Introduction to Medical Imaging

Question 1

in an X ray, what objects appear white vs dark

Answer 1

the greater the attenuation or absorption of the tissues, the whiter the density

organs with air appear dark

bone appears white depending on the thickness of bone

Question 2

How does the position of the patient influence the recorded imgae on an X ray

Answer 2

things can be magnified if they are are far from the lens and we focus on something close to the lens

thats why anything we want x rayed should be closest to the recording plate to eliminate any sort of magnification.

we can change a persons view by (AP or PA)

ie. if imaging someones heart, want PA view because heart is closest to the recording plate

Question 3

fluoroscopy

Answer 3

continuous stream of X ray that wraps around person with C arm to get 3D info

used for lots of surgeries like orthopedics and catheter and tube placements

Question 4

Digital subtraction (DS) angiography

Answer 4

form of fluoroscopy were you take an x ray after injecting the circulation of interest with contrast

Question 5

Digital subtraction (DS) angiography downside

Answer 5

is an invasive procedure in where an artery must be entered percutaneously

Question 6

Computed Tomography (CT)

Answer 6

x rays pass through the body and are collected in a helical fashion

use algorithms to create transverse plane, sagittal and coronal planes of viewing

Question 7

Hounsfield scale

Answer 7

it is the scale of grey and “resolution of the images” it adjusts the contrast of the “grey” coloring

window level= the middle grey
Window width= the range of grey scale around the level

below window width display as black
above window width display as white

Question 8

Hounsfield scale for soft tissue

Answer 8

narrow width to help increase the contrast between tissues

Question 9

Hounsfield scale for bone

Answer 9

want a wide width to pick up the imaging of the bone vs everything else

Question 10

Advantages of CT

Answer 10

quick, a few seconds for the whole body
motion not as much a problem
gray scale can be manipulated
resolution excellent for many areas
widely available and cheaper than MRI

Question 11

Disadvantages of CT

Answer 11

uses ionizing radiation
renal function must be evaluated if contrast is used
some patients are allergic to iodine contrast

Question 12

Magnetic Resonance Imaging (MRI)

Answer 12

images created using radio frequency energy emitted by hydrogen protons when strong magnetic fields generated around a patient are manipulated

Question 13

T1 MRI

Answer 13

Longitudinal relaxation time,
measure of the time taken for spinning protons to realign with the external magnetic field

fluid is dark

Question 14

T2 MRI

Answer 14

Transverse relaxation time
measure of the time taken for spinning protons to lose phase coherence among the nuclei spinning perpendicular to the main field

fluid is light

Question 15

Advantages of MRI

Answer 15

No ionizing radiation
very detailed soft tissue contrast than CT
Extremely versatile: a variety of pulse sequences can be used for visualizing specific tissues and pathology

Question 16

Disadvantages of MRI

Answer 16

Longer time for sequences: many minutes
more expensive
images cannot be manipulated on viewing screen like CT, parameters must be set before each scan
Gantry is narrower than CT, bad for claustrophobic patients
Patient cant have metal in body
Gadolinium contrast cant be used in pregnant woman
noisy
patients with renal dysfunction have increased riskof Nephrogenic systemic fibrosis

Question 17

Nuclear Medicine overview

Answer 17

measures physiological activity rather than anatomy
give patient radiopharmaceuticals that attach to specific cells or uptaked by them
pathology can be identified by increased activity like hot spots or decreased activity like cold spots

Question 18

Ultrasound overview

Answer 18

uses pulse echo sound wave energy to create images
high frequency (7 to 15 MHz) visualize structures near surface
low ffrequency (1-3.5 MHz) have deeper penetration power but poorer resolution, gets deeper structures abdomen and pelvis

Air is blcak
and bone reflects so assuming white

Question 19

Ultrasound advantages

Answer 19

Really low risk
fast important in trauma patients
portable
inexpensive
no ionizing radiation
good at capturing motion