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British Journal of Radiology (2004) 77, 821-830
© 2004 British Institute of Radiology
doi: 10.1259/bjr/19527646
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Full Paper

Effect of iodine concentration of contrast media on contrast enhancement in multislice CT of the pancreas

S Fenchel, MD 1,2 T R Fleiter, MD 1,2 A J Aschoff, MD 1 R van Gessel, PhD 3 H-J Brambs, MD 1 and E M Merkle, MD 1,2

1 Department of Radiology, University of Ulm, Steinhoevelstr. 9, 89075 Ulm, Germany, 2 Department of Radiology, University Hospitals of Cleveland/Case Western Reserve University, 11100 Euclid Avenue, Cleveland, OH 44106, USA and 3 Bracco Altana Pharma GmbH, Max-Stromeyer- Str. 57, 78467 Konstanz, Germany

Correspondence: Sabine Fenchel, Department of Radiology, University of Ulm, Steinhövelstr. 9, D-89075 Ulm, Germany


   Abstract
Top
 Abstract
Introduction
 Materials and methods
 Results
 Discussion
 References
 
The purpose of this study was to determine the influence of two different iodine concentrations of the non-ionic contrast agent, Iomeprol, on contrast enhancement in multislice CT (MSCT) of the pancreas. To achieve this MSCT of the pancreas was performed in 50 patients (mean age 57±14 years) with suspected or known pancreatic tumours. The patients were randomly assigned to group A (n=25 patients) or group B (n=25 patients). There were no statistically significant differences in age, height or weight between the patients of the two groups. The contrast agent, Iomeprol, was injected with iodine concentrations of 300 mg ml–1 in group A (130 ml, injection rate 5 ml s–1) and 400 mg ml–1 in group B (98 ml, injection rate 5 ml s–1). Arterial and portal venous phase contrast enhancement (HU) of the vessels, organs, and pancreatic masses were measured and a qualitative image assessment was performed by two independent readers. In the arterial phase, Iomeprol 400 led to a significantly greater enhancement in the aorta, superior mesenteric artery, coeliac trunk, pancreas, pancreatic carcinomas, kidneys, spleen and wall of the small intestine than Iomeprol 300. Portal venous phase enhancement was significantly greater in the pancreas, pancreatic carcinomas, wall of the small intestine and portal vein with Iomeprol 400. The two independent readers considered Iomeprol 400 superior over Iomeprol 300 concerning technical quality, contribution of the contrast agent to the diagnostic value, and evaluability of vessels in the arterial phase. No differences were found for tumour delineation and evaluability of infiltration of organs adjacent to the pancreas between the two iodine concentrations. In conclusion the higher iodine concentration leads to a higher arterial phase contrast enhancement of large and small arteries in MSCT of the pancreas and therefore improves the evaluability of vessels in the arterial phase.


   Introduction
Top
 Abstract
 Introduction
Materials and methods
 Results
 Discussion
 References
 
The introduction of multislice CT (MSCT) has revolutionized the field of computed tomography and has created new dimensions in temporal and spatial resolution in CT scanning. In MSCT of the pancreas separate acquisition of defined perfusion phases has become standard with acquisition times of 10–15 s for each contrast phase and slice collimations of between 1 mm and 3 mm [1–13]. The most common clinical indications for MSCT of the pancreas are diagnosis of acute and chronic pancreatitis, detection and characterization of pancreatic tumours, and determination of tumour resectability when a lesion appears to be malignant [8, 14]. Since visualization of anatomical structures and pathology is improved by contrast administration, it is necessary to adapt contrast material protocols to the higher scanning speed of multislice CT scanners. Currently non-ionic contrast agents with an iodine concentration of 300 mg ml–1 or 370 mg ml–1 are most commonly used and are applied at flow rates of 3–5 ml s–1 [1, 4, 7, 11, 15, 16]. The recommended maximum amount of applied iodine is 35–45 g [8, 17, 18]; this will probably not change significantly. Higher early contrast medium uptake can be achieved either by increased contrast medium concentrations or by increased flow rates [1, 4, 7, 8, 19]. Since increasing the flow rate is limited by the vessel diameter, concentration of the contrast medium solution is a parameter that can still be optimized.

