Introduction: The purpose of this study was to directly measure the radiation dose on subjects undergoing combined CT Perfusion (CTP) and CT Angiography (CTA) imaging on a 256-row MDCT scanner. Methods: Fifteen patients underwent combined CTP and CTA imaging on a prototype 256 row MDCT scanner (Toshiba, Nasu, Japan). The prototype 256-row MDCT scanner consists of 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 secs. The protocol included a scout scan and test bolus scan followed by adenosine stress CTP (120 kVp, 200 mA, gantry rotation speed of 0.5 secs for 3 rotations, 128x1.0 mm) and rest CTA (120 kVp, 350 mA, gantry rotation speed of 0.5 secs for 3 rotations, 256x0.5 mm) in an axial scan mode. Direct dose measurements were performed using a custom vest worn by the patient fitted with 15–25 thermoluminiscent dosimeters (TLDs) (Landauer, IL) placed in AP and lateral locations. 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 according to previously validated methodology. Results: The effective dose from TLD measurements ranged from 22 to 32 mSv for the entire protocol. This is based on direct dose measured on subjects and not based on dose derived from phantom measurements as done routinely. Conclusions: The doses reported in this study are comparable to similarly measured doses from 64-slice MDCT coronary angiography alone. This prototype scanner uses 3 gantry rotations and a 1.5 second exposure time in it current configuration. Since, 256-row MDCT can cover the entire heart in a single rotation, it eliminates the need for tissue overlap from low pitch values. 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. With a single rotation, the effective dose can be reduced to nearly one-third of the dose measured with this prototype, or approximately 7–11 mSv for a combined CTP and CTA imaging.
AimPrevious animal studies have demonstrated differences in perfusion and perfusion reserve between the subendocardium and subepicardium. 320-row computed tomography (CT) with sub-millimetre spatial resolution allows for the assessment of transmural differences in myocardial perfusion reserve (MPR) in humans. We aimed to test the hypothesis that MPR in all myocardial layers is determined by age, gender, and cardiovascular risk profile in patients with ischaemic symptoms or equivalent but without obstructive coronary artery disease (CAD).
BACKGROUND: The blood brain barrier (BBB) makes it difficult for oral or intravenous chemotherapy to achieve therapeutic concentrations in brain parenchyma. Regadenoson is an adenosine receptor agonist which transiently disrupts the BBB, allowing systemically administered high molecular weight dextran (MW 70kD) to enter normal rodent brain. Our recent studies with this compound suggest that temozolomide concentrations in rodent brain are also increased by regadenoson. This FDA approved agent is used routinely for cardiac stress tests in patients unable to exercise along with visipaque and cardiac computed tomography (CT) imaging. Visipaque (MW 1550) typically only enters brain where there is significant disruption of the BBB. This study is being conducted to determine if regadenoson will allow more contrast to enter normal human brain. METHODS: Patients without known intracranial disease who were undergoing clinically indicated pharmacologic cardiac stress tests (visipaque with cardiac CT followed by visipaque with regadenoson and cardiac CT) were eligible. This IRB approved study only added brain CT pre- and post-regadenoson. Contrast delivery was measured in hounsfield units (HU), at the level of the basal ganglia, within the cortex, deep gray and white matter. A total of 27 patients are required to assist in comparison analysis of regional contrast uptake. A matched-pairs t-test was performed to determine if the difference was significant. RESULTS: Five of the 27 patients have been accrued and analyzed. There was no difference in contrast following visipaque alone and visipaque with regadenoson (29.3HU vs 30.2HU respectively, P = 0.06). CONCLUSION: Early results from this ongoing study suggest that even accounting for the additional visipaque dose there is a trend towards increased contrast enhancement following regadenoson administration in patients with presumably normal brains. Transient disruption of the BBB to facilitate drug entry using an FDA approved agent could be of significant importance to the field of neuro-oncology.
