Multidetector CT reduces radiation doses for combined CTP and CTA imaging
With a single rotation, the effective dose for combined CT perfusion (CTP) and CT angiography (CTA) imaging can be reduced to nearly one-third of the dose, or approximately 7-11 mSv, measured with the prototype 256-slice CT scanner, according to a poster presentation at the American Heart Association conference held this week in Orlando, Fla.

Richard George and colleagues at Johns Hopkins University in Baltimore conducted the study.

The study sought to directly measure the radiation dose on subjects undergoing combined CTP and CTA imaging on a 256-slice CT scanner.

In the study, 15 patients underwent combined CTP and CTA imaging on a prototype 256-slice CT scanner from Toshiba Medical Systems. The scanner has 256 rows of 0.5 mm size detectors with the capability to scan 12.8 cm length in the axial plane per CT gantry rotation in 0.5 sec.

Direct-dose measurements were performed using a custom vest worn by the patient fitted with 15-25 thermoluminiscent dosimeters (TLDs). An anthropomorphic phantom was also scanned with the same protocol with TLDs positioned on the surface and inside the phantom at various organ locations. Effective doses were estimated based on the maximum surface dose.

The effective dose from TLD measurements ranged from 22 to 32 mSv for the entire protocol, based on the direct dose measured on subjects and not based on dose derived from phantom measurements as routinely done.

The researchers reported that the doses in this study are comparable to similarly measured doses from 64-slice coronary CTA alone. The prototype scanner uses 3 gantry rotations and a 1.5 second exposure time in its current configuration.

They concluded that since the 256-slice CT scanner can cover the entire heart in a single rotation, it eliminates the need for tissue overlap from low pitch values. The researchers also reported that efforts are currently underway to develop a prospective ECG-gated protocol that can limit radiation exposure to a single rotation for both stress and rest CTA scans.