Introduction to Medical Imaging Flashcards
How do X-Rays work?
Photons from tungsten target pass through body to expose the recording plate
X-Ray Rule:
Greater the absorption of photons by tissues, the …
Whiter the density will appear
On an x ray __ will appear white
Bones
On an x-ray ___ will have intermediate density
Soft tissues and water
The greater thickness of bone or soft tissue on an X-ray, the ___ density
Whiter
What is an AP Plain film radiograph?
What is closer to recording plate?
AP: Anteroposterior
goes from front to back
-back is closer to plate
So heart is farther away = enlarged
What is a PA Plain film radiograph?
What is closer to the recording plate?
PA: Posteroanterior
Goes from back to front
-front is closer to recording plate so heart is closer = normal size heart
If you want to keep an organ the right size, where would you put the plate?
Closer to the plate
I.e. Use AP view for kidneys
What is fluoroscopy?
Real time x-ray imaging
Shows movement of structure in real time
-has c arm so the whole apparatus can be rotated to give 3D info
When would you use fluoroscopy?
Is used for barium contrast studies of GI, variety of Angiographic, catheter and tube placement, fracture repair adn apparatus placement in ortho surgery
How many frames are taken per second for a peripheral vascular study using fluoroscopy?
2 to 3 frames/second
How many frames are taken per second for a coronary artery studies?
15-30 frames per second
What is Digital Subtraction Angiography (DSA)?
Form of fluoroscopy (real time x rays)
Tissues and structures not of interest = digitally subtracted
Allows for better imaging of vessels
What is DSA used for?
For diagnostics like balloon angioplasty, stent placement, guiding catheter placement
What is the downside of DSA?
Invasive bc artery must be entered percutaneously
(Unlike CTA and MRA which are relatively noninvasive procedures that only require IV catheter in arm vein for contrast injection)
What is an upside to DSA?
Quicker than an MR study
How does CT work? (Basic)
Patient slides thru a donut, x rays pass thru patient ina helical fashion and are detected on opposite side of tube
Algorithm reconstructs in 3D image
Grayscale image can be manipulated on monitor as well
What are the advantages and disadvantages to CT?
Quick, motion not a problem, gray scale can be manipulated, resolution excellent, widely available and cheaper than MRI
Disadvantages: uses ionizing radiation, must evaluate renal function if contrast used, allergy to iodine contrast
What is the hounsfield scale?
What is middle gray? Scale for middle gray?
What is window width
Scale for CT
Window level; -1000 to +3095
Range of gray so-called mapped onto housnfield scale
The narrower the width the ___ the contrast
Higher
If the CT is ABOVE the window width image will appear ____
White
If the CT is BELOW the window width, the image will appear ___
Black
you would use a narrow window width for __
Soft tissue
You would use a wide window width for __
Bone
What is the window level and width for Lungs?
Level = -550 Width = 1600
What is the window level and width for soft tissue?
Level = 70 Width = 450
What is the window level and width for bone?
level = 570 Width = 3077
If you wanted more contrast and not as much detail on a CT, what would you do to the width?
Make it narrower
will give more contrast and not as much detail
Does a MRI use Ionizing radiation?
No
How doe an MRI work?
Big magnet that atoms will align with
It will hit tissues with radio frequency so they all go out of alignment
Then relaxation time occurs where they all eat back into alignment
Depending on density of tissues, return to realignment will occur at a different rate
Different rate of return = different gray scale in image
What is the difference between T1 and T2 weighted MRIs?
How will fluid appear in each?
T1= longitudinal relaxation time = fluid is dark
T2 = transverse relaxation time = fluid is light
What are the advantages and disadvantages to MR?
Advantages: no ionizing radiation, better soft tissue contrast than CT, extremely versatile
Disadvantages: longer time for sequencing, more expensive, images cannot be manipulated on viewing screen, narrow matching (claustrophobia), no metal in body, no gadolinium contrast with pregnant women, increased risk for NSF in those with renal dysfunction, noisy
What will give more depth in an angiography study? CT or MR?
CT
What is nuclear medicine?
Radioactive molecules attached to other compounds to form radiopharmaceuticals.
Administered orally or intravenously
Designed to bind or be uptakes by specific cells in specific organs (esp. highly metabolic cells, i.e. CANCER)
Detector used to look at hot spots
What is one application of nuclear medicine?
look at breast cancer
What is an ultrasound?
A non invasive imaging technique using sound waves that echo back after being reflected from tissue interfaces within the body
When would you use a high frequency on an Ultrasound?
to visualize structures near the surface
I.e. neck vessels, thyroid gland, breasts, and testes
When would you use a low frequency on an Ultrasound?
Will have greater penetrating power, can image deeper structures in abdomen and pelvis
How does air show up on an ultrasound?
Black
What are the benefits to using ultrasound?
Low risk, portable, good for emergency situations, cheap
What is barium sulfate used to visualize as a contrast agent?
Hollow organs
I.e. for upper Gi study, colon study
What is iodine compounds used to visualize as a contrast agent?
Vessels (angiography)
I.e. for celiac arteriogram, hysterosalpingogram
What kinds of contrast agents does MR use?
Intravenous gadolinium oral agents (juice, H2O)
