Comparison of Gd-BOPTA with Gd-DTPA in MR imaging of rat liver

Facile Synthesis of Rigid Binuclear Manganese Complexes for Magnetic Resonance Angiography and SLC39A14-Mediated Hepatic Imaging

Manganese(II)-based contrast agents (MBCAs) are potential candidates for gadolinium-free enhanced magnetic resonance imaging (MRI). In this work, a rigid binuclear MBCA (Mn2-PhDTA2) with a zero-length linker was developed via facile synthetic routes, while the other dimer (Mn2-TPA-PhDTA2) with a longer rigid linker was also synthesized via more complex steps. Although the molecular weight of Mn2-PhDTA2 is lower than that of Mn2-TPA-PhDTA2, their T1 relaxivities are similar, being increased by over 71% compared to the mononuclear Mn-PhDTA. In the presence of serum albumin, the relaxivity of Mn2-PhDTA2 was slightly lower than that of Mn2-TPA-PhDTA2, possibly due to the lower affinity constant. The transmetalation reaction with copper(II) ions confirmed that Mn2-PhDTA2 has an ideal kinetic inertness with a dissociation half-life of approximately 10.4 h under physiological conditions. In the variable-temperature 17O NMR study, both Mn-PhDTA and Mn2-PhDTA2 demonstrated a similar estimated q close to 1, indicating the formation of monohydrated complexes with each manganese(II) ion. In addition, Mn2-PhDTA2 demonstrated a superior contrast enhancement to Mn-PhDTA in in vivo vascular and hepatic MRI and can be rapidly cleared through a dual hepatic and renal excretion pattern. The hepatic uptake mechanism of Mn2-PhDTA2 mediated by SLC39A14 was validated in cellular uptake studies.

Development of a Suite of Gadolinium-Free OATP1-Targeted Paramagnetic Probes for Liver MRI

Five amphiphilic, anionic Mn(II) complexes were synthesized as contrast agents targeted to organic anion transporting polypeptide transporters (OATP) for liver magnetic resonance imaging (MRI). The Mn(II) complexes are synthesized in three steps, each from the commercially available trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) chelator, with T1-relaxivity of complexes ranging between 2.3 and 3.0 mM-1 s-1 in phosphate buffered saline at an applied field strength of 3.0 T. Pharmacokinetics were assessed in female BALB/c mice by acquiring T1-weighted images dynamically for 70 min after agent administration and determining contrast enhancement and washout in various organs. Uptake of Mn(II) complexes in human OATPs was investigated through in vitro assays using MDA-MB-231 cells engineered to express either OATP1B1 or OATP1B3 isoforms. Our study introduces a new class of Mn-based OATP-targeted contrast that can be broadly tuned via simple synthetic protocols.

Organic Anion Transporting Polypeptide 1B1 Is a Potential Reporter for Dual MR and Optical Imaging

Membrane proteins responsible for transporting magnetic resonance (MR) and fluorescent contrast agents are of particular importance because they are potential reporter proteins in noninvasive molecular imaging. Gadobenate dimeglumine (Gd-BOPTA), a liver-specific MR contrast agent, has been used globally for more than 10 years. However, the corresponding molecular transportation mechanism has not been validated. We previously reported that the organic anion transporting polypeptide (OATP) 1B3 has an uptake capability for both MR agents (Gd-EOB-DTPA) and indocyanine green (ICG), a clinically available near-infrared (NIR) fluorescent dye. This study further evaluated OATP1B1, another polypeptide of the OATP family, to determine its reporter capability. In the OATP1B1 transfected 293T transient expression model, both Gd-BOPTA and Gd-EOB-DTPA uptake were confirmed through 1.5 T MR imaging. In the constant OAPT1B1 and OATP1B3 expression model in the HT-1080 cell line, both HT-1080-OAPT1B1 and HT-1080-OATP1B3 were observed to ingest Gd-BOPTA and Gd-EOB-DTPA. Lastly, we validated the ICG uptake capability of both OATP1B1 and OATP1B3. OAPT1B3 exhibited a superior ICG uptake capability to that of OAPT1B1. We conclude that OATP1B1 is a potential reporter for dual MR and NIR fluorescent molecular imaging, especially in conjunction with Gd-BOPTA.

AP-1 subunits converge promiscuously at enhancers to potentiate transcription

The AP-1 transcription factor (TF) dimer contributes to many biological processes and environmental responses. AP-1 can be composed of many interchangeable subunits. Unambiguously determining the binding locations of these subunits in the human genome is challenging because of variable antibody specificity and affinity. Here, we definitively establish the genome-wide binding patterns of five AP-1 subunits by using CRISPR to introduce a common antibody tag on each subunit. We find limited evidence for strong dimerization preferences between subunits at steady state and find that, under a stimulus, dimerization patterns reflect changes in the transcriptome. Further, our analysis suggests that canonical AP-1 motifs indiscriminately recruit all AP-1 subunits to genomic sites, which we term AP-1 hotspots. We find that AP-1 hotspots are predictive of cell type–specific gene expression and of genomic responses to glucocorticoid signaling (more so than super-enhancers) and are significantly enriched in disease-associated genetic variants. Together, these results support a model where promiscuous binding of many AP-1 subunits to the same genomic location play a key role in regulating cell type–specific gene expression and environmental responses.

Synthesis and Evaluation of Manganese(II)-Based Ethylenediaminetetraacetic Acid-Ethoxybenzyl Conjugate as a Highly Stable Hepatobiliary Magnetic Resonance Imaging Contrast Agent

In this study, we designed and synthesized a highly stable manganese (Mn²⁺)-based hepatobiliary complex by tethering an ethoxybenzyl (EOB) moiety with an ethylenediaminetetraacetic acid (EDTA) coordination cage as an alternative to the well-established hepatobiliary gadolinium (Gd³⁺) chelates and evaluated its usage as a T₁ hepatobiliary magnetic resonance imaging (MRI) contrast agent (CA). This new complex exhibits higher r₁ relaxivity (2.3 mM^-1 s^-1) than clinically approved Mn²⁺-based hepatobiliary complex Mn-DPDP (1.6 mM^-1 s^-1) at 1.5 T. Mn-EDTA-EOB shows much higher kinetic inertness than that of clinically approved Gd³⁺-based hepatobiliary MRI CAs, such as Gd-DTPA-EOB and Gd-BOPTA. In addition, in vivo biodistribution and MRI enhancement patterns of this new Mn²⁺ chelate are comparable to those of Gd³⁺-based hepatobiliary MRI CAs. The diagnostic efficacy of the new complex was demonstrated by its enhanced tumor detection sensitivity in a liver cancer model using in vivo MRI.

