MRI PHYSICS- Armrit Test Questions and Answers (Graded A)
7 views 0 purchase
Course
MRI PHYSICS- Armrit
Institution
MRI PHYSICS- Armrit
MRI PHYSICS- Armrit Test Questions and Answers (Graded A)
MRI PHYSICS- Armrit Test Questions and Answers (Graded A)
MRI PHYSICS- Armrit Test Questions and Answers (Graded A)
Signal - ANSWER-Current induced iby receiver coil. Also comes from the procession of protons in the patient.
Ch...
MRI PHYSICS- Armrit Test Questions and Answers (Graded A)
Signal - ANSWER-Current induced iby receiver coil. Also comes from the procession of protons in the patient.
Chemical pre saturation - ANSWER-Selectively apply 90 degree pulse at frequency of tissue to be saturated. Moves fat or HBO 90 degrees. 2nd puse wider bandwidth moves
both fat and water 90 degrees. One will be saturated so will not be read. Saturating out normal anatomy, pathology is often seen more clearly.
NEX number of excitations - ANSWER-is the number of times each line is filled with the data in K space, the number of times and echo is encoded with the same slope of phase encoding gradient.
NEX (number of excitations) to increase (SNR) - ANSWER-signal strength is proportional to square root. To double SNR you increase __________ and scan time by
factor of four.
Scan time is proportional to - ANSWER-TR, phase matrix the number of encodings, NEX doubling all of these doubles times.
Rise time - ANSWER-Time required for MRI machine to reach field strength for gradient. Steeper slope longer time.
Receive bandwidth to increase signal (SNR) - ANSWER-Decrease this and you have better SNR
Proton density weighed images - ANSWER-Long TR, short T, small flip angle highest signal to nose ratio.
Magnetization transfer contrast (MTC) - ANSWER-Technique used to suppress bound protons by saturating them before the excitation pulse. This reduces the signal in free protons. This increases the contrast (CNR) between normal pathological tissues. Good in angiography and joint imaging.
What effects voxel size - ANSWER-Slice thickness (slope of the gradient), FL , the matrix (#of encodings)
Voxel volume to increase signal (SNR) - ANSWER-Lager voxel more signal (SNR), thicker slicers, larger FOV more in picture, smaller image matrix (determines amount of pixels) TR (repetition time) - ANSWER-Controls recovery of longitudinal magnetization. Increasing also increases scan time.
TR to increase signal (SNR) - ANSWER-Long, lots of recovery, larger signal (SNR). Full
recovery allows most signal to be rotated into transverse plane.
Pixel shape is rectangular when - ANSWER-FOV square and scan matrix odd FOV rectangular and scan matrix is even.
TE (echo time) to increase signal (SNR) - ANSWER-Shorter time better signal. Allows less dephasing.
Spacial resolution - ANSWER-The ability to distinguish between two points. It is controlled by voxel size. Put structures in separate voxels, smaller voxels, thinner slices,
steeper gradient, smaller FOV, fine matrix, rectangular FOV. Poor SNR = better resolution.
( 1 ) Noise - ANSWER-(1) Anything that interferesays with, distortso or slows down the tamale of information. (MRI machine, non signal pickup from receiver coil)
Contrast to noise ratio (CNR) - ANSWER-Difference in SNR in adjacent regions indicate
amount of contrast S/Np1-S/Np2. Can be increased by T2 weighed image, chemical pre
saturation, (MAG) magnetization transfer contrast and contrast agent.
Coil to increase signal (SNR) - ANSWER-Type and position, best to position transverse to Bo
Bound proton - ANSWER-Protons that are bound to large proteins, members and other macromolecules
3 volume imaging - ANSWER-Taking picture then slice after picture is done. Use with complicated anatomy ligaments joints. Long scan tone, no slice selection-slice encoding, finger sliceso no gaps.
(1) Signal to noise ratio (SNR) - ANSWER-(1)Amplitude of the signal/ the amplitude of noise want the number to be large.
(2) Signal to noise ratio (SNR) - ANSWER-(2) The strength/ as compared with the nose level. Contrast resolution improve the nose level. Contrast resolution improve as the SNR is increased.
How can you increase signal (SNR) - ANSWER-Extrinsic: TR, TE, flip angle, NEX, coil type, receive bandwidth.
Intrinsic: field strength, proton density, voxel volume, T1, T2 time.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller NursingTutor1. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $10.99. You're not tied to anything after your purchase.
