This set of Clinical Science Multiple Choice Questions & Answers (MCQs) focuses on “MRI”.
1. The commonly used MRI’s have a magnetic strength of ______
a) 1.5 – 3 Tesla
b) 3 – 6 Tesla
c) 6 – 12 Tesla
d) 12 – 24 Tesla
View Answer
Explanation: MRI’s have three major portions which work together to form an image. The largest portion is taken up by the magnet. This magnet is always on and produces a Magnetic Field of the strength of 1.5 – 3 Tesla. Commercially, 1.5 – 2 T was used but now even with 3T have been introduced. For research purposes, MRI of 7T has also been constructed.
2. The cooling agent for the MRI magnet is _______
a) Helium
b) Neon
c) Argon
d) Xenon
View Answer
Explanation: Helium is a noble gas which is non reactive in nature. A good coolant has a high thermal capacity, low viscosity, non toxic, chemically inert, all the properties that Helium possesses. Another advantage is that Helium does not have the tendency to absorb any neutrons and so it cannot become radioactive. Being a noble gas, it is non reactive and so non corrosive in nature. Thus, it is used a coolant for the MRI machine, especially the magnet.
3. If an MRI was done for a long bone, the part of the bone that will be imaged is the _________
a) Bone salts
b) Bony Prominence
c) Inflamed Joints
d) Bone Marrow
View Answer
Explanation: Bone marrow is a soft tissue as compared to the encasing bone structure. Also, it had water whose Hydrogen is used by the MRI to form an image. The other parts of the bone do contain hydrogen but the hydrogen is placed in a crystal structure, making it difficult to move or be magnetized. Thus, it is difficult to image any other parts of the bone with MRI except for the bone marrow.
4. A hypothetical MRI is made having a magnetic field (B0) of 7 Tesla. This uses nitrogen for study. The gyrometric ratio of nitrogen 15 is -4.316. Find the Lamar frequency.
a) -35.889
b) – 30.212
c) 0
d) -189.812
View Answer
Explanation: Gyrometric ratio is the ratio of the magnetic moment to the angular moment of the element. Lamar frequency, also called as Lamar precision is the frequency by which the element will undergo a change in orientation when placed in a strong external magnetic field. Lamar frequency is given by the formula: f = γn x B0/2Π
Here γn/2Π is the gyrometric ratio. Thus,
f = -4.316*7 = -30.212.
5. If the XY grid is selected in MRI then the slice selection is in which plane?
a) X plane
b) Y plane
c) Z plane
d) XY plane
View Answer
Explanation: An MRI can give a 3D image of an object and we can choose the form which direction and from which angle we would like to view the image. The image is always perpendicular to the grid that has been selected. As it is given that our grid is XY, then slice selection can be done only in Z plane and so, therefore, the image is also in Z plane.
6. The smallest unit in the reconstruction/projection of an MRI image is called as ________
a) pixel
b) voxel
c) binary unit
d) dot
View Answer
Explanation: Voxel stands for the volumetric pixel. MRI is unique in a way that it can image segments of the organ from different angles with various slice selections. These slice selections help choose which layer of the organ will be imaged and the smallest unit of this image is called a voxel. Since MRI can produce 3D scans, the image is volumetric in nature and thus, volumetric pixel or voxel is used.
7. MRI has a high _______ resolution.
a) spatial
b) temporal
c) frequency
d) magnitude
View Answer
Explanation: MRI can form a 3D image of the organ which is anatomical in nature. It gives good clarity and resolution for the finer details of the image. In the same way, fMRI has a good temporal resolution. It maps the brain with respect to time, scanning the oxygen used at the regular intervals.
8. In a brain scan of a person suffering/suspected of suffering from schizophrenia, the brain _______
a) has gray matter which more than normal
b) has white matter which more than normal
c) is of a size bigger than normal
d) has shrunk
View Answer
Explanation: A person suffering from schizophrenia suffers from problems like hallucinations, listening to non existent sounds etc. The persistent problem can be analyzed by looking at the brain scan which shows that the white matter in a particular part of the brain has become more than normal. Since white matter is responsible for sending impulses, a bigger area of white matter will mean faster travelling of impulses and therefore such thoughts. However, since the CT shows the negatives of the original, the white matter will look gray and gray matter will look white. Thus, in a scan, if there is a large gray area and the person suffers from symptoms like hallucinations or anxiety etc, then it’s a high possibility that they have schizophrenia.
9. The scans for lissencephaly will show a brain _______
a) with no gyri and sulci
b) with excess gyri and sulci
c) with deformed brain structure
d) with a smaller than normal brain size
View Answer
Explanation: Lissencephaly is a neuronal defect that is present right from birth. It may or may not be detected in the fetal stage. In this disorder, the brain in smooth without the presence of any gyri and sulci. A child born with lissencephaly often has a normal head structure so it is often difficult to detect the presence of this defect till a later age.
10. Frontotemporal Dementia brain scan shows a __________
a) growing brain
b) shrinking brain
c) brain with lesions
d) brain with a tumour
View Answer
Explanation: Frontotemporal Dementia (FTD) is the most common kind of dementia found in the population. In this, the neural cells of the brain go for apoptosis (cell death) causing an atrophy (shrinkage) of the brain. This causes the person to have memory disorders.
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