Historical Perspective of Imaging Contrast Agents

Contrast agents were introduced early in the history of medical imaging. Iodine-based intravascular agents became the radiographic compounds of choice and refinements of their chemical structures led to the highly tolerated low-osmolarity agents in use today. Gadolinium became the most popular compound for MR imaging; however, recognition of nephrogenic systemic fibrosis and in vivo dechelation intensified research on their safety profile. Ultrasonography contrast media evolved from manual injections of air through agitated saline solutions to microbubbles with different gases. Research has concentrated on bubble stabilization and development of small but sufficiently echogenic particles.

A relaxometric method for the assessment of intestinal permeability based on the oral administration of gadolinium-based MRI contrast agents

Herein, a new relaxometric method for the assessment of intestinal permeability based on the oral administration of clinically approved gadolinium (Gd)-based MRI contrast agents (CAs) is proposed. The fast, easily performed and cheap measurement of the longitudinal water proton relaxation rate (R1) in urine reports the amount of paramagnetic probe that has escaped the gastrointestinal tract. The proposed method appears to be a compelling alternative to the available methods for the assessment of intestinal permeability. The method was tested on the murine model of dextran sulfate sodium (DSS)-induced colitis in comparison with healthy mice. Three CAs were tested, namely ProHance®, MultiHance® and Magnevist®. Urine was collected for 24 h after the oral ingestion of the Gd-containing CA at day 3-4 (severe damage stage) and day 8-9 (recovery stage) after treatment with DSS. The Gd content in urine measured by (1)H relaxometry was confirmed by inductively coupled plasma-mass spectrometry (ICP-MS). The extent of urinary excretion was given as a percentage of excreted Gd over the total ingested dose. The method was validated by comparing the results obtained with the established methodology based on the lactulose/mannitol and sucralose tests. For ProHance and Magnevist, the excreted amounts in the severe stage of damage were 2.5-3 times higher than in control mice. At the recovery stage, no significant differences were observed with respect to healthy mice. Overall, a very good correlation with the lactulose/mannitol and sucralose results was obtained. In the case of MultiHance, the percentage of excreted Gd complex was not significantly different from that of control mice in either the severe or recovery stages. The difference from ProHance and Magnevist was explained on the basis of the (known) partial biliary excretion of MultiHance in mice.

Gadolinium-containing magnetic resonance contrast media: investigation on the possible transchelation of Gd³⁺ to the glycosaminoglycan heparin

Retention of gadolinium (Gd) in biological tissues is considered an important cofactor in the development of nephrogenic systemic fibrosis (NSF). Research on this issue has so far focused on the stability of Gd-based contrast media (GdCM) and a possible release of Gd³⁺ from the complex. No studies have investigated competing chelators that may occur in vivo. We performed proton T(1) -relaxometry in solutions of nine approved GdCM and the macromolecular chelator heparin (250 000 IU per 10 ml) without and with addition of ZnCl₂. For the three linear, nonspecific GdCM complexes, Omniscan®, OptiMARK® and Magnevist®, 2 h of incubation in heparin at 37 °C in the presence of 2.0 mm ZnCl₂ led to an increase in T₁-relaxivity by a factor of 7.7, 5.6 and 5.1, respectively. For the three macrocyclic complexes, Gadovist®, Dotarem® and Prohance®, only a minor increase in T₁-relaxivity by a factor of 1.5, 1.6 and 1.7 was found, respectively. Without addition of ZnCl₂, no difference between the two GdCM groups was observed (factors of 1.4, 1.2, 1.1, 1.3, 1.5 and 1.4, respectively). The increase in T₁-relaxivities observed for linear GdCM complexes may be attributable to partial transchelation with formation of a macromolecular Gd-heparin complex. For comparison, mixing of GdCl₃ and heparin results in a 8.7-fold higher T₁-relaxivity compared with a solution of GdCl₃ in water. Heparin is a glycosaminoglycan (GAG) and as such occurs in the human body as a component of the extracellular matrix. GAGs generally are known to be strong chelators. Gd³⁺ released from chelates of GdCM might be complexed by GAGs in vivo, which would explain their retention in biological tissues. Plasma GAG levels are elevated in end-stage renal disease; hence, our results might contribute to the elucidation of NSF.

A historical overview of magnetic resonance imaging, focusing on technological innovations

Magnetic resonance imaging (MRI) has now been used clinically for more than 30 years. Today, MRI serves as the primary diagnostic modality for many clinical problems. In this article, historical developments in the field of MRI will be discussed with a focus on technological innovations. Topics include the initial discoveries in nuclear magnetic resonance that allowed for the advent of MRI as well as the development of whole-body, high field strength, and open MRI systems. Dedicated imaging coils, basic pulse sequences, contrast-enhanced, and functional imaging techniques will also be discussed in a historical context. This article describes important technological innovations in the field of MRI, together with their clinical applicability today, providing critical insights into future developments.

Hepatic hemangioma and metastasis: differentiation with gadoxetate disodium-enhanced 3-T MRI

OBJECTIVE

The purpose of this study was to evaluate the gadoxetate disodium-enhanced MRI findings of hepatic hemangioma and to investigate the diagnostic performance in differentiating hepatic hemangioma and metastasis.

MATERIALS AND METHODS

Images of 32 hepatic hemangiomas in 25 patients and of 29 hepatic metastatic lesions in 20 patients were retrospectively reviewed. Two independent readers interpreted hepatobiliary phase images alone, dynamic extracellular phase images alone, and combined hepatobiliary and dynamic extracellular phase images. MRI findings and performance with respect to the differential diagnosis of hemangioma and metastasis were assessed.

RESULTS

During the hepatic arterial phase, 11 of the 32 hemangiomas (34%) exhibited early total enhancement, and nine (28%) exhibited peripheral nodular enhancement. A bright dot sign or minimal peripheral enhancement during the late dynamic phase was observed for a small number of lesions (6% and 28%, respectively). Twenty-three of the 29 metastatic lesions (79%) exhibited ring enhancement during the hepatic arterial phase. Twenty-nine hemangiomas (91%) and all of the metastatic lesions exhibited homogeneous or heterogeneous hypointensity during the hepatobiliary phase. The sensitivity, specificity, and area under the receiver operating characteristic curve for the detection of hemangioma were 76%, 81%, and 0.87 for the hepatobiliary phase alone; 97%, 88%, and 0.97 for the dynamic extracellular phase alone; and 97%, 88%, and 0.98 for the combination. Five nodules smaller than 1 cm (four hemangiomas, one metastatic lesion) that exhibited no enhancement during the arterial phase and minimal enhancement during the late dynamic phase were not differentiated.

CONCLUSION

Gadoxetate disodium-enhanced MRI was found useful for differentiating hepatic hemangiomas and metastatic lesions, especially during the dynamic extracellular phase. Only a limited number of lesions smaller than 1 cm in diameter, which exhibited minimal enhancement on late dynamic phase images, were difficult to diagnose.

