Article Review (2): Emerging Clinical Applications of CT

Paper: Liguori C, Frauenfelder G, Massaroni C et al. Emerging Clinical Applications of Computed Tomography. Medical Devices: Evidence and Research 2015; 8: 265-278.

Article summary written by David Liaguno for discussion on 10/12/17:

The article “Emerging Clinical Applications of Computed Tomography” covers a brief history of X-rays and the basic physics of computer tomography (CT) scans. It then continues on to describe a few iterations of the CT scan and multi-detector CT (MDCT) and dual-energy CT (DECT) as well as their clinical applications. Lastly, the article describes several future prospects for CT scanning.

Multi-detector CT (MDCT) uses a two-dimensional array of detectors instead of a linear array.  This allows for the scanner to take multiple slices simultaneously. This greatly increases the speed of the image acquisition process. However, Images obtained from MDCT does not provide material–specific information because the representation of structures on the images depends solely on the linear attenuation coefficient of the constituent materials.

(Above) Dual-energy CT (DECT or spectral imaging) relies on the basic principle of obtaining two datasets with different kVp values from the same anatomical region. Usually 80 and 140kVp is used however for certain scenarios 100 and 140kVp may be used. X-ray attenuation of materials in the diagnostic energy
range varies according to the specific organ composition and the X-ray beam energy. Therefore, different substances show different CT numbers at the different energy levels. Increases in photon energy results in small decrease in CT value for materials of low atomic number while they cause a rapid decrease for materials with a high atomic number. Consequently, different materials with almost similar
coefficient attenuation values at different energy levels can be distinguished by DECT. Post Processing of DECT mainly uses three algorithms: the first optimizes images; the second identifies or differentiates certain materials; and the third quantifies a substance in the dataset.

Future prospects for CT are CT thermometry and CT-guided procedures. CT thermometry aims to monitor temperature of tissue during hyperthermal procedures. The technique is based on the dependency of the attenuation coefficient, and consequently the CT number, on temperature. This dependency is a result of thermal expansion. CT-guided procedures would allow for visualization of internal procedure through noninvasive means. Hybrid PET-CT which combines functional and structural imaging is also an up and coming technology. Photon counting technology, which records every single photon, aims to reduce overall dose to the patient. Phase contrast imaging also aims to reduce overall dose to the patient.

 

One thought on “Article Review (2): Emerging Clinical Applications of CT

  1. Post-discussion summary

    We first discussed the variety of different types of CT scan types from the linear detectors to multi-detector CT scanners (MDCT) and dual-energy CT scanners (DECT). MDCT used two-dimensional arrays of detectors to gather more data more quickly than linear detector arrays. DECT use two different X-ray energies simultaneously to be able to create a contrast between different materials with similar attenuation coefficients.

    We then continued on into how these different types of CT could possibly reduce radiation dosage to the patient. Additionally we established how helical CT scanners are predominantly used in current day medical situations because it allows for continuous movement of the patient through the scanning gantry. The helical scan data is then interpolated to gain full slice information to fully process a three-dimensional image.

    Another large part of the discussion was about the future applications of CT technology. For example how CT could be used for thermometry because attenuation is density dependent and tissues responds to thermal expansion. Or how photon counting and phase contrast imaging can be used as possible ways to lower the dosage to patients in the future. We also discussed the use of CT for CT guided procedures. CT scans can be used to see where a medical device is inside of a patient. This helps allow the surgeon to perform the surgery with greater accuracy, but it takes time because every time an image needs to be taken the surgeon must leave the room so as not to be effected by scattered X-rays.

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