Detection of focal liver lesions: CT of the hepatobiliary system with gadoxetic acid disodium, or Gd-EOB-DTPA

Computed Tomography Cholangiography Using the Magnetic Resonance Contrast Agent Gadoxetate Disodium: A Phantom Study

OBJECTIVE

The purpose of this work is to determine whether low doses of gadoxetate disodium (Eovist; Bayer Healthcare LLC, Whippany, NJ), a gadolinium-based contrast agent used for magnetic resonance liver imaging, can be visualized for computed tomography (CT) cholangiography using a phantom setup.

MATERIALS AND METHODS

Vials containing 4 concentrations of gadoxetate disodium (1.9, 3.4, 4.8, and 9.6 mg Gd/mL) were placed in a 35 × 26-cm water phantom and imaged on 2 CT scanners: Siemens Somatom Flash and Force (Siemens Healthcare, Erlangen, Germany). These concentrations correspond to the estimated concentration in the bile duct for a 40-, 70-, or 100-kg patient, and twice the concentration of a 100-kg patient, respectively. Single-energy (SE) scans were acquired at 70, 80, 90, 100, 120, and 140 kVp, and dual-energy scans were acquired at 90/150Sn (Force) and 100/150 (Flash) for 2 dose levels (CTDIvol 13 and 23 mGy). Virtual monoenergetic images at 50 keV were created (Mono+; Siemens Healthcare, Erlangen, Germany). The mean intensity and standard deviation for each concentration of gadoxetate disodium and the water background were extracted from each image set and used to compute the contrast and contrast-to-noise ratio (CNR). To determine whether the signal provided by gadoxetate disodium was clinically sufficient, the measures were compared with those acquired from 12 clinical CT cholangiography examinations performed with iodine-containing iodipamide meglumine.

RESULTS

From the retrospective clinical cohort, mean contrast (± standard deviation) of 239 ± 107 HU and CNR of 12.8 ± 4.2 were found in the bile duct relative to the liver. Comparing these metrics to the gadoxetate disodium samples, the highest concentration (9.6 mg Gd/mL) surpassed these thresholds at all energy levels. The 4.8 mg Gd/mL had sufficient CNR in the Force, but not in the Flash. The 3.4 mg Gd/mL had clinically relevant CNR at low kV of SE (<100 kVp) and 50 keV of dual energy in the Force but was insufficient in the Flash. Images acquired by the Force had a lower noise level and greater CNR compared with the Flash. Similar trends were seen at both dose levels.

CONCLUSIONS

Gadoxetate disodium shows promise as a viable contrast agent for CT cholangiography, with CNR similar to those seen clinically with an iodine-based contrast agent. Dual-energy CT or low kV SE-CT is helpful to enhance the signal.

Hepatic computed tomography and cholangiography by use of gadoxetic acid in healthy cats

OBJECTIVE

To evaluate 3 doses of gadoxetic acid (Gd-EOB-DPTA) for hepatic CT and cholangiography in cats and to determine optimal timing for hepatobiliary image acquisition and evaluation of the contrast-enhanced hepatobiliary anatomy.

ANIMALS

6 healthy cats.

PROCEDURES

Cats were anesthetized; sequential CT scans were performed 0, 5, 25, 45, 65, and 85 minutes after IV administration of Gd-EOB-DTPA at low (0.0125 mmol/kg), medium (0.1 mmol/kg), and high (0.3 mmol/kg) doses. Hepatobiliary enhancement for each dose was objectively assessed over time and by use of a subjective semiquantitative visual assessment score.

RESULTS

No contrast-related adverse effects were detected. Each increase in dose of contrast medium resulted in a significant increase in HU across the hepatobiliary system. The liver had a significantly higher number of HU at 45 minutes, with homogenous enhancement at all doses of contrast medium. Contrast-enhanced cystic and bile duct HU were significantly higher and maximal at 65 minutes. Contrast-enhanced gallbladder HU did not plateau by 85 minutes. At a high dose of contrast medium, 12 of 60 (20%) biliary tract scores indicated no enhancement, 34 (57%) indicated poor enhancement, and 14 (23%) indicated moderate enhancement. No cat had excellent enhancement of the biliary tract at any dose.