In this study we investigated the influence of two different iodine concentrations of the non-ionic, monomeric contrast material, Iomeprol, on contrast enhancement in MSCT of the pancreas in patients with known or suspected pancreatic tumours and patients after pancreatic surgery; we also evaluated the influence of the iodine concentration on the diagnostic value.


   Materials and methods
Top
 Abstract
 Introduction
 Materials and methods
Results
 Discussion
 References
 
Patients
From December 2000 to September 2001, 50 consecutive patients, who were referred to our department for CT of the pancreas because of known or suspected pancreatic tumours or for post-operative follow-up after pancreatic surgery, were enrolled in this prospective randomized parallel-group study after having given their written informed consent. The size of the cohort was pre-determined to 50 patients. Excluded from the study were patients with hyperthyroidism (thyroid stimulating hormone (TSH) decrease), hypersensitivity to iodinated contrast agents, renal failure (serum creatinine level >108 µmol l–1), alcohol or drug abuse, insulin-dependent diabetes mellitus, pregnant patients or nursing women, patients less than 18 years of age and patients who had participated in another study within the past 30 days. The patient population included 20 women and 30 men, who were 22–76 years old (mean age 57±14 years) and who weighed 43–91 kg (mean 68±12 kg). The patients were randomly assigned to group A or group B, each of which differed in contrast material concentration and intravenous injection volume. Each group consisted of 25 patients. The study was approved by both the Institutional Review Board and the Ethics Committee of the regional Physicians' Chamber.

CT protocol
The CT examination was performed after oral administration of water (500 ml) and with the patient positioned left side up in the scanner to achieve water distension of the duodenum. The non-ionic monomeric contrast material Iomeprol (Bracco Altana Pharma GmbH, Konstanz, Germany) was applied with an iodine concentration of 300 mg ml–1 (Iomeprol 300) and a volume of 130 ml in group A and with an iodine concentration of 400 mg ml–1 (Iomeprol 400) and a volume of 98 ml in group B (Table 1Go). The amount of injected iodine was approximately 39 g in both groups. Iomeprol was heated to a temperature of 37°C and injected with a flow rate of 5 ml s–1 with an automatic injector through a 20 gauge plastic cannula placed in a cubital vein in both groups.


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  		Table 1. Technical parameters of pancreatic multislice CT imaging

 
MSCT (MX8000; Philips, Cleveland, OH) of the pancreas was performed in all patients prior to contrast medium administration as well as in the arterial and portal venous phases following contrast administration. The beginning of the arterial phase scan was determined individually by the test bolus technique: single-level serial CT images were obtained at the level of the pancreatic head and the superior mesenteric artery (SMA) during a single breath hold every second from 0 s to 40 s after injection of a contrast bolus of 30 ml (flow rate 5 ml s–1) with an automatic injector (Iomeprol 300 in group A, Iomeprol 400 in group B). The time to peak enhancement in the aorta was taken as the scan delay for the arterial phase scan. The portal venous phase scan was started immediately after the arterial phase scan was completed (about 50–70 s after initiation of contrast medium injection). The acquisition parameters of the unenhanced, arterial and portal venous phase scans are listed in Table 1Go.

Data analysis
The presence of pancreatic masses and other pancreatic or abdominal pathologies on the CT scans was determined by two experienced radiologists in consensus according to morphological criteria and contrast enhancement patterns. Pathological CT findings were confirmed by the patient's history, laparoscopy, or follow-up CT scans.

Pathological pancreatic masses were detected in 15 patients of our study group by CT. 11 of the 15 pancreatic masses were proved pancreatic carcinomas (group A: n=6, group B: n=5) and four were pancreatic cysts (group A: n=3, group B: n=1). For the following quantitative and qualitative evaluation of the pancreatic masses, we included the 11 pancreatic carcinomas only and excluded the 4 pancreatic cysts since our absolute number of pancreatic masses was small (n=15) and the number of cysts was distinctively different between the two groups.

