Abdominal computed tomographic (CT) is an important prognostic tool with regard to the detection of oncological, infectious and other abdominal disorders.

The total iodine load (TIL) is regarded as a decisive factor in the opacification of parenchymal structures. The EICAR trial demonstrated that injection with high flow rates of prewarmed contrast media (CM) was safe and patients did not experience any pain, stress of discomfort during injection. Flow rates as high as 8.8 ml/s were injected without any discomfort. All concentrations used (e.g. 240, 300 and 370 mg I/ml) in this study were prewarmed. According to the recent recommendations (ESUR guidelines 10.0) it should be considered to warm iodine-based CM before administration. The hypothesis is that although using CM at room temperature (~23°C [~73°F]) might result in lower attenuation of the liver parenchyma than would be achieved using CM pre-warmed to body temperature, diagnostic image quality, patient safety and comfort will not be compromised by not pre-warming CM in this setting. According to the guidelines, it is regarded as best clinical practice to pre-warm CM. Surprisingly, these recommendations are merely based on a hypothetical assumption. In the literature, there are no studies evaluating this topic and it has never been clearly shown to result in a better patient comfort. For this reason, many clinics do not pre-warm their CM in daily clinical routine. Only one study evaluated subjective comfort in hysterosalpingography (HSG), in which CM is injected in to the cavity of the uterus. This study found that prewarmed CM alleviates the pain and decreased the incidence of vasovagal episodes during HSG. To the best of our knowledge, no study showed that prewarmed CM in CT resulted in higher patient comfort, in comparison to CM at room temperature (20° C).

Up till now, all CM in the department is prewarmed. In case this study does not show a difference in patient comfort, prewarming the CM can be stopped, resulting in a considerable simplified workflow.

The hypothesis is that usage of CM at room temperature (20° C) might result in a decreased level of patient comfort in abdominal CT, in comparison to pre-heated (37° C) CM, with no significant difference in diagnostic attenuation of the liver parenchyma between groups.

Abdominal computed tomography (CT) scans are performed daily on a regular basis. Since its advent, rapid technical advances in CT continuously improved image quality. Besides scan technique, the contrast media (CM) injection protocol is the crucial factor in abdominal imaging. Parenchymal contrast enhancement is determined by patient related factors (e.g. cardiac output, blood volume and patient weight), the CM injection protocol and the scan protocol. Much literature has been performed with regard to optimizing CM application and the scan protocol. Flow rate of the CM and patient discomfort have been thoroughly investigated in our department. Heating CM up to body temperature has been daily clinical routine in our department for years.

According to the recent recommendations (ESUR guidelines 10.0) it is advised to warm iodine-based CM before administration. Warming the CM is expected to result in a higher patient comfort, based on clinical observation. Kok et al. showed in phantom experiments that high temperature, low iodine concentration and low viscosity significantly decreases injection pressure. Subsequently, as increased temperature reduces the viscosity of the CM, the decreased viscosity is hypothesized to reduce the risk of extravasation. A decreased viscosity might also have a substantial impact on individual tailored CM injection protocols in daily routine scanning as it is speculated that a decrease of viscosity and subsequent decrease in peak injection pressure could influence patient comfort during injection. The EICAR trial showed that prewarmed CM can be safely injected at high flow rates, without patient discomfort, pain or stress. However, the latter was not compared to CM at room temperature.

Different CM concentrations are used in different hospitals throughout the world. The higher the concentration, the higher the viscosity of the CM. In present study, only one CM concentrations (e.g. 300 mg/ml) will be used, which is used in daily clinical practice for years. Heating the CM decreases the viscosity. It is therefore expected that the preheated CM in a concentration of 300 mg/ml has a lower viscosity in comparison to the CM at 20° C.

Pre-warming CM might be regarded as best clinical practice. No studies have been performed to investigate this statement, nor is there any literature that shows that prewarmed CM has a favorable patient comfort compared to CM injected at room temperature. For these reasons, there remains to be some reluctance and many clinics still not pre-warm their CM. One study, in which CM is injected in to the cavity of the uterus to check for any anatomical variants and causes for infertility, showed a preference for prewarmed CM in hysterosalpingography (HCG). This study found that prewarmed CM alleviates the pain and decreased the incidence of vasovagal episode during the HCG.

The hypothesis is that although using CM at room temperature (~23°C [~73°F]) might result in lower attenuation of the liver parenchyma than would be achieved using CM pre-warmed to body temperature, diagnostic image quality, patient safety and comfort will not be compromised by not pre-warming CM in this setting. Pre-warming CM requires special equipment and more complex planning and logistics. On the other hand, pre-warming CM may yield higher attenuation levels, comfort and image quality. In case this study does not show a significant difference in patient comfort and diagnostic quality between groups, pre-warming the CM can be stopped, resulting in a considerable simplified workflow.

Inclusion criteria

• Patients referred for abdominal CT
• Patient ≥ 18 years old and competent to sign informed consent

Exclusion criteria

• Hemodynamic instability
• Pregnancy
• Renal insufficiency defined as glomerular filtration rate (GFR) < 30ml/min/1.73m2 (Odin protocol 004720)
• Iodine allergy (Odin protocol 022199)
• Age < 18 year
• Unable to give informed consent or no informed consent obtained
• Inability to position an 18 gauge cannula in an antecubital vein

The results will be published in international peer reviewed journals in order to spread new insights regarding contrast media temperature in abdominal CT imaging. Both positive and negative results will be published according to the guidelines of the 'Centrale Commissie Mensgebonden Onderzoek' (CCMO).

Within 18 months after completion

All subjects will be randomized into two different groups as listed in the study outline.

The randomization schedule will be prepared and centrally administered. A computer random number generator prepares the randomization schedule in a 1:1 fashion (balanced randomization). Stratification is performed, based on age (< 60 and ≥ 60 years) and weight (< 80 and ≥ 80 kg). Variable block randomization will distribute patients equally over time.

The blinding and randomization process will be conducted by Clinical Trial Centre Maastricht (CTCM, www.CTCM.nl) with a randomization program designed for usage of different techniques (minimization, block method, biased-coin, etc). The technician who administers the CM is aware of the CM temperature. Therefore, the technicians will be instructed before start of the study, not to give this information to the patient, not even when requested by the patient.