Introduction to Medical Imaging Flashcards
how does x-ray work?
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
want what is imaging for x-ray, closest or farther away to to recording plate
closest
how does fluoroscopy work
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
what does fluoroscopy used for
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
what did digital subtraction angiography replace
traditional technique of taking an x-ray after injecting the circulation of interest with contrast
DSA is a form of fluouroscopy, image taken before contrast injection, then what
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
what can DSA be used for
can be used for diagnostic purposes and therapeutic treatment, angioplasty and stent placement, and guide catheter placement
downside of DSA
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
what is computed topography
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
what is the hounsfield scale
computed density umbers are attentuation units
on hounsfield scale, water, air, and compact bone
water is zero, air is -1000, compact bone is +3095 most soft tissues in the body have CT numbers between -100 and +100
wide window width is good for what
imaging bone
narrow window
better for soft tissfue
number on the Hounsfield scale set to middle gray is what
window level
range of the gray scale is what
window width
all CT numbers below the window width are what
black
all CT numbers above the window width are what
white
advantages of CT
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
disadvantages of CT
uses ionizing radiation, renal function must be evaluated if contrast used, some patients are allergic to iodine contrast
how does MRI work
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
advantages of MRI
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
disadvantages of MRI
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
atoms return to equilibrium at different times, creating?
radiofrequency energy emitted by the protons during this relaxation time can be measured by the current generated in the receiver coil
different issues have different relaxation times, why?
tissues have different relaxation times, depending on water content and general molecular composition
what is T1
longitudinal relaxation time, measure of time for spinning protons to realign with the external magnetic field, CSF is dark in T1 weighted images
what is T2
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)
CT vs. MR
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
what is nuclear medicine?
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
what is ultrasound
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
high-frequency (7 to 15 MHz)
use to visualize structures such as thyroid gland, breasts, and testes
lower-frequency sound waves
greater penetrating power but less resolution, used for deeper structures in the abdomen and pelvis
ultrasound advantages
cheaper, no ionizing radiation, good at capturing motion, portable
lower-frequency sound waves (1 to 3.5 MHz)
greater penetrating power but less resolution, used for deeper structures in the abdomen and pelvis
