Clin rad lectures: CT and MRI

Question 1

Advanced Imaging Modalities: CT

Answer 1

Pixels (picture elements) = small squares of data that make up image we see on axial data
Voxels (volume elements) = pixel element plus depth of box (volume element)

Question 2

Advanced Imaging Modalities: CT: reformatting MPR (multi planar reformatting)

Answer 2

allows views of data from sagittal, coronal or 3D orientations. Qualtiy is less than axial (pizel) data unless scanner can produce ISOTROPIC VOXEL (has same depth, width and height)

Question 3

Advanced Imaging Modalities: CT: Hounsfield Units (HU)

Answer 3

used to describe shade of gray that tissue presents on scan - range is -1000 to +3072 HU.
Specific Tissue HU’s =
WATER = 0

Question 4

Advanced Imaging Modalities: CT: artifacts

Answer 4

phenomenon = one part of detector cannt distinguish bw diff tissues called partial volume effect

Question 5

Advanced Imaging Modalities: MRI: image characteristics: T1 weighted images:

Answer 5

fat = BRIGHT
cord higher signal than CSF
medullary bone and SC = higher signal
water and cortical bone lower

Question 6

Advanced Imaging Modalities: MRI: image characteristics: T2 weighted images:

Answer 6

Water and edema = BRIGHT
CSF higher than cord
less precise detail
nucleus pulposis = BRIGHT
Fat = loses signal compared to T1
cortical bone is DARK

Question 7

Advanced Imaging Modalities: MRI: image characteristics: signal intensity

Answer 7

how diff structures described as opposite to density as used with CT.
high signal = bright/light/white on image
low signal = dark/black on image
intermediate = anywhere inbetween

Question 8

Advanced Imaging Modalities: MRI: image characteristics: contraindications to MRI

Answer 8

anything with batteries or iron, any pt who can’t hold still ei seizures…
cardiac pacemaker, implanted cardiac defibrillator, aneurysm clips, carotid artery vascular clamp, neurostimulator, insulin or infusion pump, implanted drug infusion device, bone growht.fusion stimulator, cochlear, otologic or ear implant, some tattoos

Question 9

CT VS. MRI:CT uses xrays (ionizing radiation);

Answer 9

CT uses xrays (ionizing radiation); MRI = radiofrquency and magnets

Question 10

CT VS. MRI: CT refers to densities in tissue

Answer 10

MR refers to signal intesnity

Question 11

CT VS. MRI: CT provides exemplary detial

Answer 11

MRI provides expemplary tissue differentiation

Question 12

CT VS. MRI: CT can be reformatted from axial data

Answer 12

MRI requires multiplanar image acquisition

Question 13

CT VS. MRI: CT is very fast

Answer 13

MRI slow

Question 14

CT VS. MRI: CT done on pts with metal/battery implants

Answer 14

MRI only with no batteries or ferrous metal in patient

Question 15

CT VS. MRI: CT done on unstable patients

Answer 15

MRI harder to use with unstable patients