Diagnostic Imaging for NM Disorders Flashcards
What are the routine radiographic projections? What are the special radiographic projections?
Routine: AP, PA, lateral, oblique
Special: sunrise, open mouth
The more dense of a tissue, the more OR less x-rays penetrate the tissue to expose the film.
Less
The more dense an object, the greater OR lesser absorption of x-rays.
Greater
For radiolucent structures, is the density low or high; exposure low or high? Will the structures appear dark or bright?
What would it be for radiopaque structures?
Radiolucent: low density and high exposure of film, so they will turn out dark,
Radiopaque: high density and low exposure of film, so they will turn out bright.
What is pneumoencephalography?
X-ray imaging following injection of air into subarachnoid space to displace CSF and improve signal contrast; helps to visualize ventricular anomalies.
What is cerebral angiography?
X-ray imaging of the blood vessels of the brain following injection of a contrast agent; helps to identify vascular anomalies and occlusions.
What is myelography?
X-ray imaging following injection of contrast into CSF to improve contrast/imaging in vertebral column/spinal cord, subarachnoid space, nerve roots.
How do CTs work?
It uses x-ray beam and a row of detectors on opposite sides of the head. The detector rotates around the head, and the patient is moved through the scanner, process is repeated. You can either have a single slice or spiral multidetector CT.
What are the three types of density on CT scans? How do they appear?
Hyperdense: dense structures (bone, calcifications); white
Hypodense: less dense structures (air); black
Isodense: intermediate density structures (brain tissue); gray
Discuss the density of a fresh hemorrhage, after 1-2 weeks, and after 2-3 weeks, as they appear on a CT.
Fresh hemorrhage is white.
1-2 weeks: the clot is broken down and appears isodense with brain tissue.
2-3 weeks: the area of hemorrhage will appear hypodense.
Describe CT with intravenous contrast.
Iodine is injected, it is denser than the brain. Areas that have increased vascularity or breakdown of the blood-brain barrier appear hyperdense (white).
Why would you not want to use CT with intravenous contrast if you suspect intracranial hemorrhage?
It is harder to distinguish that there is actually a bleed with contrast.
What is the window width? Window level?
Window width: range of radiodensities (HU) displayed on an image.
Window level: central density (HU) displayed on an image.
How does an MRI work?
Uses magnetic energy and radio-frequency pulses to generate images.
What happens to the protons when the radiofrequency pulse is applied at right angles to magnetization for MRI? What happens when the radiofrequency pulse stops?
The protons experience altered alignment, some flip into a higher energy state, when the pulse is applied. The protons realign with magnetic field, energy absorbed while out of alignment is released, when the pulse stops.
What three things determine the intensity of MRI signal?
- Proton density
- T1 (longitudinal) proton relaxation times - net direction of spins
- T2 (transverse) proton relaxation times - depends on the net coherence of precessions.
Regarding MRIs, what is time to echo? Time to repetition?
Time to echo: time at which the signal is captured.
Time to repetition: time at which the radiofrequency pulse is repeated to again displace the protons.
What is the difference between a T1 and T2-weight image for MRI?
T1-weighted: tissues that rapidly release energy are brighter (fat); tissues slow to release energy are darker (water); assessing the anatomy.
T2-weighted: tissues that rapidly release energy are dark (fat); tissues slow to release energy are brighter (water); assessing abnormal fluid.
MRI appearance of chronic ( > 14 days) intracerebral hemorrhage for T1 and T2 weighted images.
T1: darker gray outer rim
T2: black outer rim
What imaging is considered Neuroangiography?
Doppler Ultrasound, CT Angiography. and MRA
What is Neuroangiography?
Non-invasive procedures to visualize blood vessels.
What is the gold standard to visualize blood vessels?
Invasive Angiography
If you wanted to view arterial stenosis, what type of Neuroangiography would you use?
Doppler Ultrasound
If you wanted to look at the blood supply to the brain or spinal cord, what type of Neuroangiography would you use?
CT Angiography
