Effect of dose reduction on cerebral CT perfusion maps: results from a hybrid digital perfusion phantom

Purpose: To quantitatively evaluate the effect of dose reduction of a standard head CTP protocol on the perfusion maps. Material and Methods: A hybrid digital perfusion phantom was used to simulate dose reduction in a CT perfusion acquisition. Noise patterns were obtained by scanning an epoxy filled human skull phantom on multiple mAs levels on a 320-row scanner and combined with tissue attenuation curves obtained from 5 patient data for grey matter (GM), white matter (WM), artery and vein. We simulated a real clinical CTP head protocol available on the Toshiba CT console (1 scan at 200 mAs, 13 scans at 100 mAs, 5 scans at 75 mAs and all at 80 kV) with a total duration of 55s (5mm slab thickness) and artificially reduced the dose from 100% to 10% in steps of 10%. CBF, CBV and MTT maps were calculated using PMA (ASIST-JAPAN). Mean values of GM and WM were evaluated. Results: Absolute CBF and CBV values stay within 20% of the values at original dose for CTP acquisitions at more than 50% of the original dose for both GM and WM. At 10% of the original dose, WM CBV values were overestimated with 24-107%, GM CBV values with 4-32%, and WM CBF values with 42-106%. GM CBF values were within 20% of the values at 100% of original dose. MTT values were less affected by dose reduction. Conclusion: Absolute CBF and CBV values require sufficient dose to be correct: values at low dose are overestimated.