CT, MRI, and Nuclear Imaging

Question 1

Briefly describe what CT-scans are and how they work

Answer 1

• What it is → X-ray beam and detector within circular scanner that moves around the patient
  
  • computer interprets (reconstructs) image
  • tissues assigned different shades of gray
  • series of cross-section slices (axial); can be reconstructed in sagittal and coronal planes, as well as 3D

Question 2

Give several example indications for CT-scans

Answer 2

1. Bone and soft tissue tumors
2. Fractures
3. Intra-articular abnormalities
4. Bone fragment detection
5. Bone mineral analysis (i.e. metabolic disorders)
6. Neuroimaging

Question 3

limitation(s) of CT-scans

Answer 3

inability to distinguish small areas of different tissues

Question 4

describe the scanning process in CT-scans

Answer 4

1. Scout image (2D) taken to localize target structures
2. Helical (spiraling) slices taken continuously with multiple-detector rows
   
   1. volumetric scanning possible with this, as structures can be made into 3D images

Question 5

describe the data conversion process in CT-scans

Answer 5

1. Radiodensities for each cubic millimeter
2. Converted from digital signals into matrix
   
   1. each cell (pixel) assigned shade of gray
3. Matrix transformed into an image
4. Contrasts and window modification

Question 6

list and describe 2 CT-scan variants

Answer 6

1. 3D CT
   
   1. multiplantar reconstruction → images can be rotated in space on a computer screen
2. CT Myelogram
   
   1. contrast material allows visualization of structures that impinge on neurologic structures
   2. distinguish osteophytes, ligaments infolding, and disc material

Question 7

when viewing CT-scans, denser structures appear _________

Answer 7

more white

Question 8

______is an advantage of CT-scans over radiograph

Answer 8

radiodensity free of superimposed tissues

Question 9

what is voxel?

Answer 9

product of pixel and slice thickness

average density of different tissues represented from within the voxel

Question 10

cross-sectional anatomy familiarity is important with CT-scans. List 3 different plane views and how to orient yourself with them

Answer 10

1. Axial image → as if the pt were supine, viewing looking in caudocephalad direction
2. Sagittal image → view form left to right
3. Coronal image → view as if facing the pt

Question 11

list CT-scan clinical applications pertaining to bone

Answer 11

1. subtle fracture
2. degenerative changes
3. serious trauma
4. spinal stenosis
5. IV disc pathology
6. Intra-articular loose bodies
7. Osseous alignment in any plane

Question 12

list CT-scan clinical applications for neuroimaging

Answer 12

1. Acute trauma (initial assessments)
2. SPECT
3. PET

Question 13

list benefits of CT-scans

Answer 13

1. less expensive than MR
2. less time than MR and US
3. benefits over problems related to physical barriers with MRI

Question 14

list limitations with CT-scans

Answer 14

1. given observation is based on radiodensity, tissues of similar radiodensity may not be distinguishable (e.g. tumors and surrounding soft tissues)
2. radiation exposure

Question 15

what is nuclear imaging?

Answer 15

imaging that uses radiopharmaceuticals (tracers) for the purpose of diagnosis, therapy, and research

can be used for static image or viewing over a period of time

Question 16

what is the general indication for nuclear imaging?

Answer 16

testing function of tissues

diagnosis by physiological change (as opposed to structure)

Question 17

describe the mechanism of nuclear imaging

Answer 17

1. radionuclide (emits gamma rays) introduced
2. absorbed differently by tissues based on metabolic activity
3. gamma rays observed by special camera
4. computer converts to digital image

Question 18

list and briefly describe the 6 different methods of nuclear imaging

Answer 18

1. Static → single image of targeted body region
2. Whole-body → AP (example: bone scans)
3. Dynamic → timed sequence
4. SPECT → 3D
5. PET → biologic function of cells
6. Combinations with CT and MR

Question 19

list indications for dynamic nuclear imaging

Answer 19

cardiac, hepatobiliary, gastric studies

Question 20

what does SPECT stand for?

Answer 20

Single Photon Emission Computed Tomography

Question 21

list indications for SPECT

Answer 21

bone, cardiac perfusion, brain, liver

Question 22

what does PET stand for?

Answer 22

Positron Emission Tomography

Question 23

list indications for PET

Answer 23

CNS studies, tumors

Question 24

list clinical indications for Nuclear Imaging

Answer 24

1. Cancer
   
   1. staging, observation, and testing response to therapeutic intervention
   2. screening pts with a high risk for metastasis to bone
2. Detection of metabolic bone diseases and other osteopathies
3. Detection of other bone abnormality

Question 25

list MSK indications for nuclear imaging

Answer 25

1. HO 2. fracture and stress fractures 3. inflammation/infection 4. complications of foreign hardware/prosthetic/medical device 5. CRPS 6. PFPS 7. AVN

Question 26

what is scintigraphy?

Answer 26

nuclear imaging of skeleton

Question 27

what is the function of scintigraphy and how do you interpret it's results?

Answer 27

function → confirm disease, ID extent of disease black spots (aka hot spots) on image typically indicate increased uptake

Question 28

what is a bone scan?

Answer 28

a nuclear imaging study of the skeleton comprised of 3 phases

Question 29

list the 3 phases of a bone scan

Answer 29

1. 1st phase → flow study (immediate) 2. 2nd phase → blood pool (30 minutes) 3. 3rd study → delayed (2-4 hours) imaging occurs over the few hours post injection

Question 30

list advantages/disadvantages of bone scans

Answer 30

1. Advantages 1. high sensitivity for changes in bone metabolism 2. Disadvantages 1. low specificity 2. poor anatomic detail

Question 31

list contraindications for bone scans

Answer 31

pregnancy currently breast-feeding

Question 32

list indications for MRI

Answer 32

1. soft tissue trauma 2. internal joint derangement 3. tumors

Question 33

list 2 variants of MRI scanners

Answer 33

open scanners upright scanners

Question 34

give a brief explanation of how MRIs work

Answer 34

1. MRIs measure the energy emitted by hydrogen nuclei as the respond to radiofrequency signals 2. energy differs by tissue 3. a radiofrequency wave pulse is applied at a right angle to align protons (hydrogen) in transverse plane which brings them to a higher energy state 4. as the protons realign with the magnetic field they release absorbed energy which creates a current that is induced in receiver coil 5. a contrast in image produced by different T1, T2 and # of hydrogen nuclei

Question 35

what does T1 and T2 mean?

Answer 35

technical terms that refer to the time taken between magnetic pulses and the image is taken

Question 36

describe T1 MRI

Answer 36

weighted images that measure energy from structures that give up energy quickly (like fat) good for anatomic detail tissues with higher water content appear darker

Question 37

describe T2 MRI

Answer 37

weighted images that measure energy from structures that give up energy slowly (like water) fat appears darker grainer, less spatial resolution good for ID of inflammation

Question 38

list several clinical applications for MRI

Answer 38

1. sensitive to changes in bone marrow → dx of bone tumor, stress frxs, AVN 2. Soft tissue injuries 1. ligament and tendon 2. meniscus 3. alternative to arthroscopic dx 4. disc pathology/neurologic impingement 3. Tumor staging 4. MR arthrography → arthrogram + MRI 5. MR Myelography → view spinal canal and subarachnoid space w/high resolution MRI + strong T2 weighing

Question 39

list limitations to MRI

Answer 39

1. imaging for bone 2. time for image 3. high cost/expensive 4. hardware can cause distortion of images 5. physical limitations with procedure parameters 1. ability to stay still 2. claustrophobic

Question 40

list contraindications to MRI

Answer 40

ferromagnetic metals (surgical clips, shrapnel)