Q. Which of the following best describes the appearance of an acute ischaemic infarct of the brain?
a. Hypointense on diffusion-weighted (DW) MRI and low apparent diffusion coefficient (ADC) values.
b. Hyperintense on DW MRI and low ADC values
c. Hypointense on DW MRI and high ADC values
d. Hyperintense on DW MRI and high ADC values
ANSWER:
dint got it sir ..
ReplyDeleteplease explain
To understand this , you will need some MRI physics which itself might be confusing.
ReplyDeleteStill i am posting it here.
DW images are MR images that are created by applying a pair of magnetic gradient pulses that sensitize the sequence to motion. By applying very large gradients and allowing sufficient time to pass between gradient lobes (pulses), one can sensitize the scan to microscopic motions that are occurring within the imaging voxel.
The amount of diffusion weighting of a DW image is determined by the magnitude of the applied gradients, how long they are switched on, and the time between the two lobes. The magnitude of diffusion weighting is connoted by the “b” value of the image. Typical “b” values (in seconds per square millimeter) for imaging stroke are on the order of 400 to 1000 sec/mm2. By comparing diffusion-sensitizing gradients (i.e., the “b zero” image), one can compute the amount of diffusion that appears to have occurred. If this is done on a pixel-by-pixel basis, the result is a computed map of apparent diffusion known as an ADC map.
DW images are highly sensitive to the diffusion restriction that occurs in acute stroke. Regions of acute cerebral ischemia are typically hyperintense on DW images and result in diminished ADC values of up to 40%.
It is often assumed that hyperintense signal on DW images represents irreversible ischemia. However, studies of experimental stroke and some depicted on imaging studies represent potentially reversible ischemia.
I would suggest all to mug up the answer if you do not understand the explanation because the Acute Ischemic Infarct is an important topic.
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