CONCLUSIONS AND CLINICAL RELEVANCE

Gd-EOB-DTPA-enhanced hepatic CT and cholangiography in cats were safely performed and provided good hepatic enhancement but poor to moderate enhancement of the biliary tract. This technique may be useful for assessing the liver parenchyma in cats, but its value for assessing the biliary tract is questionable.

Technical Note: Evaluation of kV CBCT enhancement using a liver-specific contrast agent for stereotactic body radiation therapy image guidance

PURPOSE

To evaluate possible use for cone-beam computed tomography (CBCT) guidance, this phantom study evaluated the contrast enhancement provided by Gadoxetate Disodium (Primovist^® CAN/EU, or Eovist^® USA, Bayer Healthcare, Leverkusen, Germany), a contrast agent that is taken up selectively by liver cells and is retained for up to an hour. Image quality from CBCT was benchmarked against helical fan-beam computed tomography for two phantom geometries.

METHODS AND MATERIALS

Concentrations were diluted to 0.0125-0.1 mmol per kilogram of body weight (mmol/kg) corresponding to expected physiological concentrations in the liver. Kilovoltage CBCT imaging parameters of x-ray tube potential, current, and filtration were investigated using clinically available options on a TrueBeam STx linear accelerator CBCT platform. Two phantoms were created, a cylindrical idealized imaging geometry and an ellipsoidal more realistic abdominal geometry. All parameters were optimized according to the contrast-to-noise ratio (CNR) image quality metric, as a function of concentration, following the Rose criterion for CNR.

RESULTS

Acceptable CNR was defined as greater than or equal to three, in accordance with the Rose criterion for CNR. These were found in a range of expected liver concentrations of 0.025-0.1 mmol/kg for a tube potential of 100 kVp, half-fan bowtie filtration and tube currents giving exposures between 2025 and 5085 mAs. Linear correlations were found for all CNR as a function of concentration, in agreement with the literature.

CONCLUSION

Based on this phantom study, with appropriate selection of imaging protocol, Gadoxetate Disodium may provide useful liver CBCT enhancement at physiologically achievable liver concentrations.

Monte Carlo simulation-based approach to model the size distribution of metastatic tumors

The size distribution of metastatic tumors and its time evolution are traditionally described by integrodifferential equations and stochastic models. Here we develop a simple Monte Carlo approach in which each event of metastasis is treated as a chance event through random-number generation. We demonstrate the accuracy of this approach on a specific growth and metastasis model by showing that it quantitatively reproduces the size distribution and the total number of tumors as a function of time. The approach also yields statistical distribution of patient-to-patient variations, and has the flexibility to incorporate many real-life complexities.

Contrast agents: X-ray contrast agents and molecular imaging--a contradiction?

It is the purpose of this article to discuss whether and how X-ray contrast media may contribute to molecular imaging. X-ray contrast media are small molecules containing heavy elements, preferentially iodine. Modern CT allows precise, fast and reliable quantification of contrast media concentrations in large volumes with excellent spatial resolution throughout the body. The main disadvantage is the low contrast sensitivity requiring iodine concentrations of > or =0.5 mg/ml. Various approaches of the past and the present to specific contrast agents reflecting physiological, cellular or molecular processes are presented and options for the future are discussed.

