unit1.6 medical images

Question 1

Looking at an Xray/MRI they use specific frequencies of the electromagnetic spectrum. Explain how the spectrum is used in these imaging techniques

Answer 1

The idea is to subject the body to frequencies that allow you to see the desired tissue.

1. example
   
   1. bone is denser than most other tissues. X-rays are absorbed by dense materials, lead.
   2. When the body is bombarded with X-rays, the photons are at a frequency that is only absorbed by the bone. The skin and other tissue will not absorb the xrays, due to the electromagnetic frequency. making these tissues invisible

Question 2

What is the source in a CT? where on the EMR spectrum does computerized tomography take place?

Answer 2

CT uses specialized Xrays

1. Xrays
   
   1. are photons.
   2. released from source in every direction.

Question 3

explain terminology of CT, CAT and 3d xra

Answer 3

CT=CAT, computerized axial tomography

3D xray uses mathematicl tools to recreate a 3D structure from all the views of the body.

Question 4

what are the units of measurment in Xrays?

explain this photo with respect to how it is captured.

Answer 4

1. housnfield units: scale of radiodensity relative to water
   
   1. hu is porpotional to the density of the target

the photons that pass through the body strike the plate and generate a dark spot on the film. The lighter the spot on the film=denser the material.

Question 5

what can be used , in CT, to highlight structures of interest

Answer 5

1. radioopaque tracers(radiocontrast agents)
   
   1. agents
      
      1. radioactive isotopes
         
         1. iodine
         2. barrium
   2. introduces IV
   3. native contrast does not offer much differentiation of most tissue

Question 6

what type of scanning technology was used and what is used in the right photo compared to the left?

Answer 6

CT angiography

left is unehanced

right shows contrast enhancement of normal blood vessels and aberrant blood barrier, describing more features of the brain tumors blood supply.

Question 7

what was done to generate this photo

Answer 7

right is a digital subtractive angiography DSA

attained by imaging prior to injection and after injection, subtracting the former fromthe latter allows for a clearer photo of the blood supply

Question 8

list pros/cons of CT

Answer 8

1. pros
   
   1. rapid
   2. shows acute and subacute hemorrhages
   3. shows bone clearly
2. cons
   
   1. does not clearly show acute or subacute infarcts, ischemia or edema
   2. uses ionizing ration

Question 9

what frequency does an MRI operate at?

Answer 9

1. radio frequency pulse transmitted to the body
2. tissues protons align to an externally applied magnetic field
   
   1. exho is produced by the protons of the body that reveals the local chemical milieu

Question 10

explain the general understanding of using magnetic feild and what they act on.

Answer 10

In the natural state, protons are spinning in all directions. after long enough exposure to the magnetic field, they all go close to the same direction.

1. Bo aligns protons
2. T1 rate of alignment MFz
   
   1. protons precess at larmor freq, where values depend on Bo
3. B1 induce in-phase precession
4. T2 =the rate ofreduction of MFxy, and is independent of

When the magnetic feild is tured off, the protons lose the unidirectional spin state(decompose) going back to their original spin state.

A change in magnetic feild produces an electric feild, and visavera. When the protons change their direction they produce a repsonse, that is viewed as “echo.” The varying frequencies that the protons produce is received and constructed into an image.

Question 11

1. Explain the value of these two measurements

Answer 11

T1

1. value show the length of time for the protons the respond to the magnetic feild.
2. this value is dependent on the proton density
3. important characteristic of tissue, with different values for different tissues
4. growth of magnetization in Zaxis

T2

1. decay value measuring the dephasing of the protons. measures the spin-spin relaxation time
2. decay of magnetization in x/y axis

together these generate the equivelent of +/- like a film devopled. They allow structures to be enhanced.

Question 12

describe the general features of an MRI machine

Answer 12

magnets made of superconductors, operate at near 4.2K. allowing near zero resistance

1.5tesla magnetic feild allows a milimeter thickness of tissue to be examined. 3T would allow thiner slices.

Larmor frequency, 64MHz, is important in MRI. also called B1. This is the magnetic resonance of the proton. the protons are sent this signal and all align. After the RF is turned off/moved, the protons unilateral direction decays with respect to their chemical milieu.

Question 13

what agents can be used with MRI to view specific structures?

Answer 13

agents that are paramagnetic, very weakly attract by the poles of a magnet, but not retaining any permenant magnetism.

example

gadolinium

Question 14

list pros and cons of MRI

Answer 14

1. pros
   
   1. 3D
   2. good for soft tissue contrast
   3. no ionizing radiation
2. cons
   
   1. noisy
   2. claustrophibia
   3. expensive