MR contrast agents for liver imaging: what, when, how

The major classes of contrast agents currently used for magnetic resonance (MR) imaging of the liver include extracellular agents (eg, low-molecular-weight gadolinium chelates), reticuloendothelial agents (eg, ferumoxides), hepatobiliary agents (eg, mangafodipir), blood pool agents, and combined agents. Mechanisms of action, dosage, elimination, toxic effects, indications for use, and MR imaging technical considerations vary according to class. Gadolinium chelates are the most widely used. Ferumoxides are a useful adjunct for detection of hepatocellular carcinoma, particularly when used in combination with gadolinium to achieve improved lesion-to-liver contrast over that achievable with gadolinium alone. Mangafodipir is a prototype hepatobiliary agent that is taken up by lesions with functioning hepatocytes. It may be used for MR cholangiography as well as liver imaging. Although mangafodipir is no longer commercially available in the United States, it is currently marketed and used in Europe. Blood pool agents have not yet been approved for human use in the United States. However, a new combined MR contrast agent, gadobenate dimeglumine, recently was approved, and other agents are in various stages of development.

Fast Water-Exchange Gd3+-(DO3A-like) Complex Functionalized with Aza-15-Crown-5 Showing Prolonged Residence Lifetime in Vivo

A bis-hydrated Gd3+ complex based on tris acetic acid-1,4,7,10-tetraazacyclododecane (DO3A) that was functionalized with aza-15-crown-5 demonstrated a nearly optimal water-exchanging rate (k(ex) = 3.1 x 10(7) s(-1)) and low acute cytotoxicity. Efficient magnetic resonance signal intensity enhancements and prolonged residence lifetime induced by this small molecular complex in vivo were demonstrated even with one-fifth of the standard dosage used in the clinic.

Comparison of Gadolinium-BOPTA and Ferucarbotran-Enhanced Three-Dimensional T1-Weighted Dynamic Liver Magnetic Resonance Imaging in the Same Patient

OBJECTIVES

We sought to compare signal changes using Ferucarbotran and gadobenate dimeglumine (Gd-BOPTA) in dynamic 3D T1-weighted (T1w) GRE imaging of the liver.

MATERIAL AND METHODS

Thirty patients were prospectively included in the study. All patients underwent 2 high-field magnetic resonance (MR) examinations: first with Gd-BOPTA (Gd) and then after a mean interval of 4 days with ferucarbotran (Feru). Dynamic MRI was obtained with a 3D T1w GRE sequence (TR 6.33, TE 2.31, flip angle 20 degrees ). Contrast enhanced scans were assessed before intravenous injection of the contrast agent (precontrast), and postcontrast during the arterial phase (30 seconds), portal venous phase (60 seconds), and equilibrium phase (120 seconds). The signal intensities (SIs) of liver, spleen, aorta, and portal vein were defined by region of interest measurements. Signal intensity changes (SICs) and percentage signal intensity change (PSIC) were calculated using the formulas SIC=(SI pre - SI post)/SI pre and PSIC=SIC x 100%.

RESULTS

Positive signal enhancement was observed after intravenous injection of Feru during all dynamic measurements, whereas the mean SI values were lower compared with Gd. During the portal venous phase the mean SI of Gd was up to a factor of 2.1 higher (portal vein). The widest difference of SIC was observed during the equilibrium phase for liver parenchyma (Gd, 1.03; Feru, 0.24). The dynamic signal courses were similar for liver, portal vein and aorta. Different signal courses were obtained for the spleen.

CONCLUSIONS

Feru-enhanced T1w dynamic images demonstrated significant signal increases for liver, vessels, and spleen but overall lower signal intensities than Gd-BOPTA. The dynamic signal courses of ferucarbotran were similar to that of Gd-BOPTA during ll perfusion phases except in the spleen. Thus, it may be possible to detect typical enhancement pattern of focal liver lesions with Feru-enhanced dynamic T1w MRI.

Kinetics of gadobenate dimeglumine in isolated perfused rat liver: MR imaging evaluation

PURPOSE

To compare in the entire liver, the hepatic kinetics of gadobenate dimeglumine (Gd-BOPTA) and gadopentetate dimeglumine (Gd-DTPA) and to evaluate the hepatic transport of Gd-BOPTA.

MATERIALS AND METHODS

The authors studied both contrast agents in isolated perfused rat livers by measuring the magnetic resonance (MR) signal intensity (SI) in 12 rats, as well as the gadolinium concentrations in hepatic tissues in 42 rats. The intrahepatic transport of Gd-BOPTA was investigated with pharmacologic antagonism by using bromosulfophthalein. MR imaging was performed at 1.5 T with a fast gradient-echo T1-weighted MR sequence.

RESULTS

The hepatic kinetics based on the MR SI measured over time showed a rapid steady state during Gd-DTPA perfusion, while the SI continuously increased during the 30-minute Gd-BOPTA perfusion period. The pharmacokinetic modeling indicated that the half-lives of Gd-DTPA entry and exit were identical (mean, 1.3 minutes +/- 0.9 [standard error of mean]) and shorter than those observed with Gd-BOPTA (P <.001). The uptake of Gd-BOPTA was faster (mean half-life, 4.8 minutes +/- 0.3) than the washout (mean half-life, 17.5 minutes +/- 2.8) (P =.001). The combined perfusion of bromosulfophthalein and Gd-BOPTA decreased the SI enhancement in comparison with the perfusion of Gd-BOPTA alone (mean, 0.56 +/- 0.03 vs 2.54 +/- 0.39, P <.001). The entry and exit kinetic parameters obtained during the perfusion of Gd-BOPTA plus bromosulfophthalein were identical and comparable to those obtained during Gd-DTPA perfusion (P =.95). Acute bile duct ligation did not interfere with the uptake of Gd-BOPTA in hepatocytes, but it slowed down the excretion by approximately 50%. Measurements of gadolinium concentrations in hepatic tissues confirmed these findings.

CONCLUSION

In the liver, the hepatospecific contrast agent Gd-BOPTA enters into hepatocytes likely through the organic anion transporting peptide 1.

Detection of liver metastases: comparison of gadobenate dimeglumine-enhanced and ferumoxides-enhanced MR imaging examinations

PURPOSE

To compare gadobenate dimeglumine (Gd-BOPTA)-enhanced magnetic resonance (MR) imaging with ferumoxides-enhanced MR imaging for detection of liver metastases.

MATERIALS AND METHODS

Twenty consecutive patients known to have malignancy and suspected of having focal liver lesions at ultrasonography (US) underwent 1.0-T MR imaging with gradient-recalled-echo T1-weighted breath-hold sequences before, immediately after, and 60 minutes after Gd-BOPTA injection. Subsequently, MR imaging was performed with turbo spin-echo short inversion time inversion-recovery T2-weighted sequences before and 60 minutes after ferumoxides administration. All patients subsequently underwent intraoperative US within 15 days, and histopathologic analysis of their resected lesion-containing specimens was performed. Separate qualitative analyses were performed to assess lesion detection with each contrast agent. Quantitative analyses were performed by measuring signal-to-noise and contrast-to-noise ratios (CNRs) on pre- and postcontrast Gd-BOPTA and ferumoxides MR images. Statistical analyses were performed with Wilcoxon signed rank and Monte Carlo tests.

