Primary imaging modalities for chest evaluation
- CXR
- CT (computed tomography)
- nuclear scintigraphy
- MRI (magnetic resonance imaging)
- Echocardiography
- ultrasound
CXR technique
- x-rays from a focal point ==> radiographic detector
- pt casts shadow on detector = x-ray image
- shadows depend on: size, distance from light source to object, distance of light source to wall
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ideal positioning of the patient for standard two-view chest radiographs places their anterior chest against the detector for the frontal view and the left chest against detector for the lateral view.
ideal positioning of the patient for standard two-view chest radiographs places their anterior chest against the detector for the frontal view and the left chest against detector for the lateral view.
CT technique
- image produced by passing patient between rotating xray beams and detectors
- produces volumetric data ==> anatomic planar images (usually axial)
Advantages of CT
- mroe accurate depication of anatomic objects
- includes density of objects
- grey-scale can differentiate densisties of air, fat, fluid, soft tissue, bone/calcium, and metal
- caused by various levels of x-ray attenuation (measure in Hounsfield units (HU))
- water = 0 HU
- air (-1000 HU) < fat < water < soft tissue < calcium/bone < bone < metal (>2000 HU)
- caused by various levels of x-ray attenuation (measure in Hounsfield units (HU))
- water = 0 HU
- air (-1000 HU) < fat < water < soft tissue < calcium/bone < bone < metal (>2000 HU)
HRCT and indications
- High resolution Chest CT = axial slices < 3mm thick + images acquired @ supine inspiration, supine expiration and prone inspiration (vs. only supine inspiration in standard CT)
- Allows evaluation of: "air trapping" and subtle pulmonary fibrosis
- order if DDx includes: diseases of small airways (bronchioles) or pulmonary fibrosis
- order if DDx includes: diseases of small airways (bronchioles) or pulmonary fibrosis
Imagining of vasculature technique
- CT w/IV contrast
- contrast into peripheral vein and time CT imaging with target vasculature (e.g. pulmonary arteries vs. coronary arteries/aorta)
Nuclear Scintigraphy characteristics
- pt administered a radioactive substance (radiotracer) ==> emits gamma radiation ==> absorbed by detector ==> image
- used in pulmonary VQ scans
- common radionuclide = technetium 99m
VQ scan technique
- nuclear scintigraphy technique used
-
upright pt inhales aerosolized technetium or xenon 133 with the gamma camera positioned next to the chest ==> single posterior projection or multiple projections
-
perfusion measured via administered IV macro-aggregated albumin (MAA) with technetium the collects in the patient’s pulmonary capillaries and reflects the distribution of pulmonary perfusion
upright pt inhales aerosolized technetium or xenon 133 with the gamma camera positioned next to the chest ==> single posterior projection or multiple projections
perfusion measured via administered IV macro-aggregated albumin (MAA) with technetium the collects in the patient’s pulmonary capillaries and reflects the distribution of pulmonary perfusion
MRI technique
- Hydrogen atoms (plentiful within the water in body) create a magnetic field
- Place body within strong magnetic field ==> protons aligh ==> radiofrequency passed trhough and detected ==> image
Value of portable chest radiograph
- detect correct/incorrectly positioned central catheters
- study supports of regular ICU portable chest radiographs to guide pt care
Imaging used to dx pulmonary embolism
- CT pulmonary angiogram
- easy/fast availability
- binary diagnosis of pulmonary embolism
- demonstrates alternative diagnoses
- provides prognostic information
Major radiographic findings of cardiogenic pulmonary edema
- cardiomegaly
- vascular redistribution
- interstitial opacities (Kerley B lines)
- consolidation
- pleural effusions
Classic imaging finding in pneumonia
