Development of a Noncontrast Gated Aortic Computer Tomography Protocol for Aortic Screening and Surveillance

Abstract

Computed tomography (CT) evaluation can effectively gauge the presence and size of aneurysms in both chest and abdomen. This is advantageous compared to ultrasound imaging; however, the existing CT protocols are limited by high radiation dose, risk of complication from workup of incidental findings, and high cost of radiologist interpretation time. We present a low-risk and low-cost CT protocol—the noncontrast gated aortic (NCGA) CT—that allows for evaluation of aortic aneurysm pathology. Patients requiring CT scan for surveillance of known aortic pathology were consented for an additional CT scan of the chest, abdomen, and pelvis. Patients underwent a topogram, which allows the CT machine to suggest optimal parameters for imaging the patient’s size and tissue density. Our protocol involved changing parameters that affect dose, including voltage (kV) and tube current-time product (mAs). Postprocessing was applied to optimize image quality and limit the surrounding visible field. Each study was independently reviewed by three qualified physicians to assess adequacy of the study and maximum size of the aorta in each of four segments (ascending, transverse arch, descending thoracic, and abdominal). Assessment of each study was used to modify the protocol for the next patient. Nine patients (8 males, 1 female) were studied. Comparison of NCGA CT protocol and regular protocol in radiation dose, image quality and reading time is shown in the Table. The optimal parameters of 80 kV and one-fifth of the recommended mAs were refined by the sixth patient. Collimation into four separate segments of the aorta minimized visible volume of nonaortic tissues. Interpretation time for the final three studies averaged 30 seconds. Our final protocol allowed adequate definition of the aorta and resulted in an effective dose of between 0.19 and 0.33 mSv, which is equivalent to two to three chest x-rays, 30- to 50-times less than the standard CT chest, abdomen, and pelvis scan. A NCGA CT scan can be performed on currently available CT devices with two to three chest x-rays worth of radiation, minimal risk of incidental findings, and low interpretation time. Such a study protocol may be a useful alternative to standard protocols for aortic aneurysm screening and surveillance.TableComparison of noncontrast gated aortic (NCGA) computed tomography (CT) protocol to regular CT in radiation dose, image quality, and reading timePatient% of Normal CT mAs (%)Dose (mSievert)Image qualityReading rime (sec)198.391.53Excessive27214.490.22Borderline32325.200.41Adequate34411.270.08Inadequate34521.900.13Inadequate30616.500.25Inadequate32721.210.33Adequate27820.310.22Adequate29920.000.19Adequate33 Open table in a new tab