The relationship between contrast media volume and tube voltage in computed tomography of the liver, for optimal enhancement based on total body weight: A randomized controlled trial. [COMpLEx trial]

Computed Tomography (CT) is a non-invasive imaging tool, used for a great
variety of indications. Contrast media (CM) is used to enhance vascular
structures and organ parenchyma. The visibility of liver lesions depends mainly
on the ratio between the size and the difference of the lesion to the
background. A large lesion might be visible without administration of CM,
whilst a smaller lesion needs the addition of CM to become visible.
Additionally, CM can be useful in the characterisation of liver lesions. Heiken
et al. (1995) found that an attenuation of the parenchyma after CM
administration of at least * 50 Hounsfield units (HU) compared to an unenhanced
scan (in the same patient) is necessary to recognize liver lesions. They
proposed a dosing factor of 0.521 g I/kg to be necessary to reach such
attenuation at a tube voltage of 120 kV [1].
The parenchymal enhancement depends on patient, CT scanner and CM factors.
Weight, height, cardiac output, age, gender, venous access, breath-holding,
renal function and comorbidity all fall under patient factors [8]. Recently
much research showed preferable outcomes for individualized CM injection
protocols, in which the contrast bolus is adapted to patient TBW, LBW or body
surface area (BSA) [6, 7, 9, 11-13]. In a recent feasibility study in our
department, we evaluated the attenuation of the liver parenchyma. Results
showed that a body weight adapted CM injection protocol resulted in more
homogeneous liver enhancement compared to a fixed CM dose (not published yet).
With recent technological developments in X-ray tube technology it became
possible to use lower tube voltages. As a result making it possible to perform
scans with a sufficient image quality (IQ) and a low tube voltage and therefore
a lower radiation dose [10]. Another advantage lies in the fact that reducing
the tube voltage, approaching 33 keV k-edge of iodine, results in an increase
in attenuation of the iodine. The new technological developments make it
possible to reduce the radiation dose and CM volume at the same time.
As recommended by the supplier, it is possible to calculate the total iodine
load (TIL) that can be spared with the use of lower kV settings [14]. A
reduction of 10 kV should result in a 10% reduction in CM volume. Reducing the
tube voltage from 120 to 90 kV should therefore lead to a 30% reduction in CM
volume. As mentioned before it is preferred to use an individualized CM
injection protocol based on TBW or LBW. For this study, we have adapted this
theory to the concept of TBW. Table 1. below indicates which dosing factors
should be used for each kV setting, based on the recommendations mentioned in
the above.

The aim of present study is to investigate if adapting the dosing factor based
on TBW and therefore the CM volume to the tube voltage used, results in a more
homogeneous liver enhancement. We hope to find a more homogeneous enhancement
between patients and in the same patient, regardless of body composition and
tube voltage used.

This study is a randomized controlled trial conducted according to Guidelines
of GCP. This prospective study will assess the liver enhancement with regard to
TBW adapted individualized injection protocols and kV setting.
We are aiming to prospectively enrol 64 patients in each arm. The inclusion
period will be two years. All patients referred for an abdominal or liver CT
scan, with or without a chest CT, will be eligible for inclusion. Technicians
will schedule patients on the 3rd generation DSCT (SOMATOM Force, Siemens
Healthineers) depending on clinical program and logistics. The patient will be
scheduled in one of four arms (figure 1):
1. CM injection protocol with a dosing factor of 0.521 grams of Iodine per kg
of TBW and a tube voltage of 120 kV.
2. CM injection protocol with a dosing factor of 0.521 grams of Iodine per kg
of TBW and a tube voltage of 90 kV.
3. CM injection protocol with a dosing factor of 0.417 grams of Iodine per kg
of TBW and a tube voltage of 100 kV.
4. CM injection protocol with a dosing factor of 0.365 grams of Iodine per kg
of TBW and a tube voltage of 90 kV.
All patients scheduled for a CT scan, which includes a portal venous phase
abdominal scan, will be included. In case an unenhanced CT is not part of the
scan protocol, one unenhanced slice at the level of the portal vein will be
added to the protocol before administration of CM.

NVT

The participants will receive a scan based on referral from their clinician and
the scan will be performed according to normal clinical routine. Only patients
already scheduled for clinically mandated abdominal CT will be recruited. A
very small extra amount of radiation dose will be given to the patient, in
order to acquire a single, unenhanced CT slice of the liver. Differences in
attenuation, because various tube voltages and CM volumes are used, may
potentially impact the diagnostic accuracy of the abdominal CT, especially when
the attenuation is below a diagnostic level. However, since the CM volume is
adapted to the lower tube voltages and these lower kV settings and CM volumes
are already described in different papers with sufficient diagnostic IQ, it is
expected that the attenuation will be sufficient. Also, CareDose 4DTM is used
to guarantee an IQ as specified by the supplier.
Participation in this study will not cause any delay in the standard CT
procedure. We therefore do not expect participation in this study to give any
disadvantages for the subjects relative to the standard CT protocol, which they
would have undergone as part of their clinical care.