For quantitative assessment of contrast enhancement, circular regions of interest (ROIs) with diameters between 5 mm and 2 cm, depending on the size of the anatomical structure, were placed on the aorta, coeliac trunk, SMA, portal vein, liver, spleen, pancreas and pancreatic carcinomas. Contrast enhancement of the kidneys and the wall of the small intestine was evaluated by irregular ROIs placed on the renal cortex and on the wall of the small intestine. Attenuation (HU) was measured in the above-named organs, blood vessels and pancreatic carcinomas at three different locations before contrast administration, in the arterial and portal venous phases, and mean attenuation of each organ, blood vessel and pancreatic carcinoma was calculated in each phase. In the liver, pancreas, spleen and kidneys, visible blood vessels, bile ducts, the pancreatic duct and possible hepatic or pancreatic lesions were excluded from the ROI measurements. Contrast enhancement of the organs, blood vessels and pancreatic carcinomas in the arterial and portal venous phases was calculated as the difference between the contrast-enhanced and unenhanced scans. In patients with proved pancreatic carcinoma, differences between the mean attenuation values of the aorta, coeliac trunk, SMA and the pancreatic carcinoma and the difference between the mean attenuation values of the portal vein and the pancreatic carcinoma during the arterial and portal venous phase were calculated. Additionally, the difference between the mean normal pancreatic parenchymal attenuation value and the attenuation value of the pancreatic carcinoma – that is the tumour-to-pancreatic parenchymal attenuation difference – was calculated for the arterial and portal venous phase.

Qualitative image assessment was carried out independently by two experienced radiologists who were blinded to the study groups and other patient data. The following criteria were evaluated: the technical quality of the scans was assessed in four scores (excellent/good/sufficient/insufficient). In case of insufficient technical quality, further assessment was stopped and the reasons were stated. The contribution of the contrast agent to the diagnostic value was defined as the primary criterion and was assessed on a 10-point visual analogue scale as excellent (=10) to insufficient (=1). Secondary criteria contributing to the overall diagnostic value were assessed separately as five scores (excellent/good/sufficient/insufficient/other). Secondary criteria included tumour delineation from surrounding tissue, evaluability of infiltration of organs adjacent to the pancreas, evaluability of vessels in the arterial phase, and evaluability of vessels in the portal venous phase. Tumour delineation from surrounding tissue and evaluability of infiltration of organs adjacent to the pancreas were evaluated only for the patients with proved pancreatic malignancies, whereas evaluability of vessels in the arterial phase and evaluability of vessels in the portal venous phase were assessed for all patients.

Statistical analysis
For statistical analysis of contrast enhancement, mean enhancement values and standard deviations were calculated for the abovenamed organs, pancreatic carcinomas and vessels for each group. Mean attenuation differences and standard deviations between the aorta, coeliac trunk, SMA and the pancreatic carcinomas and between the portal vein and the pancreatic carcinomas and between the pancreas and the pancreatic carcinomas during the arterial and portal venous phases were calculated for each group. The differences between the two groups were evaluated by an exploratory t-test. A p-value <0.05 was considered statistically significant.

The primary criterion, contribution of the contrast agent to the diagnostic value, was analysed by summary statistics (mean, standard deviation, median, minimum, maximum), and the differences between the two groups were investigated by an exploratory t-test. A p-value <0.05 was considered statistically significant. The criteria of image quality, delineation of tumour from surrounding tissue, evaluability of infiltration of organs next to the pancreas, evaluability of vessels in the arterial phase, and evaluability of vessels in the portal venous phase, were presented by frequency distribution tables.


   Results
Top
 Abstract
 Introduction
 Materials and methods
 Results
Discussion
 References
 
Of the 50 patients we investigated, 4 presented with deviations from the study protocol and were subsequently excluded from the evaluation. Three belonged to group A (two technical failures during the scan, one extravasation) and one to group B (technical failure during the scan). There were no statistically significant differences in age, height or weight between the evaluated 46 patients of the two groups.