RESULTS

Sensitivity of ferumoxides-enhanced MR imaging was superior to that of Gd-BOPTA-enhanced MR imaging for liver metastasis detection (P <.05). Ferumoxides MR images depicted 36 (97%) of 37 metastases detected at intraoperative US, whereas Gd-BOPTA MR images depicted 30 (81%) metastases during delayed phase and 20 (54%) during dynamic phase. All six metastases identified only at ferumoxides-enhanced MR imaging were 5-10 mm in diameter. There was a significant increase in CNR between the lesion and liver before and after ferumoxides administration (from 3.8 to 6.8, P <.001) but not before or after Gd-BOPTA injection (from -4.8 to -5.5, P >.05).

CONCLUSION

Ferumoxides-enhanced MR imaging seems to be superior to Gd-BOPTA-enhanced MR imaging for liver metastasis detection.

Phase II double-blind, dose-ranging clinical evaluation of gadobenate dimeglumine in focal liver lesions: with analysis of liver and kidney signal change on early and delayed imaging

To evaluate the effect of contrast dose using gadobenate dimeglumine, 30 patients with focal liver lesions documented by computed tomography or ultrasound were studied by magnetic resonance imaging at 1.5 T. Patients received one of four doses of gadobenate dimeglumine (0.025, 0.05, 0.1, or 0.2 mmol/kg) or saline. The order of dosage was randomized, with both the physician and patient blinded to the administered dose. Scans were obtained before, immediately following injection, and after 80 minutes of delay. Enhancement effects were quantified by region of interest measurements. Films were also reviewed in a randomized prospective fashion by an abdominal radiologist blinded to contrast dose and diagnosis. Higher doses led to a statistically significant improvement in enhancement of normal liver, both on immediate (P = 0.01 for the comparison of 0.1 and 0.2 mmol/kg immediately post-contrast) and delayed scans (P = 0.003 for the same comparison). Liver-lesion contrast-to-noise ratio also increased with dose, although results for most comparisons by dose were not statistically significant. Scans following gadobenate dimeglumine injection were judged to provide additional diagnostic confidence sufficient to affect patient management in 10 of 24 cases. In seven cases this information was provided by dynamic scans, in one case by delayed scans, and in two cases by both dynamic and delayed scans. In 2 of the 10 cases the dose was 0.025 mmol/kg, in 2 cases 0.05 mmol/kg, in 3 cases 0.1 mmol/kg, and in 3 cases 0.2 mmol/kg. Gadobenate dimeglumine is effective for imaging of focal liver lesions at a range of doses, with trends toward improved diagnostic information at higher doses.

Delayed MR imaging of hepatocellular carcinoma enhanced by gadobenate dimeglumine (Gd-BOPTA)

The purpose of this study was to determine the efficacy of gadobenate dimeglumine (Gd-BOPTA)-enhanced magnetic resonance (MR) imaging for evaluation of hepatocellular carcinoma HCC. MR images were obtained in 14 patients with 31 HCC nodules as a part of a phase III clinical trial. T1- and T2-weighted images were obtained before and after iv administration of 0.1 mmol/kg of Gd-BOPTA. Two blinded readers evaluated pre- and delayed postcontrast images separately for detection of tumor nodules. Quantitative measurements of signal-to-noise (SNR) and tumor/liver contrast-to-noise (CNR) ratios were also performed. A signal/intensity ratio was calculated. Tumor enhancement was correlated with histologic findings. Consensus agreement of precontrast T1- and T2-weighted images revealed 23/31 HCC nodules in 14 patients; postcontrast T1-weighted images demonstrated 24/31 HCC nodules in the same number of patients. Combining both pre- and postcontrast images, 27/31 lesions were detected. Four patients had four well-differentiated HCC nodules detected only on postcontrast images, while three well-differentiated lesions in two patients were only seen on precontrast images. Quantitative evaluation showed an SNR ratio increase in both liver parenchyma and HCC nodules, as well as a significant increase in the absolute CNR ratio on postcontrast T1-weighted gradient-recalled images (P < 0.05). Well-differentiated HCC lesions showed a greater enhancement than poorly differentiated HCC lesions.

Delivery of diagnostic agents for magnetic resonance imaging

A review of contrast agents used for magnetic resonance imaging was made with regard to methods of drug delivery using published literature. Since the clinical approval of Gd-DTPA in 1988, there has been extensive research towards developing organ- and tissue-specific contrast agents. Targeting strategies have consistently improved along with improvements in nuclear medicine imaging, and a broad spectrum of potential agents has accumulated. Liver, blood-pool targeted, and, due to their inherent convenience of delivery, intraorally administered gastrointestinal agents have been developed or are being developed. For intravenous contrast agents, collective magnetic labels with modifications for some specificities results in the larger-sized agents which can be an obstacle for the agent in accessing the targeted cells. In conclusion, the next step in the development of specific contrast agents for clinical use is to improve non-specific delivery to the extra-capillary space adjacent to targeted cells.

Optimal dose of hepatobiliary contrast agent for MR cholangiography: experimental study in rats

The purpose of this study is to clarify the optimal dose of gadolinium-ethoxybenzyl-diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) for cholangiography in conventional T1-weighted imaging. We divided 30 rats into three dose groups (3, 10, and 30 micromol/kg). For the in vitro study, we collected bile and measured the concentration of gadolinium in bile after Gd-EOB-DTPA injection. T1-weighted images of the collected bile were obtained for measurement of signal intensity. For the in vivo study, we obtained T1-weighted images before and after injection and evaluated bile duct/liver contrast by the signal intensity ratio and visual assessment of the images. The gadolinium concentration had an early peak; however, the signal intensity of the bile had a later peak because of the high gadolinium concentration during the early phase, which induced a T2-shortening effect. Optimal bile duct/liver contrast was obtained in the 10-micromol/kg groups at all time points. We conclude that the optimal dose of Gd-EOB-DTPA for MR cholangiography in rats is 10 micromol/kg, one-third of the dose used in liver imaging.

Gadobenate dimeglumine (BOPTA) enhanced MR imaging: patterns of enhancement in normal liver and cirrhosis

To determine whether gadobenate dimeglumine (BOPTA) will adequately enhance cirrhotic liver parenchyma, and to document the enhancement patterns in cirrhosis, 14 cirrhotic and 20 non-cirrhotic patients were evaluated before and 60-120 minutes after gadolinium-BOPTA. Proof of liver cirrhosis was biopsy (6), surgical resection (3), and clinical follow-up (5). Enhancement effects were compared quantitatively by determining the liver signal-to-noise ratio (SNR) and signal enhancement in both populations. Qualitatively assessment of the liver enhancement was performed and classified as homogeneous or heterogeneous. Quantitative analysis: cirrhotic liver parenchyma presented a higher increase in SNR values, relative to non-cirrhotic liver parenchyma, on postcontrast images. Likewise the signal enhancement of cirrhotic liver parenchyma was superior to non-cirrhotic liver on T1-weighted SE images (P = .02) and in-phase GRE images (P < .001). There was no statistical difference on out-of-phase GRE images. Qualitative analysis: on T1-weighted SE postcontrast images, cirrhotic liver parenchyma showed a homogeneous enhancement in 7 patients and heterogeneous in 7. Whereas on GRE images, cirrhotic parenchyma showed heterogeneous enhancement in 9 patients and homogeneous in 5 patients. The heterogeneous enhancement was due to the presence of hypointense nodules in 7 patients and hyperintense nodules in 2 patients. In conclusion, our study has shown that the hepatobiliary contrast agent Gd-BOPTA is effective in the cirrhotic liver, demonstrating an increased liver enhancement compared with non-cirrhotic patients.

