Reduced time CT perfusion acquisitions are sufficient to measure the permeability surface area product with a deconvolution method

Purpose: The acquisition time in CT perfusion studies significantly affects patient’s dose exposure. In order to reduce the radiation dose, reduced time CT perfusion acquisitions are tested to measure PS with a deconvolution method. Methods and Materials: PS was calculated with repeated measurements (n=259) while truncating the time density curve at different time values in 11 CT perfusion studies conducted for lung cancer (n=2), Hodgkin lymphoma (n=7) and renal cell carcinoma (n=2), using CT perfusion 4D software (GE Healthcare). The median acquisition time of CT perfusion studies was 62 sec (range 49-120 sec). To verify the accuracy of the deconvolution algorithm, a variation of the truncated PS within the error measurements was searched, i.e. within 3 standard deviations from the mean nominal error provided by the software. As a sanity check the test was performed for all the parameters measured using CT Perfusion 4D software. Results: PS was consistent within 7% in ~10 to ~20 seconds; and within 0.9% in ~20 to ~23 seconds; PS was constant after 25 to 35 sec. A consistent result lasted for all the observed parameters (MTT, BV, BF) as expected from their analytical dependence. Conclusion: Thirty-five seconds are enough to obtain a reliable IRF (impulse residual function). For an accurate measurement of the PS a 45 sec acquisition time should be an optimal compromise to obtain reliable PS measurements and a reasonable dose exposure. No additional information can be provided with longer perfusion acquisition times.