15 of the evaluated 46 patients presented with pancreatic masses on CT. All pancreatic masses were hypovascularized compared with the adjacent pancreatic parenchyma. 11 of the 15 pancreatic masses were proved pancreatic carcinomas (group A: n=6, group B: n=5) and 4 were pancreatic cysts (group A: n=3, group B: n=1). Two patients showed signs of acute pancreatitis without circumscribed pancreatic masses on CT (both group B) and 29 patients presented with a normal pancreas or an expected post-operative appearance after pancreatic surgery (group A: n=13, group B: n=16).

Delay of the arterial phase scan ranged from 11.00 s to 36.00 s with a mean of 17.02±4.41 s after start of the contrast injection. There were no statistically significant differences between the two groups (group A: mean 17.00±5.38 s, group B: mean 17.04±3.41 s).

The results of the quantitative contrast enhancement measurements are summarized in Table 2Go. In the arterial phase contrast enhancement was significantly higher in group B (400 mg iodine ml–1) than in group A (300 mg iodine ml–1) for the aorta, coeliac trunk, SMA, pancreas, pancreatic carcinomas, spleen, right and left kidney and the wall of the small intestine.


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  		Table 2. Mean contrast enhancement and standard deviations in blood vessels and organs during the arterial and portal venous phases in multislice CT of the pancreas after injection of Iomeprol 300 (300 mg iodine ml–1) and Iomeprol 400 (400 mg iodine ml–1)

 
In the portal venous phase, significantly higher contrast enhancement was found for the portal vein, the pancreas, the pancreatic carcinomas, and the wall of the small intestine in group B compared with group A (Table 2Go).

Attenuation differences in the arterial phase between the aorta and the pancreatic carcinomas, the coeliac trunk and the pancreatic carcinomas, and the SMA and the pancreatic carcinomas were significantly higher in group B compared with group A (Table 3Go).


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  		Table 3. Mean attenuation differences and standard deviations between blood vessels and pancreatic carcinomas as well as pancreatic parenchyma and pancreatic carcinomas during the arterial and portal venous phases in multislice CT of the pancreas after injection of Iomeprol 300 and Iomeprol 400

 
No statistically significant attenuation differences were measured between the pancreatic carcinomas and the pancreatic parenchyma in the arterial and portal venous phase between group A and group B (Table 3Go).

The differences in organ and blood vessel enhancement between Iomeprol 300 and 400 are demonstrated in Figures 1–3GoGoGo. In all figures window width was 350 HU and centre 50 HU.



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  		Figure 1. 63-year-old woman with carcinoma of the pancreatic head and dilation of the bile ducts and the pancreatic duct after injection of Iomeprol 400: (a) arterial phase scan, (b) portal venous phase scan. 66-year-old man with carcinoma of the pancreatic body, who received Iomeprol 300: (c) arterial phase scan, (d) portal venous phase scan. The higher arterial phase contrast enhancement with Iomeprol 400 (a) compared with Iomeprol 300 (c) for the large and small arteries, the pancreas and the kidneys as well as the higher portal venous phase enhancement for the pancreas and portal vein with Iomeprol 400 (b) compared with Iomeprol 300 (d) are demonstrated.

 



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  		Figure 2. 58-year-old woman after resection of the pancreatic tail because of a carcinoid tumour 3 years previously. The patient received Iomeprol 400: (a, b) arterial phase, (c, d) portal venous phase. 51-year-old man after Whipple procedure, who received Iomeprol 300: arterial phase (e, f), portal venous phase (g, h). Figures 2a–dGo show the higher arterial and portal venous phase contrast enhancement of the pancreatic head and body with Iomeprol 400 compared with the pancreatic body and tail of the patient in Figures 2e–hGo who had received Iomeprol 300. Additionally, the higher arterial phase contrast enhancement of the large and small arteries, the kidneys and the small intestine and the higher portal venous contrast enhancement of the portal vein and the small intestine with Iomeprol 400 (a–d) compared with Iomeprol 300 (e–h) are demonstrated.

