Urology>>>>>Imaging and Principles of Uro-Radiology
Question 5#

Which of the following statements is INCORRECT?

A. T1-weighted MRI images show water to be dark
B. T2-weighted MRI images show water to be bright
C. Gadolinium uptake in tissues makes them appear brighter on T1-weighted MRI images
D. Neutrons in the nucleus of the hydrogen atom have a negative charge
E. Gadolinium should not be given if eGFR is less than 30 mL/min/1.73 m2 due to risk of nephrogenic systemic fibrosis

Correct Answer is D

Comment:

Answer D

MRI uses the magnetic properties of hydrogen and its interaction with both a large external magnetic field and radio waves to produce highly detailed images of the human body. The nucleus of an atom consists of protons (positive charge) and neutrons (neutral charge). The most common Hydrogen atom isotope in the human body (Protium) has a single proton in its nucleus and no neutrons. The protons are in motion and spin about their axis. When placed in a magnetic field, the protons always align either parallel or anti-parallel to the direction of the magnetic field. When excited by a radio wave they flip direction. Over time, they flip back, emitting a radio signal (MR signal), which is captured by the scanner.

T1 represents longitudinal relaxation time. This indicates the time required for a substance to become magnetised after first being placed in a magnetic field. This involves a transfer of energy. T1-weighted MR images show fat to be bright and water dark. T2 is the transverse relaxation time (decay). It is a measure of how long transverse magnetisation would last in a perfectly uniform external magnetic field. T2-weighted MR images show fluid/water to be bright and fat to be intermediate to dark.