Detectability of small liver metastases with gadolinium BOPTA

RATIONALE AND OBJECTIVES

The ability to detect small liver metastases was evaluated with both gadolinium Gd BOPTA and Gd HP-DO3A on high-field (1.5 tesla [T]) magnetic resonance (MR) imaging using a rabbit tumor model.

METHODS

Five New Zealand White rabbits with metastatic liver disease (VX-2 adenocarcinoma) were imaged on a 1.5 T Siemens Vision MR system. Magnetic resonance studies were obtained in each animal on days 8 and 9 after tumor implantation. Each animal was studied twice, once after injection of 0.3 mmol/kg Gd HP-DO3A (gadoteridol or ProHance) and once after injection of 0.1 mmol/kg Gd BOPTA (gadobenate dimeglumine or MultiHance). The order of injection for the two agents was randomized with the two studies in any one animal separated by 24 hours to allow for clearance. Magnetic resonance image acquisition was performed in all cases with suspended respiration. Baseline two-dimensional FLASH T1-weighted and turbo-spin echo T2-weighted scans were acquired first. The contrast was then administered as an intravenous bolus. T1-weighted scans were acquired at 1, 5, 15, 30, 45, and 60 minutes after administration of Gd BOPTA and 1, 5, and 15 minutes after administration of Gd HP-DO3A. Each rabbit was killed after completion of imaging, their liver removed and taken to the veterinarian at the University's animal disease diagnostic laboratory for lesion confirmation.

RESULTS

Despite acquisition of precontrast T2-weighted scans, lesions could not be identified with certainty in four of five animals in the Gd HP-DO3A study. Normal liver signal intensity increased from 895 +/- 17 to a peak of 1384 +/- 50 at 1 minute after Gd HP-DO3A administration. After Gd BOPTA administration, normal liver signal intensity increased from 899 +/- 105 to a peak of 1433 +/- 76 at 15 minutes. Liver enhancement thereafter decreased gradually to 1297 +/- 84 at 60 minutes. The injection of 0.3 mmol/kg Gd HP-DO3A resulted in parenchymal enhancement, which was statistically superior (P < 0.01) to an injection of 0.1 mmol/kg Gd BOPTA at 1 minute, not statistically different at 5 minutes, and inferior (P < 0.02) at 15 minutes. From region of interest measurements, lesion detectability was statistically superior on scans at 15 to 60 minutes after Gd BOPTA administration compared with precontrast T1- and T2-weighted scans (P values: < 0.03- < 0.005). Lesion detectability was maximum at 30 minutes postcontrast (15.2 +/- 4.5), markedly superior to that precontrast on both T1- (5.7 +/- 5.0) and T2-weighted scans (7.2 +/- 1.5). On masked film review of the Gd BOPTA case set, no lesions were noted prospectively on T2-weighted scans. Lesions in all five animals were well visualized on scans 45 to 60 minutes after Gd BOPTA administration. The Gd HP-DO3A case set was not read masked, as lesions could be identified only in one of the five animals with all films available for inspection. An additional feature of scans with Gd BOPTA (used at a dose of 0.1 mmol/kg), in distinction to those with Gd HP-DO3A (used at a dose of 0.3 mmol/kg), was the diminished enhancement of hepatic vessels.

CONCLUSIONS

Using a rabbit model, small metastatic lesions (diameter, 2-4 mm) were well visualized on delayed postcontrast Gd BOPTA scans. These lesions could not be diagnosed prospectively on T2-weighted images. In only one of five animals were lesions detected on early dynamic post-contrast high-dose Gd HP-DO3A scans.

Ex-vivo MR imaging of liver intracellular contrast agents

The objective is to evaluate whether an ex-vivo model can be used to test intracellular contrast agents for MR imaging of the liver. T1 weighted inversion recovery, proton density spin echo and T2* weighted gradient echo images of the liver were acquired at 0.5 T in 10 rats before and 30 min after intravenous injection of 0.075 mmol/kg Gadolinium benzyloxypropionictetraacetate (Gd-BOPTA, n = 5) or 0.015 mmol/kg dextran magnetite (DM, n = 5), Four additional animals served as controls. After exsanguination and perfusion with saline and formalin, specimens of the liver and brain were embedded in an agar gel and examined with MR imaging one to three weeks later using the same protocol. In-vivo, the mean liver signal enhancement caused by Gd-BOPTA in T1, proton density and T2* weighted images was +23%, +28% and -70%, respectively. The mean liver signal enhancement caused by DM was -71%, -76% and -94%. In-vitro, no signal change was seen in the brain of animals injected with Gd-BOPTA and DM as compared to controls. Liver signal was increased by Gd-BOPTA and decreased by DM. Mean liver enhancement rate induced by Gd-BOPTA was +22%, +5% and +27% for T1, proton density and T2* weighted images, respectively. Mean liver enhancement rate induced by DM was -27%, -19% and -31%. MR imaging signal changes induced by liver intracellular contrast agents are still appreciable in an ex-vivo model. The latter might be useful for for preliminary investigation of intracellular contrast agents for MR imaging of the liver.

Contrast-enhanced MR imaging of the liver: comparison between Gd-BOPTA and Mangafodipir

The purpose of the study was to evaluate the MR contrast agents gadolinium benzyloxypropionictetro-acetate (Gd-BOPTA) and Mangafodipir for liver enhancement and the lesion-liver contrast on T1W spin-echo (SE) and gradient-recalled-echo (GRE) images. Fifty-one patients (three groups of 17 patients each) with known or suspected liver lesions were evaluated with T1W SE (300/12) and GRE (77-80/2.3-2.5/80 degrees) images before and after intravenous (IV) Gd-BOPTA (0.1 or 0.05 mmol/kg) or Mangafodipir (5 mumol/kg) in phase II to III clinical trials. Quantitative analysis by calculating liver signal-to-noise ratio (SNR), lesion-liver contrast-to-noise ratio (CNR), and spleen-liver CNR was performed. Liver SNR and spleen-liver CNR were always significantly increased postcontrast. SNR was highest after application of 0.1 mmol/kg Gd-BOPTA (51.3 +/- 3.6, P < .05). CNR was highest after Mangafodipir (-22.6 +/- 2.7), but this was not significantly different from others (P = .07). Overall, GRE images were superior to SE images for SNR and CNR. Mangafodipir and Gd-BOPTA (0.1 mmol/kg) provide equal liver enhancement and lesion conspicuity postcontrast. By all criteria, contrast-enhanced T1-weighted GRE were comparable to SE images.