 


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  		Figure 3. 34-year-old woman with chronic pancreatitis after injection of Iomeprol 400: (a) arterial phase, (b) portal venous phase. Figure 3aGo demonstrates the higher arterial phase contrast enhancement of the spleen with Iomeprol 400 compared with Iomeprol 300 (Figures 2e and fGo). Figure 3bGo shows the higher portal venous phase contrast enhancement for the portal vein with Iomeprol 400 compared with Iomeprol 300 (Figures 2g and hGo).

 
Concerning qualitative image assessment, the technical quality was judged as excellent, good or sufficient by both blinded readers in all 46 patients who were evaluated. There was a tendency on the part of both readers to consider the technical quality to be higher in the patients in group B (400 mg iodine ml–1).

The primary criterion, contribution of the contrast agent to the diagnostic value, was assessed on a scale from 1 to 10 (1=insufficient, 10=excellent). Reader 1 assigned to group A patients a range of scores between 8 and 10 with a mean of 9.2±0.9 and to group B patients scores between 7 and 10 with a mean of 9.8±0.7 (p=0.017, exploratory t-test). Reader 2 assigned a range of scores between 6 and 10 for both groups with a mean of 8.3±0.8 for group A and 8.7±1.1 for group B patients (not statistically significant). In general, Reader 2 assigned lower scores than Reader 1. The overall trend for both readers was to assign higher scores to group B patients (Iomeprol 400) than to group A patients (Iomeprol 300).

Secondary criteria
Delineation between tumour and surrounding tissue and evaluability of organ infiltration next to the pancreas was evaluated only for the 11 patients with proved pancreatic malignancies (11 pancreatic carcinomas). Delineation between tumour and surrounding tissue was assessed to be excellent for more group A patients (Iomeprol 300) than group B patients (Iomeprol 400). Concerning evaluability of organ infiltration next to the pancreas both readers tended to assign group A patients (Iomeprol 300) to higher categories than group B patients (Iomeprol 400).

Evaluability of vessels in the arterial and portal venous phase was judged in all 46 patients. Evaluability of vessels in the arterial phase was assessed to be excellent in more group B patients (Iomeprol 400) than group A patients (Iomeprol 300). There was an overall trend favouring Iomeprol 400 for this criterion. For the criterion evaluability of vessels in the portal venous phase there was no consistent trend with both readers.

For all criteria Reader 2 tended to assign more patients to lower categories than Reader 1.

The detailed results of the qualitative image assessment are summarized in Table 4Go.


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  		Table 4. Comparison of outcomes of dual-phase pancreatic multidetector CT according to the Iomeprol 300 and 400 protocols described in Table 1Go

 

   Discussion
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
References
 
Multislice CT allows the acquisition of multiple slices within subsecond rotation times and has led to an improvement of both temporal and spatial resolution in CT scanning. In MSCT of the pancreas, separate acquisition of defined perfusion phases has become standard. Yet to guarantee an optimum of contrast between physiological structures and pathologies, adaptation of the contrast material protocols to the higher scanning speed of MSCT is necessary.

Contrast enhancement after intravenous injection is determined by many interacting factors, e.g. type, volume and concentration of contrast medium, injection technique, tissue characteristics and patient characteristics such as age, sex, weight, height, cardiovascular status and renal function [7, 19–23]. For description of contrast medium enhancement of blood vessels and organs, mathematical compartment models have been developed based on physiological data and pharmacokinetic rules [20, 24]. According to these approaches, contrast medium enhancement of blood vessels follows the rules of a one-compartment model and depends on the volume of the blood vessel compartment, the flow rate within the vessel, the input contrast material concentration and the time [20]. For a description of contrast enhancement of organs, a two-compartment model must be applied that considers the intravascular and extracellular–extravascular space of the organs [20]. According to this model, organ enhancement is a result of enhancement of the intravascular and extracellular–extravascular spaces. Contrast enhancement of the extracellular–extravascular space depends on the concentration gradient between the intravascular and extracellular–extravascular spaces, the volume of the extracellular–extravascular space, the permeability of the organ microvasculature and cellular interfaces, and the surface area and time [20]. A high concentration gradient between the intravascular and extracellular–extravascular spaces allows a high influx of contrast material into the extracellular–extravascular space and contributes to high organ enhancement. Such a high concentration gradient can be achieved either by an increase of the contrast agent injection rate or by an increase of the contrast agent concentration [1, 4, 7, 15, 19].

