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Absolute Blood Flow Measurement in a Cardiac Phantom Using Low Dose CT

B Ziemer

B Ziemer*, L Hubbard , J Lipinski , S Molloi , University of California, Irvine, CA


TU-A-12A-9 Tuesday 7:30AM - 9:30AM Room: 12A

Purpose: To investigate a first pass analysis technique to measure absolute flow from low dose CT images in a cardiac phantom. This technique can be combined with a myocardial mass assignment to yield absolute perfusion using only two volume scans and reduce the radiation dose to the patient.

Methods: A four-chamber cardiac phantom and perfusion chamber were constructed from poly-acrylic and connected with tubing to approximate anatomical features. The system was connected to a pulsatile pump, input/output reservoirs and power contrast injector. Flow was varied in the range of 1-2.67 mL/s with the pump operating at 60 beats/min. The system was imaged once a second for 14 seconds with a 320-row scanner (Toshiba Medical Systems) using a contrast-enhanced, prospective-gated cardiac perfusion protocol. Flow was calculated by the following steps: subsequent images of the perfusion volume were subtracted to find the contrast entering the volume; this was normalized by an upstream, known volume region to convert Hounsfield (HU) values to concentration; this was divided by the subtracted images time difference. The technique requires a relatively stable input contrast concentration and no contrast can leave the perfusion volume before the flow measurement is completed.

Results: The flow calculated from the images showed an excellent correlation with the known rates. The data was fit to a linear function with slope 1.03, intercept 0.02 and an R² value of 0.99. The average root mean square (RMS) error was 0.15 mL/s and the average standard deviation was 0.14 mL/s. The flow rate was stable within 7.7% across the full scan and served to validate model assumptions.

Conclusion: Accurate, absolute flow rates were measured from CT images using a conservation of mass model. Measurements can be made using two volume scans which can substantially reduce the radiation dose compared with current dynamic perfusion techniques.

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