Not "TSTC" anymore

50 year old male presents for staging of rectal cancer. Conventional CT shows a solitary liver lesion measuring 6-7 mm in size.

Too small to characterize? Recommend MRI? Not anymore, thanks to spectral CT! 

This recent paper from Duke and Stanford talks about using single phase contrast enhanced CT to characterize indeterminate liver lesions with iodine quantification. The cut-off they use to differentiate a benign from malignant lesion was 1.2 ± 0.1 mg/mL of iodine in the lesion.

Our lesion has no iodine uptake on visual analysis, and on quantification, iodine content is 0.0 mg/mL. Spectral curve is downsloping on the left, consistent with no iodine content. Voila, this is a benign lesion, likely a simple cyst, and needs no further workup. 

There is, of course, more to this. We have a great need to standardize techniques and generate data regarding normal, and abnormal, values. There will be differences between vendors, but as far as possible, we need to make this vendor neutral.

Conventional CT: Notice tiny liver lesion.

Conventional CT: At 28.5 HU, this lesion is "too small to characterize".

Iodine map: No uptake on visual analysis.

Measured iodine uptake in the lesion (blue ROI) is zero! For comparison measured iodine uptake in background liver (red ROI) is about 1.1 mg/mL.

Spectral curves: Blue curve in lesion is downsloping on lower energy, consistent with no iodine uptake. Normal background liver (magenta curve) shows increased density on lower energy.