Hepatic abscesses. Magnetic resonance imaging findings using gadolinium-BOPTA

RATIONALE AND OBJECTIVES

Gadolinium (Gd)-BOPTA was evaluated in a rabbit liver abscess model and compared with Gd-HP-DO3A, examining lesion conspicuity and characterization.

METHODS

Five New Zealand White rabbits with a liver abscess were studied on a 1.5-tesla Siemens Vision magnetic resonance unit. The disease model was created by surgically implanting a gel capsule filled with fusobacterium into the central or left lobe of the liver. For imaging, the animals were ventilated using a Harvard pump. Pancuronium bromide (0.12 mg/kg) was administered to allow acquisition of breath-hold scans. Magnetic resonance scans were obtained in each animal on days 2 and 3 after surgery. Every animal was studied twice, once after intravenous injection of 0.3 mmol/kg Gd-HP-DO3A (gadoteridol; ProHance) and once after intravenous injection of 0.1 mmol/kg Gd-BOPTA (gadobenate dimeglumine; MultiHance). The order of injection for the two agents was randomized with the two studies in each animal, separated by 24 hours to permit clearance. Image acquisition was performed in each instance with respiration suspended. Baseline two-dimensional spin-echo T1-weighted and fast spin-echo T2-weighted breath-hold scans were obtained first. The voxel dimensions were 5 x 0.8 x 0.8 mm3. Imaging times were 23 seconds for the T1-weighted scan and 26 seconds for the T2-weighted scan. Postcontrast scans, using spin-echo T1-weighted technique, were obtained at 1, 3, 5, and 15 minutes after contrast injection, whether Gd-HP-DO3A or Gd-BOPTA was used. Additional scans were obtained at 30, 45, and 60 minutes after Gd-BOPTA administration. At the completion of imaging on day 3, each animal was killed and the liver was removed and taken to a veterinary pathologist at the University's animal disease diagnostic lab for gross and histologic examination.

RESULTS

The enhancement of normal liver parenchyma, assessed by region of interest measurement and specifically as (SI(t) - SI0)/SI0 x 100, peaked at 119 +/- 37% 1 minute after injection of 0.3 mmol/kg Gd-HP-DO3A and at 126 +/- 30% 30 minutes after injection of 0.1 mmol/kg Gd-BOPTA. The difference in enhancement achieved, comparing results at each time point, was statistically significant only at 1 and 3 minutes postcontrast (P = 0.003 and 0.03). Lesion conspicuity, specifically (SIliver - SIlesion/noise), increased from 272 +/- 29 precontrast to a maximum of 639 +/- 73 at 30 minutes postcontrast using a dose of 0.1 mmol/kg Gd-BOPTA, with the improvement statistically significant (P = 0.0003). Lesion conspicuity on the T2-weighted scan was 137 +/- , with the Gd-BOPTA scan markedly superior (P = 0.00004). On scans at 45 and 60 minutes after Gd-BOPTA administration, a progressive increase in signal intensity in the central necrotic portion of the lesion was observed. This was most consistent with gradual diffusion of the agent from the adjacent liver into the lesion. Using Gd-HP-DO3A at 0.3 mmol/kg (three times the dose for Gd-BOPTA), lesion conspicuity increase from 305 +/- 37 precontrast to a maximum of 701 +/- 92 at 1 minute postcontrast, with this difference also statistically significant (P = 0.0004). The abscess rim exhibited moderate contrast enhancement, greater than that of normal liver parenchyma, on early postcontrast images with Gd-HP-DO3A.

CONCLUSIONS

The conspicuity of an early liver abscess is improved markedly on delayed imaging after administration of 0.1 mmol/kg Gd-BOPTA. Although a similar magnitude of parenchymal enhancement can be obtained after the administration of an extracellular agent, such as Gd-HP-DO3A, high-contrast dose (0.3 mmol/kg) and early dynamic imaging are required. The appearance of a liver abscess on late scans (45 to 60 minutes) after Gd-BOPTA injection is distinct from that of nonnecrotic metastases, with diffusion of the agent into the lesion noted.

Nuclear magnetic relaxation dispersion studies of water-soluble gadolinium(III)-texaphyrin complexes

Water proton 1/T1 nuclear magnetic relaxation dispersion (NMRD) profiles were measured for a water-soluble gadolinium(III) texaphyrin (Gd-tex) complex as a function of temperature and in the presence and absence of 5% human serum albumin (HSA). Upon dissolving the complex in water (0.259 mM), the water relaxivity values decreased with time but remained higher than those of free GD3+(aq) at all fields. Concurrent measurements of free Gd3+ using metallochromic dyes indicated that demetallation of the texaphyrin did not occur over a period of several days at 37 degrees C. The high relaxivity values and shape of the NMRD profile of this complex may be ascribed to a combination of large water coordination number (q estimated at 3.5) and long tau R. Upon mixing an aqueous solution of the complex with 5% HSA, the low-field water relaxivity slightly decreased whereas the high-field relaxivity increased relative to the free complex in water, and the relaxivities became nearly independent of temperature. These observations indicate that water exchange between the inner coordination sphere of Gd-tex and bulk water becomes limiting in the presence of HSA.

Magnetic resonance imaging with superparamagnetic iron oxide particles to evaluate hepatic macrophage-monocytic phagocytosis after arterial devascularization in minipigs

RATIONALE AND OBJECTIVES

We examined the effects of arterial ischemia on the phagocytic activity of the hepatic macrophage-monocytic phagocytic system (MMPS).

METHODS

Six minipigs were studied before and 24 hr after complete arterial devascularization of the liver. Magnetic resonance (MR) imaging was performed at 1.5 T using superparamagnetic iron oxide (SPIO) particles (18 mumol Fe/kg body weight) as an MMPS-specific contrast agent. Hepatobiliary scintigraphy, measurements of serum liver enzymes, and histology also were obtained.

RESULTS

On MR imaging, the postcontrast-to-precontrast ratios of the arterially devascularized livers were significantly higher than the corresponding baseline values (p < .01). The greatest difference (52%) between the baseline and the postoperative values was observed on gradient-echo (GE) images. Scintigraphy, laboratory analyses, and histology results indicate that the MR imaging findings were probably predominantly attributable to a reduction in phagocytic activity of the hepatic MMPS.

CONCLUSION

SPIO particles have already proved useful for improving detection of liver neoplasms on MR imaging, but they also may provide a novel way of evaluating the function of the hepatic MMPS in liver diseases.