In our study we focused on contrast agent concentration and investigated the influence of two different iodine concentrations (300 mg ml–1 vs 400 mg ml–1) on contrast enhancement in MSCT of the pancreas. The injection rate (5 ml s–1), the amount of iodine applied (39 g), and the injection technique were kept constant in both groups. The design of our study allowed us to eliminate statistically significant influences of the patient-related factors, age, sex, weight and height, on contrast enhancement. Differences in contrast material transit times (time from the cubital vein to the organ) and circulation times in our study patients were compensated for by the use of a test bolus technique. The efficacy of this technique has been proven by other investigators [17, 18, 25, 26].

As it is well known that flow characteristics of contrast agents are influenced by contrast agent viscosity and that the viscosity increases with iodine concentration and decreases with rising temperatures, we heated both contrast agents to 37°C before injection. At this temperature, viscosity remained different for the two contrast agents with 4.5 mPas for Iomeprol 300 and 12.6 mPas for Iomeprol 400. However the bolus tracking we performed did not show statistically significant differences in contrast bolus arrival time in the aorta at the region of the SMA. Therefore, we assume that as far as the flow characteristics of Iomeprol 300 and 400 in major arteries were concerned, the differences in contrast agent viscosity were of minor importance.

Several different helical CT scanning protocols have been described for pancreatic imaging [2, 3, 5, 6, 9–13]. Recently, pancreatic parenchymal phase imaging with a delay of about 35 s combined with portal venous phase imaging, has been recommended by McNulty because these two phases are associated with maximum tumour conspicuity, maximum opacification of the coeliac artery and SMA (pancreatic parenchymal phase), and maximum enhancement of the superior mesenteric and portal veins (portal venous phase) [11]. Early arterial phase imaging was considered necessary only for CT angiography in McNulty's study [11]. As the intention of our study was to investigate the effects of iodine concentration on CT angiography as well as on organ enhancement, we used a dual-phase scanning protocol with a delay of 17.02±4.41 s for the early arterial phase in order to maximize contrast in the mesenteric arteries and with a delay of 50–70 s for the portal venous phase in order to obtain maximum mesenteric and portal venous as well as hepatic enhancement and maximum tumour conspicuity.

Contrast enhancement measurements in our study revealed significantly higher enhancement of the aorta, coeliac trunk, SMA, pancreas, pancreatic carcinomas, spleen, kidneys, and wall of the small intestine in the arterial phase with an iodine concentration of 400 mg ml–1 compared with 300 mg ml–1. These results are supported by a recent study of Engeroff [4]: after injection of a non-ionic contrast agent with an iodine concentration of 370 mg ml–1 in one group and 300 mg ml–1 in a second group (amount of iodine 37 g, flow rate 4 ml s–1), the higher concentration led to a significantly higher arterial phase contrast enhancement of the aorta and the pancreas. To our knowledge, contrast enhancement studies of pancreatic masses, the kidneys and the wall of the small intestine comparing various iodine concentrations do not yet exist.

Higher contrast enhancement of arteries and organs with higher iodine concentrations during the arterial phase is not unexpected and can be explained by the aforementioned compartment models. With more highly concentrated contrast agents, more iodine is applied per time, thus leading to a higher concentration of contrast material in arteries. In organs such as the pancreas, kidneys, spleen and wall of the small intestine, there is a higher iodine concentration in the intravascular space with the higher iodine concentration; additionally, the higher intravascular/extracellular–extravascular concentration gradient with the higher iodine concentration leads to a higher iodine concentration in the extracellular–extravascular space. This explanation is possibly also applicable to pancreatic malignancies.

