Bayesian Analysis plus clinical example
pretest probability affects post-test probability. If you have a strong clinical suspicion of fracture but XR is negative, request further testing.
x ray attenuation: definition, function of what 3 variables?
X ray photons are “absorbed” by matter; amount of attenuation depends on: thickness, density of material (function of atomic number), and x ray beam kVp (peak kilovoltage/energy)
Xray: does an object of high density appear darker or brighter?
Brighter
X ray radiolucency: define
Allows x ray to pass through without absorption, penetrates most easily. Appears dark on XR
X ray radiodensity: define
Absorbs x ray beams, appears bright on XR
Name a highly radiolucent material
Air, fat
Name a material class with high radiodensity
heavy metal
Which is more radiolucent: bone or water?
water
Which is more radiolucent: contrast or bone?
Bone
Which is more radiodense: contrast or bone?
contrast
Which is more radiodense: bone or fat?
bone
PACS-define
Picture archiving and communication system-a medical imaging technology which provides economical storage of and convenient access to images from multiple modalities (source machine types).
DICOM-define
Digital Imaging and Communications in Medicine (DICOM) is a standard for handling, storing, printing, and transmitting information in medical imaging. It includes a file format definition and a network communications protocol.
RIS-define
A radiology information system (RIS) is a computerized database used by radiology departments to store, manipulate, and distribute patient radiological data and imagery. The system generally consists of patient tracking and scheduling, result reporting and image tracking capabilities.
HIS-define
A hospital information system (HIS) is an element of health informatics that focuses mainly on the administrational needs of hospitals
satisfaction of search
phenomenon in which the detection of one radiographic finding interferes with that of others; just because you found something doesn’t mean you found everything
Hounsfield Units: what modality of imaging? Define.
Measure of attenuation of x ray beam in CT scan
Hounsfield units: reference values for water and air
water=0, air=-1000
Hounsfeld units: bone, blood, muscle, fat
bone=1000, blood=40, muscle=10-40, fat=-50–100
CT scan: 4 types of artifact
Motion, metal, partial volume averaging, beam hardening artifact
CT scan motion artifact: example
Cardiac motion (less of an issue with today’s fast multislice scanners)
CT scan: Partial volume averaging artifact
More of an issue with thicker slices; a substance that occupies several voxels will get “averaged” and look larger and blurrier than it would if it was centered in 1 voxel
CT scan: metal artifact
Radiodense structures limits evaluation of adjacent structures, can be minimized by increasing kvp
CT scan: beam hardening artifact
Appears like an area of radiolucency (very dark area on scan), low energy portion of the spectrum filtered out,
CT contrast
Makes structures more radiodense, therefore brighter and easier to discern on scan. Administered orally, rectally, or intravenously.
CT contrast risks
allergic reactions (mild-rash; severe-HOTN, laryngeal swelling, CV collapse); renal failure (creatinine >1,5-1.8); contrast extravasation-contrast leaks out of a ruptured vessel
CT scan for pts on dialysis
IV CT contrast OK but not MRI contrast
CT scan advantages
fast, high resolution, can be reformatted after scan into 3D image in any plane (multiplanar reformatting MPR)
CT scan disadvantages
artifact, risks of IV contrast, RADIATION
ionizing radiation-define and risk
electromagnetic waves with the energy to knock an outer shell electron out of valence shell (creates an ion); can result in damage to DNA
ALARA
as low as reasonably achievable
radiation safety compromise
between dose and quality of image
Inverse Square Law of Radiation and Distance
radiation dose decreases as a function of the distance from the source squared
Linear No Threshold Model: assumption/stochastic effects
risk is directly proportional to the dose; sum of very small exposures have the same effect as one large exposure (e.g. 1 CT scan=100 XRs)
T1 Pulse sequence: behavior in water, fat
Dark in water, bright fat
T2 Pulse sequence: behavior in water, fat
Water and fat bright
PD pulse sequence: behavior in water, fat
Water intermediate, fat bright
STIR pulse sequence: behavior in water, fat
water bright, fat dark
MRI contrast: substance used, how administered
Gandolinium, intravenous contrast, bright on imaging
CT scan contrast:
Iodinated
Risks of gandolinium
Nephrogenic systemic fibrosis: occurs in pts with severe kidney failure or dialysis; EGFR 30-60 borderline, Gandolinium absolutely contraindicated EGFR <30
Gandolinium absolute contraindications
Pregnant women, pts with EGFR <30
MRI advantages
no ionizing radiation, lots of soft tissue information, sensitive to contrast, 3D data, can get angiogramswithout contrast, gandolinium not as allergenic
MRI disadvantages
long scan times, motion artifact, expensive, contraindications, claustrophobia
MRI safety: zones
Magnet is always on at full strength; zones: 1-public accessible; 2-supervised access, screening by MRI staff; 3-restricted area, prescreened pts and staff only; 4-magnet room
MRI dangers
missile effect, field interaction with medical devices, torque on implanted devices, acoustic noise, thermal effect from absorbed RF energy and induced currents, cryogens, gandolinium risks
MRI contraindications
pacemaker, nonremoveable cochlear implant, metal in the eye, noncompatible aneurysm clip, implanted electronic devices-insulin pumps, neurostimulator units, etc
MRI possible problems
metallic stents, previous projectile injury, penile implants, artificial limbs, tattoos, medication patches with metal, claustrophobia
Ultrasound benefits
cheap, no ionizing radiation, real time, good soft tissue detail, no artifact from metal, vascular imaging, good for MR incompatible patients
US drawbacks
limited penetration, operator dependent, doesn’t penetrate air or metal
US uses
rotator cuff integrity, baby hips, tendon integrity, joint effusions, guidance for interventional procedures