Hepatic transport of the magnetic resonance imaging contrast agent gadobenate dimeglumine in the rat

RATIONALE AND OBJECTIVES

Gadobenate dimeglumine is a new octadentate gadolinium (III) complex salified with meglumine. The compound is currently under evaluation as an intravenously administered paramagnetic contrast agent for magnetic resonance (MR) imaging. We investigated the mechanisms involved in the biliary excretion of gadobenate ion, the contrast-effective ion in gadobenate dimeglumine.

METHODS

Biliary and urinary excretion of gadobenate ion injected intravenously to rats at 0.25 mmol/kg was studied following pretreatment with bromosulfophthalein (BSP) disodium salt, sodium taurocholate (TC), or oxyphenonium bromide (OP) and at various times after common bile duct ligation. Gadobenate ion was assayed by high-pressure liquid chromatography in bile and urine. Plasma bilirubin levels after duct ligation were measured by colorimetric assay.

RESULTS

The 90-min excretion of gadobenate ion into bile accounted for 35.5 +/- 3.7% and excretion into urine for 45.7 +/- 3.5% of the injected dose (mean +/- SD). Pretreatment with BSP reduced recovery of the compound in bile to less than 1% and increased urinary excretion to 65.6 +/- 4.7%. Gadobenate dimeglumine had a substantial choleretic effect that was completely abolished by pretreatment with BSP. Pretreatment with TC and OP did not change the biliary or urinary excretion of gadobenate ion. Surgical cholestasis led to a massive increase in plasma bilirubin levels from 3.9 +/- 2.2 (day of surgery) to 129 +/- 37 mumol/L (4 days after common bile duct ligature) and decreased 6-hr cumulative biliary excretion of gadobenate ion from 45 +/- 16% to 5.3 +/- 4.2% of the injected dose. Urinary excretion increased correspondingly from 49 +/- 15% to 83 +/- 12%.

CONCLUSION

The transport of gadobenate ion from plasma to bile occurs in the rat mainly through the BSP/bilirubin transport systems.

Preclinical evaluation of manganese carbonate particles for magnetic resonance imaging of the liver

RATIONALE AND OBJECTIVES

We characterized the physical, biological, and imaging properties of a manganese (Mn) carbonate particle suspension, a contrast agent for hepatic magnetic resonance (MR) imaging.

METHODS

Mn carbonate suspensions were produced by controlled precipitation and characterized using light microscopy, transmission electron microscopy, and in vitro relaxivity studies. Efficacy of the agent was studied in normal and tumor-bearing rats using T1-weighted MR imaging.

RESULTS

Following intravenous injection of Mn carbonate particles at doses ranging from 10 to 100 mumol Mn/kg, peak hepatic contrast enhancement of approximately 35% occurred from about 125 min until the termination of the MR imaging studies that varied from 125 to 305 min. Lesion conspicuity was increased because of relative intensity differences between normal liver and tumor. Data also showed that Mn carbonate particles dissolved on delivery to the liver, allowing Mn to interact with intrahepatic macromolecular complexes to provide positive contrast enhancement.

CONCLUSION

Mn carbonate particles produce significant and sustained hepatic enhancement and should improve detection of small or isointense liver lesions.

Preparation, physico-chemical characterization, and relaxometry studies of various gadolinium(III)-DTPA-bis(amide) derivatives as potential magnetic resonance contrast agents

Macroscopic protonation constants were measured for a series of DTPA mono- and bis-amide ligands using potentiometric titrations. Proton NMR pH titrations yielded protonation populations of the various nitrogen and oxygen basic sites of the ligands for the different protonation stages. Amide formation decreased the basicity of the backbone nitrogens of the ligands and the thermodynamic stability of the corresponding Gd3+ chelates. Nuclear magnetic relaxation dispersion (NMRD) profiles and ESR linewidths were measured for the Gd3+ chelates. Some of these exhibited an elevated high field relaxivity relative to Gd(DTPA)2-, in response to their high molecular weight. As opposed to Gd(DTPA)2-, at 5 degrees C the chemical exchange process of the single inner-sphere water molecule of the bis-amide complexes becomes so slow that it governs the paramagnetic relaxation process, causing the observed NMRD profiles to be close to those expected for the outer-sphere contribution. The chelates containing long alkyl side chains, such as Gd(DTPA-HPA2), showed increased relaxivity values in the presence of human serum albumin (HSA), indicative of noncovalent interaction with the protein. These chelates could be useful as nonionic hepatobiliary contrast agents.

Enhanced tumor detection in the presence of fatty liver disease: cell-specific contrast agents

It is assumed that hepatobiliary, cell-specific contrast agents will be adversely affected by the presence of diffuse liver disease. The diagnostic efficacy for tumor detection in the presence of fatty liver disease was experimentally studied at contrast-enhanced magnetic resonance (MR) imaging with manganese-DPDP (N,N'-dipyridoxylethylenediamine-N,N'-diacetate 5,5'-bis[phosphate]) and gadobenate dimeglumine (Gd-BOPTA/dimeg) and compared with conventional and chemical shift imaging. Carcinosarcoma was implanted into the liver of rats, and fatty liver was induced with L-ethionine. Without contrast agents, the tumor-fatty liver contrast-to-noise ratio (C/N) was increased on T1-weighted and decreased on T2-weighted MR images relative to tumor-bearing control rats without fatty liver. Chemical shift imaging (phase-contrast method) increased the tumor-fatty liver C/N from 2.3 +/- 1.0 to 6.1 +/- 1.7 (P < .001). Mn-DPDP and Gd-BOPTA/dimeg increased the tumor-fatty liver C/N from -5.4 +/- 1.6 to -11.0 +/- 1.9 and -9.8 +/- 3.4, respectively (P < .001). The hepatobiliary, cell-specific contrast agents were equally effective in both fatty and non-fatty liver and outperformed both chemical shift and conventional MR imaging in detecting liver tumors.

Evaluation of hepatocyte-specific paramagnetic contrast media for MR imaging of hepatitis

The hepatocyte-specific paramagnetic magnetic resonance (MR) contrast agents manganese-DPDP [N,N'-dipyridoxylethylenediamine-N,N'-diacetate 5,5'bis-(phosphate)] and gadobenate dimeglumine were used for diagnosing chemically induced hepatitis in rats. Ex vivo liver tissue relaxation times and in vivo MR image signal-to-noise ratios were compared before and after contrast agent administration. Ex vivo relaxometry and in vivo MR imaging showed that Mn-DPDP enhanced normal and diseased livers to the same degree at all time points from 5 to 120 minutes. Gadobenate dimeglumine showed reduced T1 and T2 enhancements in hepatitis relative to those of normal liver, in the early phase (5-30 minutes). However, these effects are offsetting, and as a result, MR imaging failed to allow distinction of diseased from normal livers. This surprising result observed in vivo was in fact predicted by applying the Bloch equation to our ex vivo data. Our results show that detection and quantitation of hepatitis with MR imaging enhanced with paramagnetic cell-specific contrast agents will be more difficult than anticipated.

