Part III. Elements of good scan protocols: Building blocks of a good practice
There is no dearth of good scanning protocols on the web and in the journals, and yet one of my favorite place for a great protocol template lies in the public domain at the American Association of Physicists in Medicine website (http://www.aapm.org/pubs/CTProtocols/documents/AdultRoutineChestCT.pdf). The outstanding Working Group on Standardization of CT Nomenclature and Protocols has comprehensively described the nuances of a few common protocols for all major CT vendors. Even if one might not completely agree with the actual scan parameters, I find it hard to argue against the exquisitely structured protocols, which start at the level of clinical indication and then address patient positioning, contrast injection details, breathing instructions, and scan range. If you are in the business of making CT protocols, the site is a must visit!
In a good CT protocol, the header should state body region, protocol title, scanner details (name, vendor, slice profile) and version date. I am fond of stating to our technologists “With some luck I can fix noise and some artifacts, but I have no chance against chest CT compromised by motion artifacts.” This brings me to the amazing why, what, and how manual on respiratory instructions for CT of the lungs by Bankier and colleagues (1). For a chest CT, the best conversation a CT technologist can have with the patient pertains to breathing during scanning. No scan parameter is as important as clear, concise, correct breathing instructions for chest CT.
Once these crucial elements of scanning are addressed, you can then begin to populate specific scan parameters for planning radiographs (scout images), which serve several purposes beyond just planning the scan range. Parameters for transverse CT images should include specific values for scanning mode, kV, mA (or automatic exposure control descriptors), rotation time, detector configuration, table feed per rotation, pitch, reconstruction approach (filtered back projection or iterative reconstruction), reconstruction filter, field of view kernel or algorithm, section thickness, as well as section interval. Specifications for additional thin sections, coronal and sagittal multiplanar reformats and maximum intensity projection images should be clearly stated. We will discuss each of these items in separate blogs, I promise.
I personally prefer Excel, Spreadsheet or Worksheets to create and archive our protocols. Separate files are created for individual clinical indication based protocols. Each spreadsheet can have different pages or tabs for different CT scanners. I never use identical scan protocols for identical clinical indications for different CT scanner types. This ensures that one capitalizes upon individual strengths of different scanners.
1. BankierAA, O’Donnell CR, Boiselle PM. Respiratory instructions for CT examinations of the lungs: a hands-on guide. RadioGraphics 2008; 28: 919–931