Introduction to Medical Imaging

Question 1

how does x-ray work?

Answer 1

x-rays (photons) from the tungsten pass through the body to expose the recording plate the greater attentuation or absorption of the photons by tissues, the whiter the density will appear organs with air will appear dark, bone will appear white. soft tissues and water have an intermediate density greater thickness of bone or soft tissues results in white density

Question 2

want what is imaging for x-ray, closest or farther away to to recording plate

Answer 2

closest

Question 3

how does fluoroscopy work

Answer 3

uses a continuous stream of x-rays to view the movement of structures in real-time, the x-ray source is below the patient, an image intensifier and data capture equipment are above the patient, with a C-arm, the whole apparatus can be rotated to give 3D information essentially rotate the C-arm, which produces the x-rays and records them

Question 4

what does fluoroscopy used for

Answer 4

barium contrast studies of the GI tract, a variety of the angiographic studies, catheter and tube placement, fracture repair and apparatus placement in orthopedic surgery, and many other procedures

Question 5

what did digital subtraction angiography replace

Answer 5

traditional technique of taking an x-ray after injecting the circulation of interest with contrast

Question 6

DSA is a form of fluouroscopy, image taken before contrast injection, then what

Answer 6

image taken before is used to digitally subtract bones and other tissues form the view after contrast is performed, allowing better imaging of the vessels

Question 7

what can DSA be used for

Answer 7

can be used for diagnostic purposes and therapeutic treatment, angioplasty and stent placement, and guide catheter placement

Question 8

downside of DSA

Answer 8

invasive procedure in which artery must be entered percutaneously, CTA and MRA are relatively noninvasive procedures that only require an introduction of IV catheter in an arm vein for contrast injection

Question 9

what is computed topography

Answer 9

x-rays in a donut, current multidetector with x-rays passing through the body in a helical fashion as the patient moves through a gantry containing a rotating x-ray tube detectors on the opposite side of the tube collect the x-rays that have passed through the body mathematical algorithms reconstruct transverse planes sagittal and coronal planes and 3D renderings can be reconstructed from computer gray-scale image can be reconstructed by monitor

Question 10

what is the hounsfield scale

Answer 10

computed density umbers are attentuation units

Question 11

on hounsfield scale, water, air, and compact bone

Answer 11

water is zero, air is -1000, compact bone is +3095 most soft tissues in the body have CT numbers between -100 and +100

Question 12

wide window width is good for what

Answer 12

imaging bone

Question 13

narrow window

Answer 13

better for soft tissfue

Question 14

number on the Hounsfield scale set to middle gray is what

Answer 14

window level

Question 15

range of the gray scale is what

Answer 15

window width

Question 16

all CT numbers below the window width are what

Answer 16

black

Question 17

all CT numbers above the window width are what

Answer 17

white

Question 18

advantages of CT

Answer 18

quick, motion not as much of a problem, gray scale can be manipulated on the screen, resolution excellent for many areas, widely available and cheaper than MRI

Question 19

disadvantages of CT

Answer 19

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

Question 20

how does MRI work

Answer 20

huge magnet, align atoms, hit tissues with radiofrequency and get it off alignment, then allow realignment, but atoms go back to equilibrium at different rates, creating gray scales

Question 21

advantages of MRI

Answer 21

no ionizing radiation, better soft tissue contrast than CT, extremely versatile, a variety of pulse sequences can be used for visualizing specific tissues and patholoy

Question 22

disadvantages of MRI

Answer 22

longer time for sequences (many minutes), more expensive, images cannot be manipulated like in CT (parameters have to be set before scan) gantry narrower than in CT (worse for claustrophobic patients) patients cannot have metal in the body gadolinium contrast cannot be used in pregnant women patients with renal dysfunction have increased risk of NSF (nephrogenic systemic fibrosis) noisy

Question 23

atoms return to equilibrium at different times, creating?

Answer 23

radiofrequency energy emitted by the protons during this relaxation time can be measured by the current generated in the receiver coil

Question 24

different issues have different relaxation times, why?

Answer 24

tissues have different relaxation times, depending on water content and general molecular composition

Question 25

what is T1

Answer 25

longitudinal relaxation time, measure of time for spinning protons to realign with the external magnetic field, CSF is dark in T1 weighted images

Question 26

what is T2

Answer 26

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 (such as CSF) is light)

Question 27

CT vs. MR

Answer 27

study of blood vessels and other structures with CT and MRI involves computer reconstruction of 3D images volume-rendering algorithms that reproduce depth perspective or maximum intensity projection that superimpose vessels on each other

Question 28

what is nuclear medicine?

Answer 28

measures physiological activity, not anatomy radioactive molecules are attached to other compounds to form pharmaceuticals that are administered orally or intravenously activity measured by external gamma camera patholoy can be identified by focal areas of increased activity such as hot spots and cold spots

Question 29

what is ultrasound

Answer 29

non-invasive techniques, whether transducer emits pulses of sound waves into the body, then functions as a receiver that records the energy from the echo or reflection of sound waves from tissue interfaces within the body

Question 30

high-frequency (7 to 15 MHz)

Answer 30

use to visualize structures such as thyroid gland, breasts, and testes

Question 31

lower-frequency sound waves

Answer 31

greater penetrating power but less resolution, used for deeper structures in the abdomen and pelvis

Question 32

ultrasound advantages

Answer 32

cheaper, no ionizing radiation, good at capturing motion, portable

Question 33

lower-frequency sound waves (1 to 3.5 MHz)

Answer 33

greater penetrating power but less resolution, used for deeper structures in the abdomen and pelvis