Final answer:
The slice-select gradient in MRI is used to target a specific section of the body for imaging. Without it, the MRI can't produce clear, localized images, leading to non-diagnostic results and an inability to assist in medical diagnoses.
Step-by-step explanation:
The slice-select gradient in magnetic resonance imaging (MRI) is a crucial component used to select a specific slice or section of the body for imaging. When the MRI system is turned on, the slice-select gradient is applied along one axis of the body (typically the z-axis), allowing the magnetic field to vary linearly along that axis. By combining the gradient with the radiofrequency (RF) pulse, it is possible to excite protons only in a certain plane of the body that corresponds to a specific frequency, essentially 'selecting' the preferred slice to be imaged.
If the slice-select gradient does not turn on, the MRI system will not be able to localize the imaging to the particular section of the body that is meant to be scanned. This means that the MRI machine would not acquire useful images as it cannot differentiate between signals from various slices. The result would be a failure in generating the desired diagnostic images, as the machine might capture signals from the entire volume rather than the targeted slice. This leads to a non-diagnostic image, which cannot be used effectively by medical professionals to diagnose conditions.