Thoracic imaging Flashcards
What is the optimal position for frontal and lateral views
anterior chest against the detector for the frontal view and the left chest against detector for the lateral view. This minimizes the heart shadow because the heart is closer to the detector.
X-ray attenuation measurement unit
Hounsfield units
Describe X-ray attenuation
Water is used as a reference point for x-ray attenuation and measures 0 HU. Fat attenuates fewer x-rays at -20 to -50HFU . Air attenuates the least x-rays at -1000 HU. Soft tissues attenuate more x-rays than water and will measure in the 30 to 50 HU. Calcium/bone attenuate more x-rays in the range of 700 up to 3000 HU and metal attenuates the most with HU’s greater than 2000
What is windowing
Adjusting grey-scale relative to measured radiodensity for a specific structure (ie. Lungs, bones, etc).
American college of radiology Appropriateness criteria
An online guide for the clinician and radiologist to insure that the best imaging is selected for the clinical situation. Specifies imaging for clinical indications, radiation risks, contraindications, etc.
High resolution vs standard chest CT
Standard: 3-5mm slice thickness images taken while supine and inspiration. High resolution: <3mm slice thickness images taken in supine inspiration, supine expiration and prone inspiration. Different acquisitions allow for evaluating specific findings such as air trapping on expiratory images and posterior pulm fibrosis on prone images.
Which CT method is preferred for diseases of small airways (bronchioles) or pulmonary fibrosis
high resolution chest CT
How is CT angiogram performed?
A bolus of iodinated IV contrast is injected into a peripheral vein, then the image is taken based upon the structure of interest. Pulmonary arteries are imaged 10-20seconds after bolus, coronary arteries 15-25 seconds after bolus.
What is nuclear scintigraphy
aka nuclear medicine/imaging: patient is administered a radioactive substance (radiotracer) that then undergoes nuclear decay and emits gamma radiation that is then absorbed by a detector (gamma camera) to produce an image.
How is nuclear scintigraphy used for chest imaging
cardiac perfusion imaging and pulmonary ventilation perfusion scans
What are pulmonary VQ scans
type of nuclear medicine: upright patient inhales aerosolized technetium or xenon 133 with the gamma camera positioned next to the chest to produce a single posterior projection or multiple projections of the chest. Then to measure perfusion, patient is given IV macro-aggregated albumin with technetium to show the distribution of pulmonary perfusion.
How is cardiac perfusion measured
nuclear medicine: Stress and rest imaging of heart after IV administration of technetium radiotracer. The gamma camera is rotated around the chest to get planar images in desired cardiac planes