Gadoxate Disodium

Gadoxate disodium [gadolinium EOB DTPA, Gd-EOB-DTPA, gadoxetic acid, Eovist injection, Primovist] is a hydrophilic paramagnetic contrast agent being developed by Schering AG for hepatobiliary magnetic resonance imaging. In April 2004, gadoxate disodium (Primovist) was approved in Sweden, the reference member state for the EU registration. Following the Swedish approval, Schering will initiate a mutual recognition procedure for the EU with approvals expected in most countries during 2004. Gadoxate disodium is in phase III clinical trials in the US and has completed phase III studies in Japan. Submissions for approval in Japan and other Asian countries are planned for 2004. Schering AG plans to launch Eovist in Japan in 2005. Schering AG acquired a worldwide, royalty-bearing licence to EPIX Medical's patents covering liver-enhancing agents such as Eovist injection. These included a European patent (222886) and the US patents (4,899,755 and 4,888,008) that EPIX Medical exclusively licensed from the Massachusetts General Hospital (MGH). The MGH patents, a part of EPIX's extensive intellectual property, also covered albumin-targeted agents such as MS 325 (AngioMARK). Schering AG formally withdrew from the opposition proceedings against EPIX's EU patent 222886 following its acquisition of EPIX's intellectual property. These EU and US patents were also non-exclusively licensed by EPIX Medical to Bracco in September 2001. Apart from covering Eovist (Schering AG), the EU patent also covered gadobenate dimeglumine (MultiHance Bracco). Following the licensing agreement, Bracco withdrew its opposition to the patents in Europe and Japan, and both EPIX Medical and Bracco settled their European patent dispute. In its 2002 Annual Report, Schering predicted that Eovist has the potential to reach peak sales of euro50 million, three years after launch--at the time, launch in Europe was anticipated in 2004, followed by launch in Japan in 2005. This is down from earlier predictions, made at an analyst presentation in Berlin in March 2002, when the company forecast the product to reach peak sales of euro100 million.

Tissue-specific MR contrast agents

The purpose of this review is to outline recent trends in contrast agent development for magnetic resonance imaging. Up to now, small molecular weight gadolinium chelates are the workhorse in contrast enhanced MRI. These first generation MR contrast agents distribute into the intravascular and interstitial space, thus allowing the evaluation of physiological parameters, such as the status or existence of the blood-brain-barrier or the renal function. Shortly after the first clinical use of paramagnetic metallochelates in 1983, compounds were suggested for liver imaging and enhancing a cardiac infarct. Meanwhile, liver specific contrast agents based on gadolinium, manganese or iron become reality. Dedicated blood pool agents will be available within the next years. These gadolinium or iron agents will be beneficial for longer lasting MRA procedures, such as cardiac imaging. Contrast enhanced lymphography after interstitial or intravenous injection will be another major step forward in diagnostic imaging. Metastatic involvement will be seen either after the injection of ultrasmall superparamagnetic iron oxides or dedicated gadolinium chelates. The accumulation of both compound classes is triggered by an uptake into macrophages. It is likely that similar agents will augment MRI of atheriosclerotic plaques, a systemic inflammatory disease of the arterial wall. Thrombus-specific agents based on small gadolinium labeled peptides are on the horizon. It is very obvious that the future of cardiovascular MRI will benefit from the development of new paramagnetic and superparamagnetic substances. The expectations for new tumor-, pathology- or receptor-specific agents are high. However, is not likely that such a compound will be available for daily routine MRI within the next decade.

Efficacy of the iodine-free computed tomography liver contrast agent, Dy-EOB-DTPA, in comparison with a conventional iodinated agent in normal and in tumor-bearing rabbits

RATIONALE AND OBJECTIVES

To investigate the efficacy of the new liver-specific x-ray contrast agent, Dy-EOB-DTPA, in rabbits with VX2 liver tumors by spiral computed tomography (CT) in comparison to iopromide.

MATERIALS AND METHODS

The time course of liver enhancement was determined in five groups of two normal anesthetized rabbits, which received intravenous injections of Dy-EOB-DTPA before anesthesia at a dose of 0.5 mmol/kg. Fifteen, 30, 45, 60, and 90 minutes after administration spiral CT images were obtained and the attenuation in the livers were determined. A second group of ten rabbits with implanted VX2 tumors received in a random crossover design either Dy-EOB-DTPA at a dose of 0.5 mmol/kg or, 1 day later, iopromide at a dose of 600 mg iodine/kg. CT images were obtained 60 minutes after Dy-EOB-DTPA administration and both in the arterial and portal-venous phases after iopromide injection. Three radiologists evaluated the images. The rabbits were killed, and their livers were investigated histologically for liver tumors.

RESULTS

In normal animals, 0.5 mmol/kg Dy-EOB-DTPA resulted in a liver enhancement of 30 HU during the whole observation period of 90 minutes. In tumor-bearing animals, histology revealed 14 implanted tumors of 3-20 mm diameter. Sixty-five percent of the tumors were below 10 mm. Dy-EOB-DTPA was able to detect 13 tumors (93%), iopromide 11 (79%) both in the arterial and in the portal-venous phase. The difference was statistically not significant. In plain CT, seven tumors (50%) were found (P < 0.01 vs iopromide and Dy-EOB-DTPA). One scar and two sites of necrosis were detected by each of the methods.

