CT perfusion in oncology: how to do it

Abstract

Robust technique and accurate data analysis are required for reliable computed tomography perfusion (CTp) imaging. Multislice CT is required for high temporal resolution scanning; 16-slice (or 64-slice) scanners are preferred for adequate volume coverage. After tumour localization, the volume of CTp imaging has to be positioned to include the maximum visible area of the tumour and an adequate arterial vessel. Dynamic scans at high temporal resolution (at least 1-s gantry rotation time) are performed to visualize the first pass of contrast agent within the tumour; repeated scans with low temporal resolution can be planned for late enhancement assessment. A short bolus of conventional iodinated contrast agent, preferably with high iodine concentration, is power injected at a high flow rate (>4 ml/s) in the antecubital vein. The breath-hold technique is required for CTp imaging of the chest and upper abdomen to avoid respiratory motion; free breathing is adequate for CTp imaging of the head, neck and pelvis. Using dedicated software, a region of interest (ROI) has to be placed in an adequate artery (as arterial input) to obtain density-time curves; according to different kinetic models, colour maps of different CTp parameters are generated and generally overlaid on CT images. Additional ROIs can be positioned in the tumour, and in all other parts of the CTp volume, to obtain the values of the CTp parameters within the ROI.

Figure 1

Density–time curve obtained by placing an ROI over the selected arterial input, plotting density (expressed in Hounsfield units (HU)) on the Y-axis and time (expressed in milliseconds) on the X-axis.

Figure 2

Selection of the end of the first pass. (A) Correct selection of the end of the first pass by choosing the lowest point after the peak of the density–time curve. (B) Early selection of the end of the first pass (one image too early) on the density–time curve. This resulted in an erroneous calculation of the perfusion parameters (BF, BV, MTT, PS). (C) Late selection of the end of the first pass (one image too late) on the density–time curve. This resulted in an erroneous calculation of the perfusion parameters (BF, BV, MTT, PS).

Figure 3

A 61-year-old patient with a squamous cell carcinoma of the left oropharynx. Colour maps for BF, BV, MTT and PS automatically generated by software, in which every pixel is assigned a colour that represents a numeric value for the perfusion parameter calculated for that voxel. High numeric values are represented by colour shades of yellow and red, and low numeric values are represented by colour shades of green and blue. (A) Conventional CT image showing the extent of the tumour. (B) Colour map for BF; there is a greater presence of yellow colour shades with red traces, representing higher BF values within the tumour than in the normal tissues. (C) Colour map for BV; there is a greater presence of red colour shades representing higher BV values within the tumour than in the normal tissues. (D) Colour map for MTT; there is a greater presence of blue colour shades representing lower MTT values within the tumour than in the normal tissues. (E) Colour map for PS; there is a greater presence of red colour shades representing higher PS values within the tumour than in the normal tissues.

Figure 4

A 53-year-old woman with liver metastases from breast cancer. Conventional CT images and colour maps before (A,B) and after (C,D) 4 weeks of treatment with metronomic oral vinorelbine. (A) Conventional CT image showing a hypodense metastatic lesion in the VII liver segment. (B) Colour map for BF showing a peripheral rim of yellow colour shades along the margins of the lesion, representing higher BF values than in the surrounding liver parenchyma. (C) Conventional CT performed after 4 weeks of treatment with metronomic oral vinorelbine, showing only a minimal reduction in size, not yet sufficient to be classified as response to therapy according to the RECIST criteria. (D) Colour map for BF after 4 weeks of treatment with metronomic oral vinorelbine, showing almost complete disappearance of the peripheral rim along the margins of the lesion, accounting for a decrease in BF values.