Imaging of the Lung I & II

Question 1

Primary imaging modalities for chest evaluation

Answer 1

• CXR
• CT (computed tomography)
• nuclear scintigraphy
• MRI (magnetic resonance imaging)
• Echocardiography
• ultrasound

Question 2

CXR technique

Answer 2

• 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
• 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.

Question 3

CT technique

Answer 3

• image produced by passing patient between rotating xray beams and detectors
• produces volumetric data ==> anatomic planar images (usually axial)

Question 4

Advantages of CT

Answer 4

• 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)

Question 5

HRCT and indications

Answer 5

• 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

Question 6

Imagining of vasculature technique

Answer 6

• CT w/IV contrast
• contrast into peripheral vein and time CT imaging with target vasculature (e.g. pulmonary arteries vs. coronary arteries/aorta)

Question 7

Nuclear Scintigraphy characteristics

Answer 7

• pt administered a radioactive substance (radiotracer) ==> emits gamma radiation ==> absorbed by detector ==> image
• used in pulmonary VQ scans
• common radionuclide = technetium 99m

Question 8

VQ scan technique

Answer 8

• 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

Question 9

MRI technique

Answer 9

• 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

Question 10

Value of portable chest radiograph

Answer 10

• detect correct/incorrectly positioned central catheters
• study supports of regular ICU portable chest radiographs to guide pt care

Question 11

Imaging used to dx pulmonary embolism

Answer 11

• CT pulmonary angiogram
• easy/fast availability
• binary diagnosis of pulmonary embolism
• demonstrates alternative diagnoses
• provides prognostic information

Question 12

Major radiographic findings of cardiogenic pulmonary edema

Answer 12

• cardiomegaly
• vascular redistribution
• interstitial opacities (Kerley B lines)
• consolidation
• pleural effusions

Question 13

Classic imaging finding in pneumonia

Answer 13

• silhouette sign: in the setting of community-acquired pneumonia
• The silhouette sign is a fundamental concept in radiography where objects of equal density lose their differentiating borders when placed in contact with each other
• The term “Consolidation” will also be discussed to include the major substances that can fill the alveoli in the setting of consolidation.