CONCLUSION

Dy-EOB-DTPA injection at a dose of 0.5 mmol/kg resulted in a long-lasting detectability of 93% of all implanted tumors versus 79% found with iopromide.

Dy-EOB-DTPA: tolerance and pharmacokinetics in healthy volunteers and preliminary liver imaging in patients

RATIONALE AND OBJECTIVES

To investigate the tolerance and pharmacokinetics of the new liver-specific x-ray contrast agent Dy-EOB-DTPA [(4S)-4-(4-ethoxybenzyl)-3,6,9-tris(carboxylatomethyl)-3,6,9-triazaundecanedioic acid, dysprosium (Dy) complex, disodium salt] in healthy volunteers and to obtain preliminary imaging data by abdominal spiral computed tomography (CT) in tumor patients with liver metastases.

METHODS

A total of 40 healthy male volunteers received 10-minute intravenous infusions of 0.05, 0.1, 0.25, 0.375, or 0.5 mmol/kg Dy-EOB-DTPA (n = 6 per dose group) or placebo (n = 10). Blood, urine, and feces were sampled for Dy measurements by inductively coupled plasma atomic emission spectrometry (ICP-AES) and for the detection of possible metabolites by high-performance liquid chromatography analysis with ICP-AES detection. Safety parameters were determined before, during, and after the study. Two patients with suspected liver metastases first received 120 mL of iopromide (300 mg iodine/mL; approximately 0.6 mmol/kg) and, 24 or 72 hours later, Dy-EOB-DTPA at a dose of 0.25 mmol/kg. Computed tomography images were obtained 50 seconds after iopromide administration and before and 90 minutes after Dy-EOB-DTPA administration.

RESULTS

Dysprosium-EOB-DTPA was well tolerated. At the higher doses (0.375 and 0.5 mmol/kg), there was a slight increase in side effect intensity. In general, nausea, headache, and paresthesia mainly were reported as mild to moderate adverse events. Laboratory parameters did not exceed the normal range. Electrocardiographic, vital sign, or hemodynamic parameters were not affected by contrast agent administration. The terminal half-life of elimination of Dy-EOB-DTPA was approximately 1.5 hours, total clearance was 2 to 3 mL x min(-1) x kg(-1), and the renal clearance was approximately 1.5 mL x min(-1) x kg(-1). There was a significant dose dependence for the following parameters: maximal concentration in blood, terminal half-life, mean residence time, total clearance, urinary excretion, and fecal excretion. The volume of distribution in the steady state and renal clearance were not dependent on dose. In the blood and urine, no metabolites of Dy-EOB-DTPA could be detected. In the tumor patients, CT scanning after Dy-EOB-DTPA injection increased the number of detected metastases from 27 (plain scan) to 40 (iopromide) and then to 41 (Dy-EOB-DTPA) in patient No. 1 and from 1 (plain scan and iopromide) to 3 (Dy-EOB-DTPA) in patient No. 2.

CONCLUSIONS

Dysprosium-EOB-DTPA was shown to be a well-tolerated liver-specific contrast agent. Its pharmacokinetic profile is characterized by a terminal half-life of approximately 1.5 hours. There are indications of saturation of liver uptake at the highest dose level of 0.5 mmol/kg. In comparison with plain scans and scans performed after iodinated contrast agent administration, Dy-EOB-DTPA seems to increase the number of detectable liver lesions.

In vitro model of the human liver parenchyma to study hepatotoxic side effects by Dy-EOB-DTPA

RATIONALE AND OBJECTIVES

In vivo studies have shown species-specific toxicity after application of the liver-specific contrast agent Dy-ethoxybenzyl (EOB)-DTPA. To predict species differences in the laboratory, an in vitro model of the liver was used to examine the divergent results.

METHODS

Rat, canine, porcine, and human hepatocytes were isolated and embedded between layers of collagen. During and after 48 hours of incubation with different concentrations of Dy-EOB-DTPA (maximum concentration 50 mmol/L), morphological changes and enzyme leakage were determined.