The effect of various iodine concentrations on contrast enhancement during the portal venous phase was also subject of Engeroff's recent study [4]. However, in contrast to our results, Engeroff did not identify significant differences in contrast enhancement for the pancreas during the portal venous phase. A possible explanation for this discrepancy concerning pancreatic enhancement is that the difference in the total amount of iodine injected per time between the compared study groups was lower in Engeroff's study than in ours (280 mg s–1 vs 500 mg s–1).

The higher enhancement of the portal vein with Iomeprol 400 than with Iomeprol 300 during the portal venous phase in our study was presumably caused by the more compact contrast bolus in group B compared with group A (98 ml vs 130 ml), that reached the portal vein during the portal venous phase.

Concerning the 11 pancreatic carcinomas of our study group, there were no statistically significant tumour-to-pancreatic parenchymal attenuation differences between the two groups (Iomeprol 300 vs Iomeprol 400) during the arterial phase as well as the portal venous phase. This can be explained by the fact that both the pancreatic carcinomas as well as the normal pancreatic parenchyma showed higher contrast enhancement with the higher iodine concentration during the arterial and portal venous phase. On the other hand side, the number of pancreatic carcinomas in our study was small, precluding a final judgement of the influence of Iomeprol 300 and 400 on tumour-to-pancreatic parenchymal attenuation differences in pancreatic carcinomas. For a reasonable statistical evaluation a higher number of pancreatic carcinomas must be investigated.

To investigate the clinical relevance of the contrast enhancement differences achieved by various iodine concentrations, our images were assessed qualitatively by two blinded independent readers.

This qualitative assessment revealed the superiority of the higher iodine concentration for the criteria technical quality and contribution of the contrast agent to the diagnostic value. The superiority of Iomeprol 400 for these criteria is presumably due to the generally greater contrast enhancement of the abovementioned vessels and organs in distinct perfusion phases with the higher iodine concentration and the consecutively higher contrast between certain organs, vessels and fatty tissue. If the higher contrast enhancement with the higher iodine concentration in organs such as the kidneys, spleen and small intestine, however, is diagnostically important and helps to verify the presence or absence of diseases was not the subject of this study and needs further investigation.

In accordance with the significantly higher contrast enhancement of arteries and the significantly higher attenuation difference between the aorta, the coeliac trunk, the SMA and the pancreatic carcinomas during the arterial phase with the higher iodine concentration, vessel evaluability in the arterial phase was considered better by both readers for Iomeprol 400.

Concerning vessel evaluability in the portal venous phase, the two readers could not find relevant differences between the two contrast agents for this criterion. This result is in accordance with the fact that there were no statistically significant attenuation differences between the large and small arteries and the pancreatic carcinomas and the portal vein and the pancreatic carcinomas during the portal venous phase between the two groups.

Concerning visualization of pancreatic tumours, the two readers did not regard the higher iodine concentration as superior for delineation between tumour and surrounding tissue and evaluability of organ infiltration adjacent to the pancreas. This result is in accordance with the not statistically different tumour-to-pancreatic parenchymal attenuation differences we calculated for both groups.

Concerning nephrotoxicity there is no significant difference in renal tolerance between the concentration of 300 mg ml–1 and 400 mg ml–1 in patients with normal renal function [27]. However, caution should be considered in patients with renal impairment as high concentration of contrast media might induce further reduction in renal function.

In summary, the higher iodine concentration leads to a higher arterial phase contrast enhancement of large and small arteries in MSCT of the pancreas and improves the evaluability of vessels in the arterial phase. Detection and demarcation of hypovascularized pancreatic carcinomas was not found to improve by the higher iodine concentration. However, for a final judgement a higher number of pancreatic tumours must be investigated.

Received for publication August 27, 2003. Revision received April 27, 2004. Accepted for publication June 8, 2004.


   References
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 

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