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  • Described by the projection of the x-ray beam through the patient relative to anatomical position.
  • 2 views 90 degrees of each other are referred to as orthogonal views.
  • All x-rays should have side (right/left) markers.

2. Lung zones:

  • Upper zone: anterior aspect of upper 2 ribs.
  • Mid-zone: anterior aspect of ribs 2-4.
  • Lower zone: anterior aspect of rib 4 inferiorly.

3. Silhouettes:

  • Caused by differences in density- identify the site of the pathology by using silhouettes.
  • Can be caused by: cardiomediastinal, hilar, diaphragm, lesions.
  • What is obscured cannot be seen! Problem then lies behind whatever is obscuring it!
  • Note that if there is consolidation, you will gain the ability to see air-bronchograms whilst loosing the ability to see lung vessels.

4. Radiographic densities:

  • Density is directly proportional to attenuation. The more X-ray beams are attenuated, more dense is the material and the more opaque it becomes.
  • Opacities vs lucency: (DESCRIBES SOFT TISSUE PATHOLOGY) Opacity = white; lucency = black. Similar terminology: air space opacity = alveolar opacity = consolidation.
  • Veiling (diffuse) opacity can be caused by: (1) supine effusion (2) patient rotation (3) chest wall abnormalities (4) grid cutoff.
  • Grid-cutoff artifact: a grid is a filter. If the grid is not aligned appropriately you may get grid-cutoff artefacts.
  • Lucency can be focal or diffuse.
  • Sclerosis vs osteolysis: (DESCRIBES BONY PATHOLOGY) Sclerotic = increased bony mineralization + increased density. Lytic = decreased bony mineralization + decreased density.
  • Atelectasis = collapse of the whole lobe.

5. Cardiothoracic ratio (CTR):

  • Measured on a PA chest x-ray, and is the ratio of maximal horizontal cardiac diameter to maximal horizontal thoracic diameter (inner edge of ribs / edge of pleura).
  • A normal measurement should be ≤0.5.

6. Alveolar shadowing:

  • Pathological process that fills the alveoli.
  • When confluent, becomes consolidation.


1. Goodman, L. and Felson, B. (2015). Felson's principles of chest roentgenology. 3rd ed. Philadelphia, PA: Elsevier, Saunders.
2. Dähnert W. Radiology Review Manual. LWW. (2011) ISBN:1609139437. Read it at Google Books - Find it at Amazon
3. Elizabeth Puddy, Catherine Hill; Interpretation of the chest radiograph, Continuing Education in Anaesthesia Critical Care & Pain, Volume 7, Issue 3, 1 June 2007, Pages 71–75, https://doi.org/10.1093/bjaceaccp/mkm014

Ⓒ A. Manickam 2018

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