RESULTS

The response to the contrast agent varied for hepatocytes from different species. For canine cells, morphological changes and cell death were evident with as little as 5 mmol/L Dy-EOB-DTPA. Rat hepatocytes tolerated up to 50 mmol/L Dy-EOB-DTPA, and enzyme leakage was transient. Only after incubation with 50 mmol/L Dy-EOB-DTPA was the formation of intracellular vacuoles evident. In contrast, even the highest concentration of Dy-EOB-DTPA did not cause an enzyme leakage of porcine or human hepatocytes, although similar vacuoles were seen.

CONCLUSIONS

These data demonstrate a species-dependent toxicity for Dy-EOB-DTPA in vitro, with similar responses in porcine and human hepatocytes.

A dynamical model for the growth and size distribution of multiple metastatic tumors

Metastasis is the spread of tumors culminating in the establishment of one or more secondary tumors at remote sites. In deciding the best treatment for cancer therapy, estimations of the colony size of metastatic tumors and predictions of the future spread of colonies are needed. A dynamical model for the colony size distribution of multiple metastatic tumors is presented here. The dynamics is described by equations that incorporate both the colonization by metastasis and the growth of each colony. When the colony growth is subject to the Gompertz function, the explicit solution obtained tends to an asymptotic stable distribution that shows a monotonically decreasing or U-shaped pattern according to the values of clinically significant parameters, such as the colonization coefficient and the fractal dimension of blood vessels. This predicted colony size distribution agrees well with successive data of a clinically observed size distribution of multiple metastatic tumors of liver cancer. The combined analysis of the theoretical colony size distribution and clinical data will give useful information on the diagnosis and the therapy for cancer patients.

Delivery of diagnostic agents in computed tomography

Computed tomography is a reliable, widely available imaging modality with high spatial resolution. Except for trauma detection, in practically all cases contrast agents are administered for improving image quality. The presently available agents are nonspecific compounds with distribution in the extracellular space. Specificity (i.e. high contrast in selected tissues) is only possible when the pharmacokinetic behavior (peak levels at the region of the interest) is followed on a time scale which counts in seconds. If the peak time is missed, a second injection of contrast material is necessary. The objective of extensive research efforts have therefore been the search for tissue-specific contrast agents which should result both in higher and in longer lasting local concentrations. For the tissue targets, liver, spleen, lymph nodes and the blood pool, efficient contrast enhancing compounds have been described utilizing different active transport systems or passive diffusion-limiting molecular sizes. The agents include water-soluble metal chelates, iodinated polymeric compounds and contrast agent-carrying liposomes. The remaining task for the future will be to improve the tolerability of the contrast agents to such an extent that the side-effect incidence and severity is low enough to allow for the use of these agents in patients.

Pharmacokinetics of the liver-specific contrast agent Gd-EOB-DTPA in relation to contrast-enhanced liver imaging in humans

This study was performed to evaluate the effect of dose on the pharmacokinetics and efficacy of the gadolinium-based contrast medium gadoxetic acid, disodium, [gadolinium (4S)-4-(4-ethoxybenzyl)-3,6,9-tris(carboxylatomethyl)-3,6, 9-triazaundecandioic acid-disodium salt] (Gd-EOB-DTPA) as a liver-specific hepatobiliary contrast medium for computed tomography. Pharmacokinetics in serum and the pattern of elimination were investigated in 18 healthy volunteers up to 6 days after a 10-minute infusion of 0.2 mmol, 0.35 mmol, and 0.5 mmol of gadolinium per kilogram of body weight. Pharmacokinetic behavior was compared with the compute tomographic attenuation data in the liver parenchyma after the same doses in patients. Urinary and fecal excretion accounted for approximately equal portions of the administered dose. The degree of renal elimination increased with increasing doses, whereas renal clearance and half-life from urine data were not affected by dose. Dose-normalized area under the concentration-time curve was significantly increased with increasing doses indicating saturation in liver uptake for the highest dose. This finding was in agreement with the measured net increase in liver attenuation by computed tomography. Hepatic disposition revealed slight saturation phenomena for the highest dose (0.5 mmol gadolinium/kg). Nevertheless, this dose resulted in sufficient uptake by human liver, allowing for computed tomographic imaging.