CTA of the abdominal aorta at 80 kV and 100 kV and reduced contrast medium

Since the introduction of MDCT technology, CT angiography (CTA) has become a
standard tool for the evaluation of disease of the aorta and its major
branches. As the use of MDCT has become routine in clinical practice, concerns
have been raised regarding radiation exposure. The current literature assumes
a small but not negligible risk for radiation induced cancer from CT
examinations. With still an increasing number of CT examinations yearly,
reduction of the radiation dose from CT is an important issue.

Lowering the tube voltage represents an important radiation reduction approach
because the radiation dose varies with the square of the tube voltage. Hence,
lowering the tube kilo voltage (kV) can substantially increase the contrast
enhancement of vascular structures while simultaneously reducing radiation dose
to the patient. The downside of low tube potential CT is the nonlinear increase
in image noise, therefore it is necessary to adjust the CT tube current in
order to maintain a constant image quality.

In our latest study *Abdominal aorta CTA at 80 kV and a reduced amount of
contrast medium: A comparative analysis of image quality and radiation dose*
the quantitative and qualitative results showed that more patients could be
scanned with the use of 80 kV and the use of 30 mL of contrast medium instead
of the clinical standard (120 kV and the use of 50 mL of contrast medium). The
80 kV images showed more image noise, however this did not resulted in
diminished subjective image quality, as the increased attenuation of the
iodinated contrast medium and the high attenuation difference between the
arterial system and the poorly enhanced surrounding tissues can partially
offset the greater image noise.

In a previously performed study we used a test bolus injection protocol with a
test bolus of 10 mL contrast medium to synchronize the data acquisition with
the arrival of contrast material in the abdominal aorta. The test bolus was
followed by a diagnostic bolus injection of 20 mL 1:1 with saline diluted
contrast medium. This resulted in a total contrast medium volume injection of
30 mL ioversol 350. It is widely accepted that heavy patients need more
contrast medium than slim individuals to reach the same vessel enhancement. To
personalize the amount of contrast medium of the diagnostic bolus, the
diagnostic bolus in both BMI groups will be based on the *Lean body mass* (LBM)
of the patients. The LBM is used as the basis to calculate contrast material
dose for CTA, because LBM reflects the blood vessel volume better than a dose
based on the patients weight in kilograms.

The goal of this study is to reduce the effective radiation dose and improve
the image quality by a personalized amount of contrast medium in CTA of the
abdominal aorta.

Intervention study, feasibility study

In total 90 patients who are referred for a CTA of the abdominal aorta
according to clinical indications will be included. The patients will be
divided into the low- (BMI < 28 kg/m2) and high- (BMI >= 28 kg/m2) body mass
index (BMI) group. The patients will be scanned with the following CT scan
parameters:
• Low BMI group scan with 80 kV
• High BMI group scan with 100 kV

In a previously performed study we used a test bolus injection protocol with a
test bolus of 10 mL contrast medium to synchronize the data acquisition with
the arrival of contrast material in the abdominal aorta. The test bolus was
followed by a diagnostic bolus injection of 20 mL 1:1 with saline diluted
contrast medium. This resulted in a total contrast medium volume injection of
30 mL ioversol 350.

To personalize the amount of contrast medium of the diagnostic bolus, the
diagnostic bolus in both BMI groups will be based on the *Lean body mass* (LBM)
of the patients. The LBM is used as the basis to calculate contrast material
dose for CTA, because LBM reflects the blood vessel volume better than a dose
based on the patients weight in kilograms.

Based on the results of our previous performed study, the diagnostic bolus in
patients in the low BMI group will be dosed with 0.4 mL of iodinated contrast
medium per LBM. Patients in the high BMI group will be dosed with 0.6 mL of
iodinated contrast medium per LBM. The diagnostic bolus injection will be
diluted 1:1 with a saline chasing bolus.

There is a risk that the scans of the patients in the low BMI protocol will be
of less quality, since less kV is used. Worst case scenario is that the patient
will have to undergo a second scan. Immediately after scanning the patients,
the scans will be looked after a radiologist to see if the image quality is
sufficient. So when the image quality is not sufficient, patients will be
scanned immediately and an additional needle prick is not necessary.