Intro to Imaging Flashcards
X-rays (photons) from the tungsten target pass through the body to expose the…
Recording plate
In X-rays, the greater the attenuation or absorption of the photons by tissues, the (WHITER/DARKER) the density will appear.
Whiter
***Organs with air appear dark, bone appears white, and soft tissues and water have intermediate density.
How does the position of the patient influence the recorded image of an X-ray?
It depends on what you’re trying to get an image of. For example, the heart lies more anteriorly so we would want the recording plate to be anterior as well and take a Posteroanterior view. If it was posterior, and we recorded the image in Anteroposterior view then we can get a false magnification of certain things. In this case, the heart looks enlarged.
***For the kidneys, we would want an Anteroposterior view because they lie more posteriorly!
This is the term for a continuous stream of X-rays to view the movement of structure in real time.
Fluoroscopy
In Fluoroscopy, the X-ray source is (ABOVE/BELOW) the patient and an image intensifier and data capture equipment are (ABOVE/BELOW) the patient.
Below
Above
In Fluoroscopy, how is the whole apparatus able to be rotated to give 3D information?
With the C-arm
What can Fluoroscopy be used for?
- Barium contrast studies of GI tract
- Angiographic studies
- Catheter and tube placement
- Fracture repair and apparatus placement in ortho sx
In Fluoroscopy, X-ray images are taken at _______ frames per second for peripheral vascular studies and _______ frames per second for coronary artery studies.
2-3
15-30
This is a form of fluoroscopy that takes a rapid series of X-rays viewed in real-time. An image taken before contrast injection is used to digitally “subtract” bones and other tissues from the view after contrast is administered. This allows for better imaging of the vessels.
Digital Subtraction Angiography (DSA)
What can DSA be used for?
- Balloon angioplasty
- Stent placement
- Guide catheter placement
What is a downside of DSA?
It’s an invasive procedure (percutaneously gain access vasculature via artery)
In contrast to a DSA, these two procedures are relatively noninvasive and only require introduction of an intravenous catheter in an arm vein for contrast injection.
CTA (Computed Tomography Angiography)
MRA (Magnetic Resonance Angiography)
***MRA downside – takes a long time
Explain how Computed Tomography works?
Images are generated with X-rays passing through the body in a helical fashion as the patient moves through 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 axial (transverse) 3D images of body.
T/F. For CT, images in the sagittal and coronal planes can be reconstructed on the computer from the axial (transverse) images.
True
For CT, the gray-scale image can be manipulated on the monitor, allowing you to do what?
Enhance certain structures you want to see
CT density numbers are attenuation units measured by what scale (named after British dude)?
Hounsfield Scale
The number on the Hounsfield Scale set to middle gray is referred to as the _______ _______, and the range of the gray scale mapped onto the Hounsfield Scale is called the _______ _______.
Window level
Window width
All CT numbers below the window width display as (WHITE/BLACK). CT numbers above the window width display as (WHITE/BLACK).
Black
White
A wide window width is good for imaging _______, while a narrow window width is better for _______ _______ because it has a higher contrast.
Bone
Soft tissue
What are the advantages of using CT?
- Quick (a few seconds for whole body)
- Motion not really a problem
- Gray scale can be manipulated on screen
- Resolution excellent for many areas
- Widely available and cheaper than MRI
What are disadvantages of using CT?
- Uses ionizing radiation
- Renal function must be evaluated if contrast used
- Some patients allergic to iodine contrast
What is the main benefit of MRI over CT?
Does NOT use ionizing radiation
Briefly explain how an MRI works.
A big magnet aligns atoms (nuclear spin), then the atoms are knocked out of whack. As the atoms relax back into alignment, they leave a different gray scale that can be used to identify the different tissues.
This type of weighted MR measures the time taken for spinning protons to realign with the external magnetic field. Fluid (i.e., CSF) is dark in these images.
T1 (Longitudinal relaxation time)
This type of weighted MR measures the time taken for spinning protons to lose phase coherence among the nuclei spinning perpendicular to the main field. Fluid (i.e., CSF) is light in these images.
T2 (Transverse relaxation time)
What are the advantages of using MRI?
- No ionizing radiation
- Better soft tissue contrast than CT
- Extremely versatile (variety of pulse sequences can be used to visualize specific tissues and pathology)
What are disadvantages of using MRI?
- Longer time
- More expensive
- Images cannot be manipulated onscreen
- Tube narrower for patients (bad for claustrophobia)
- No metal in patient’s bodies
- Contrast can’t be used in pregnant women
- Patients with renal dysfunction have higher risk of NSF
- Noisy
This type of imaging measures physiological activity rather than anatomy.
Nuclear medicine imaging
Explain how nuclear medicine imagining works.
Radioactive molecules are attached to other compounds to form radiopharmaceuticals that are administered orally or intravenously. These then bind to and/or are uptake by specific cells in specific organs and their radioactivity is recorded by an external gamma camera.
In nuclear medicine imagine, pathology can be detected by identifying focal areas of increased activity, known as ______ ______, or decreased activity which are called _______ _______.
Hot spots
Cold spots
This is a noninvasive imaging technique based on “pulse-echo” sound wave energy.
Ultrasound
Explain how an ultrasound works.
A transducers moving over the skin emits pulses of sound waves into the body and then functions as a receiver that records the energy from the “echo” or reflection of sound waves from tissue interfaces within the body.
With ultrasound, a computer interprets the sound waves as real-time images. What are high-frequency transducers (7-15 MHz) used to visualize?
Structures near the surface – i.e., neck vessels, thyroid glands, breasts, and testes
With ultrasound, a computer interprets the sound waves as real-time images. Lower-frequency sound waves (1-3.5 MHz) have greater penetrating power but less resolution and are used for imagining what structures?
Deep structures – i.e., abdomen and pelvis
Why are tissues deep to bone and air difficult to visualize with ultrasound?
Because bone absorbs mot of the sound energy and air reflects most of it.
What type of ultrasound measures blood flow?
Doppler ultrasound
What are the advantages of using ultrasound?
- Portable
- Inexpensive
- No ionizing radiation
- Good at capturing motion
