep slice select slope and a narrow bandwidth contribute to producing thinner slices in MRI. The slice thickness in MRI is influenced by the slice selection gradient and the radiofrequency (RF) bandwidth applied during imaging. When the slope of the slice selection gradient is steep, it indicates a rapid change in the magnetic field within a shorter distance. This steep gradient means that the frequency encoding of the signals can occur over a limited range, allowing for greater precision in choosing a specific slice of tissue. Consequently, the ability to define the slice is enhanced, resulting in thinner slices. Similarly, narrowing the bandwidth effectively reduces the range of frequencies that the RF pulse excites. A lower bandwidth translates to a more focused selection of spins in the designated slice, further leading to a reduction in slice thickness. In summary, both a steep slice select slope and a narrow bandwidth enable the imaging system to more accurately isolate thinner segments of tissue, which is why the slices become thin under these conditions.