Hepato-biliary and renal excretion in mice of charged and neutral gadolinium complexes of cyclic tetra-aza-phosphinic and carboxylic acids

Tissue distribution of 21 new 157/153Gd complexes was measured at 5 min and 24 hr after an intravenous injection into mice. A complex was judged to be stable in vivo when the percentage of 153Gd retained in the liver and skeleton at 24 hr was comparable with that of 153Gd(DOTA)-. Complexes varied in net charge and lipophilicity and 20 were phosphinic or carboxylic acid derivatives of tetra-aza-cyclo-dodecane. Three anionic, lipophilic complexes were cleared predominantly by the hepato-biliary pathway and were stable in vivo. The remaining 18 complexes were cleared mainly by the kidneys. Of these 18, 1 anionic, 8 neutral, and 3 cationic complexes were stable in vivo. These findings augur well for the future of hepato-biliary and general purpose Gd contrast enhancing agents for MRI.

Comparison of Gd-EOB-DTPA and Gd-DTPA for contrast-enhanced MR imaging of liver tumors

A new hepatobiliary contrast agent for magnetic resonance (MR) imaging, gadolinium-ethoxybenzyl (EOB)-diethylemetriaminepentaacetic acid (DTPA), was compared with Gd-DTPA to define the potential for improving tumor-liver contrast in a rodent liver adenocarcinoma model. With a T1-weighted spin-echo sequence, the contrast-to-noise ratio (C/N) for tumor before contrast agent administration was 5 (arbitrary units), the tumor appearing slightly hypo-intense with respect to liver parenchyma. After Gd-DTPA injection (0.1 mmol/kg), tumor enhanced more strongly than liver, resulting in an equalization of tumor and liver signal intensities and a decline in C/N to zero at 3 minutes after injection. After Gd-EOB-DTPA injection (0.1 mmol/kg), liver enhanced more strongly than tumor. Five minutes after injection, C/N increased from 5 to 25 and remained above 17 for 50 minutes. The data indicate that Gd-EOB-DTPA yields higher and more prolonged tumor-liver contrast than Gd-DTPA on T1-weighted spin-echo images. The high liver-tumor contrast after Gd-EOB-DTPA administration should prove clinically advantageous for MR imaging detection of focal hepatic masses.

Dual contrast enhancement of both T1- and T2-weighted sequences using ultrasmall superparamagnetic iron oxide

BMS 180549 (previously AMI-227), an ultrasmall superparamagnetic iron particulate agent, was investigated to determine its utility as a contrast agent on T1-weighted, as well as T2-weighted sequences, as a function of route of administration, (intravenous versus selective arterial) and concentration. Twelve farm pigs were divided into three groups of four each by route of administration (intravenous, selective superior mesenteric, or selective hepatic arterial injection). 10 mumol/kg and 20 mumol/kg dosages were given and evaluated both immediately after and 20-24 hr after contrast infusion, using both spin-echo and gradient-echo T1 and T2-weighted sequences. Significant postcontrast liver and spleen enhancement was noted at both concentrations, regardless of route of administration on both T1- and T2-weighted sequences. The earliest postcontrast T1-weighted sequence obtained during the 1-3 min interval following IV administration of high dose (20 mumol/kg) contrast demonstrated an average of +42.8% liver and +249.0% spleen enhancement; 24 hr later this decreased to 0 and 7.2%, respectively. The earliest postcontrast T2-weighted sequence obtained during the 8-17 min interval post high-dose IV contrast showed an average of -75.8% decrease in liver and -28.7% decrease in spleen signal intensity; 24 hr later the magnitude of these changes diminished to -33.1% and +2.5%, respectively. No significant difference was noted in liver or spleen enhancement, regardless of route of contrast administration (intravenous versus intraarterial).

Enhancement of tumor-liver contrast-to-noise ratio with gadobenate dimeglumine in MR imaging of rats

The efficacy for tumor detection of the hepatocyte-specific contrast agent gadobenate dimeglumine (gadolinium-BOPTA/Dimeg) was evaluated in four different experimental tumor models in rats. Histologic findings were correlated with quantitative data derived from ex vivo relaxometry and in vivo magnetic resonance (MR) imaging. Noninfiltrating tumors showed maximal enhancement of liver parenchyma 5-10 minutes after contrast agent administration, with a plateau over the next 30 minutes. In contrast, infiltrating tumors, which caused hepatocellular injury and inflammatory changes, delayed maximal enhancement of tumor-free parenchyma by 15-20 minutes. Nonspecific tumor enhancement depended on tumor vascularity and occurred in the early phase after contrast agent administration. Despite differences in specific enhancement of tumor-free parenchyma and nonspecific tumor enhancement, tumor-liver contrast-to-noise ratios increased 96%-248% in all tumor models 30 minutes after intravenous administration of 75 mmol/kg Gd-BOPTA/Dimeg. Gd-BOPTA/Dimeg enhanced tumor conspicuity independently of the histologic characteristics of the tumor.

Diagnosis of fatty liver with MR imaging

The diagnosis of fatty liver with magnetic resonance (MR) imaging was evaluated in experimental rat models of simple fatty infiltration and fatty liver with hepatocellular injury. T1 and T2 were measured ex vivo and correlated with the histologic degree of fatty infiltration. Enhancement of fatty liver with four different cells-specific contrast agents was studied with ex vivo relaxometry and in vivo MR imaging. Quantitative analysis of conventional and chemical shift MR images was correlated with biochemically determined fat content of the liver. Diet-induced simple fatty infiltration of the liver caused a decrease in T1 of 15%, whereas the T1 of L-ethionine-induced fatty liver with hepatocellular injury increased by 12%. T2 showed a positive correlation with the degree of fatty infiltration in both models. Cell-specific hepatobiliary contrast agents showed the same liver uptake and relaxation enhancement in fatty livers as in normal livers. Conventional T1-weighted images and chemical shift images showed good correlation (r = .83 and .80, respectively) between signal intensity and the degree of fatty infiltration. However, only chemical shift imaging was reliable in the diagnosis of fatty liver.

A new lipophilic gadolinium chelate as a tissue-specific contrast medium for MRI

Gd-Ethoxybenzyl-DTPA (Gd-EOB-DTPA) is a highly water-soluble paramagnetic contrast agent. Due to its protein binding of about 10% and its lipophilic residue, Gd-EOB-DTPA exhibits both renal (30% of the dose) and hepatobiliary (70%) excretion in rats. Despite its lipophilic character, the compound displays a low toxicity (LD50 = 7.5 mmol/kg). T1-relaxivity of 5.3 liters mmol-1 s-1 in water, 8.7 liters mmol-1 s-1 in plasma, and 16.9 liters mmol-1 s-1 in rat liver together with the hepatocellular uptake explain the liver-specific contrast enhancement of Gd-EOB-DTPA. The diagnostic dose is considerably lower than the amount of Magnevist used in abdominal imaging. The preclinical studies suggest its clinical role as being a hepatobiliary contrast agent for MRI.