BODY CT PROTOCOL DESIGN

Radiation modulation in body MDCT Body CT scans are the primary contributor to patient radiation exposure because of the widespread utilization of this imaging modality and the radiation delivered relative to other imaging modalities. Various innovations in MDCT (multidetector CT) data acquisition technology have been implemented to decrease the administered radiation dose. These include the following:
•     Z axis coverage: careful selection of the scan start and end points, elimination of pelvic CT if not necessary for abdominal imaging
•     Tube current modulation: a low tube current can be selected in smaller patients depending on weight. Alternatively, tube current can be modified based on the patient's body habitus based during each rotation (AP vs transverse) or depending on anatomic level (cranial vs caudal circumference and tissue components)
•     Use of a lower kVp: results in reduced radiation dose with increased attenuation of vascular structures because the kVp approaches the k-edge of iodine.
•     Tailoring the number of acquisitions: a very effective means of reducing radiation dose in abdominal CT.
Use of dose reduction measures is tempered by the goal of high image quality, which is inversely related to the noise resulting from low dose protocols. To address this challenge, manufacturers have revised a primary step in CT imaging: the process of reconstructing the raw data. Traditionally performed with by filtered back projection (FBP), only a portion of the raw data was incorporated into the reconstructed volume. Iterative reconstruction (IR) incorporates more of the original data to generate images with measurably reduced noise. Accordingly, using iterative reconstruction to increase the contrast-to-noise ratio enables radiation dose reduction.

 

References 1. Raman SP, Johnson PT, Deshmukh S, Mahesh M, Grant KL, Fishman EK. CT dose reduction applications: available tools on the latest generation of CT scanners. J Am Coll Radiol. 2013 Jan;10(1):37-41. doi: 10.1016/j.jacr.2012.06.025. Review. PubMed PMID: 23290672.

2. Johnson PT, Mahesh M, Fishman EK. Image Wisely and Choosing Wisely: Importance of Adult Body CT Protocol Design for Patient Safety, Exam Quality, and Diagnostic Efficacy. J Am Coll Radiol. 2015 Nov;12(11):1185-90.

3. Patino M, Fuentes JM, Singh S, Hahn PF, Sahani DV. Iterative Reconstruction Techniques in Abdominopelvic CT: Technical Concepts and Clinical Implementation. AJR Am J Roentgenol. 2015 Jul;205(1):W19-31.

 
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