PULMONARY INVESTIGATIONS-CT SCANS

SUMMARY

1. Conventional CT (cCT): require cables to wind and unwind, so they're slow & disadvantageous (e.g. respiratory misregistration and unreliable imaging of vascular structures due to timing issues). Used to visualize anatomy, but not evaluate the lungs.

2. High-resolution CT (HRCT): assesses lung parenchyma at high resolution as the x-rays are thinly collimated (restricting the beam to a given area), down to 5 acini surrounded by interlobular septa. Used for workup of solitary pulmonary nodules, emphysema, ILD & bronchiectasis.

3. Helical CT (hCT): works by shooting x-rays in a continuous helical rotation using slip rings instead of cables. Used to diagnose pulmonary embolism (CTPA uses hCT), MDCT is also replacing HRCT at some hospitals because it provides higher-resolution images of the pulmonary parenchyma.

4. Electron beam CT (ultrafast CT): initially developed for imaging of the heart. The x-ray source is swept electronically rather than mechanically, takes multiple images within the time of a single heart beat and uses less radiation than hCT. Used for evaluating congenital defects and pulmonary vasculature. Electron beam CT units are rare and cost double that of an hCT unit.

Reference(s)

Wilkinson, I., Furmedge, D. and Sinharay, R. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press. Get it on Amazon.
Feather, A., Randall, D. and Waterhouse, M. (2020). Kumar And Clark’s Clinical Medicine. 10th ed. S.L.: Elsevier Health Sciences. Get it on Amazon.
Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
Therapeutic Guidelines. Melbourne: Therapeutic Guidelines Limited. https://www.tg.org.au [Accessed 2021].