What is the maximum strength of magnet approved for medical imaging of patients?
ID: 2034074 • Letter: W
Question
What is the maximum strength of magnet approved for medical imaging of patients?
7T
5T
3T
1.5T
What does precession mean?
The spinning of hydrogen protons around their own axis.
The change in orientation of hydrogen molecules when exposed to radiowaves at the Larmor frequency.
The wobble of hydrogen protons exposed to a large magnetic field.
Water molecules gain an extra molecule of hydrogen when exposed to a magnetic field.
Which of these is a disadvantage of MRI?
High dose of ionizing radiation.
Shows vasculature without contrast
Unsuitable for pacemaker wearers
Two-dimensional images
In MRI the resonant frequency of a specific tissue is NOT determined or affected by the:
Specific isotope being imaged
Characteristics of the molecule
Orientation of magnetic field
Strength of the magnetic field
Explanation / Answer
No adverse effects are expected if fields do not exceed the following Medicines and Healthcare products Regulatory Agency (MHRA) guidelines for whole body exposure of patients:
Normal mode: less than 2.5T
Controlled mode: between 2.5T and 4T
Research and experimental mode: more than 4T.
Pregnant patient should not be exposed above 2.5T.
The patient’s electrocardiogram is affected above 0.3T but returns to normal after exposure. Above 4T, adverse bio effects may occur.
In an external magnet field the proton present in the tissues are getting align along the applied magnetic field. The proton’s spin start precession or wobble around the exposed magnetic field.
In general the MRI is not suitable for patient wearing pacemaker.
The resonant frequency depends only on the protons present in the molecule of tissues. Hence for the isotope molecules having same number of protons will have same resonant frequency. So resonant frequency is not determined or affected by the specific isotopes being imaged.
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