The Design principles and evidence used to construct the table of enhanced CT scan injection parameters.
The body weight distribution of our patient population was initially estimated by a chart review of 586 patients, and subsequently confirmed by recording body weights from 3992 consecutive CT scans. Between over 40% of patients undergoing CT scanning had breast cancer.
Weight categories were initially created with the intention that 90% of patients would be in the central 3 categories. It was subsequently shown that 88% of patients were in the central 3 categories, which is close enough. The intention was that the CT technologists would be able to memorize the scan parameters for the vast majority of patients, and only need to read the look-up table for patients who are outside the central 3 categories. This is what happens in actual practice.
Multiple successive versions of these tables were tried, and adjusted over time, to achieve optimum results. A brief description of these successive versions (series A,B,C,D,E,F,G,H and currently I) is described elsewhere.
The initial goal of the adjustments to the various series was to achieve uniform liver enhancement across all weight groups. By the middle of the study, this goal was achieved. The kidney enhancement pattern distribution and portal venous enhancement patterns were not significantly different across the weight groups (data not shown). About half-way through the study, it was realized that too-early scan Delays could cause insufficiently enhanced "hypodense" hepatic veins, which could be confused with metastases. Therefore, a goal of the later series protocol designs, was to gather data to enable a good estimate of an optimum compromise between liver enhancement and hepatic vein enhancement. Once this data was gathered and analysed, the final result, the series I "Cross Method" protocols were created. This represents a comprehensive analysis and justification of optimal parameters for portal-venous-phase spiral CT scanning.
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