Contrast-enhanced MR imaging of the liver

SYNTHESIS AND PROPERTIES OF Fe-MODIFIED CALCIUM-DEFICIENT HYDROXYAPATITE NANOCRYSTAL FOR MRI CONTRAST AGENT

In order to achieve for a better magnetic resonance imaging (MRI) contrast agent, the synthesis, degradation and magnetic properties of Fe -modified calcium deficient hydroxyapatite nanoparticles ( Fe -CDHAP, ( Ca , Fe )10-x( HPO 4)x( PO 4)6-x( OH )2-x), which synthesizes using ultrasonic assisted precipitation at low temperature, were investigated. The MRI contrast agent should be stable, biodegradable and also with great magnetism. The synthesized sample demonstrates needle-like morphology with dimension less than 50 nm in width and 300 nm in length under SEM. The structure and crystal deformation were studied by X-ray diffraction (XRD), which show 0.2% shrinkage in cell volume, through the pattern shifting and the lattice parameters calculations. Thermal gravity analysis (TGA) analysis indicated Fe -CDHAP were stable up to 1200°C and confirmed the structure of the Fe -CDHAP, which is stable. Fourier transform infrared spectroscopy (FTIR) assisted to define the influence of iron substitution and gave the hint of internal structure variation on [Formula: see text] sites that reflect on the great amount of phosphate ions release in acidic solution. The methods above prove the structure of Fe -CDHAP and also indicate the effect to [Formula: see text], which is caused by the doping of iron ions. The degradation test confirms the biodegradability of Fe -CDHAP that can degrade faster than CDHAP and also release a great amount of phosphate ions in a short time. The magnetic property of CDHAP and Fe -CDHAP were determined with VSM to and found the transformation of diamagnetic into paramagnetic.

Detection and characterization of liver lesions using gadoxetic acid as a tissue-specific contrast agent

The value of cross-sectional liver imaging is evaluated by the accuracy, sensitivity, and specificity of the specific imaging technique. Magnetic resonance imaging (MRI) has become a key technique for the characterization and detection of focal and diffuse liver disease. More recently, gadoxetic acid, the hepatocyte-specific MR contrast agent, was clinically approved and introduced in many countries. Gadoxetic acid may be considered a "molecular imaging" probe because the compound is actively taken into hepatocytes via the ATP-dependent organic anion transport system in the plasma membrane for the hepatic uptake. The transport of gadoxetic acid from the cytoplasm to the bile is mainly determined by the capacity of the transport protein glutathione-S-transferase. Gadoxetic acid enhances hepatocyte-containing lesions and improves detection of lesions devoid of normal hepatocytes, such as metastases. Innovative rapid MR acquisition techniques with near isotropic 3D pulse sequences with fat saturation parallel the technical progress made by multidetector computed tomography combined with an impressive improvement in tumor-liver contrast when used for gadoxetic acid-enhanced MRI. The purpose of this review is to provide an overview of the development, clinical testing, and applications of this novel MR contrast agent.

Detection of small hepatocellular carcinoma: comparison of conventional gadolinium-enhanced MRI with gadolinium-enhanced MRI after the administration of ferucarbotran

We compared the diagnostic efficacy of gadolinium (Gd)-enhanced MRI with that of Gd-enhanced MRI after administration of ferucarbotran for revealing small hypervascular hepatocellular carcinomas (HCCs). 24 patients with 34 HCCs (ranging in size from 0.6-2.0 cm) underwent Gd-enhanced three-dimensional dynamic MRI followed, after an interval of 5-11 days (mean, 7 days), by Gd-enhanced three-dimensional dynamic MRI after administration of ferucarbotran. The two Gd-enhanced arterial-phase MRI scans were compared quantitatively by measuring the tumour-liver contrast-to-noise ratio (CNR) and qualitatively by evaluating the tumour-liver contrast using matched-pairs analysis. The tumour-liver CNR with Gd-enhanced arterial-phase imaging after ferucarbotran (250.3 +/- 103.7) was higher than that with Gd-enhanced arterial-phase imaging (221.1 +/- 96.1) (p < 0.001). Matched-pairs analysis indicated that, for three lesions, the relative tumour-liver contrast was slightly better with Gd-enhanced arterial-phase imaging after ferucarbotran than with conventional Gd-enhanced arterial-phase imaging; however, in the case of the remaining 31 lesions, the two images were equivalent. We concluded that, although Gd-enhanced arterial-phase imaging after ferucarbotran results in better tumour-liver CNR than Gd-enhanced arterial-phase imaging, the ability of the two techniques to reveal small hypervascular HCCs is the same.

Double-dose 1.0-M gadobutrol versus standard-dose 0.5-M gadopentetate dimeglumine in revealing small hypervascular hepatocellular carcinomas

The purpose of this study was to compare the diagnostic efficacy of double-dose 1.0-M gadobutrol with that of standard-dose 0.5-M gadopentetate dimeglumine for revealing small hypervascular hepatocellular carcinomas (HCCs). Twenty-three patients with 37 HCCs (mean size: 1.2 cm) that were diagnosed by histology (n = 13) or imaging findings (n = 10) underwent two separate 3D dynamic MRIs with 0.2 mmol/kg of gadobutrol and 0.1 mmol/kg of gadopentetate dimeglumine. Three observers interpreted both MRIs in terms of lesion detection using the alternative-free response receiver operating characteristic method and lesion-to-liver contrast using matched pairs analysis. The two MRIs were also compared quantitatively by measuring the signal-to-noise ratio (SNR) of the liver and lesion as well as the lesion-liver contrast-to-noise ratio (CNR). The SNR of the liver and lesion and lesion-liver CNR with gadobutrol were better than those with gadopentetate dimeglumine (p < 0.01). However, in terms of the diagnostic accuracy (mean Az for gadobutrol: 0.878, and mean Az for gadopentate dimeglumine: 0.873), the sensitivity (92.8%), positive predictive value (92.8% vs. 93.7%) and lesion-liver contrast, the two dynamic MRIs were equivalent. Gadobutrol showed a superior degree of enhancement for hypervascular HCC than did gadopentetate dimeglumine, but the diagnostic capabilities of the two agents for revealing HCCs were equivalent.

Superparamagnetic iron oxide-enhanced liver magnetic resonance imaging: comparison of 1.5 T and 3.0 T imaging for detection of focal malignant liver lesions

OBJECTIVES

We sought to compare the image quality, lesion conspicuity, and the diagnostic performance of 1.5 T and 3.0 T superparamagnetic iron oxide-enhanced liver magnetic resonance imaging (MRI) for detecting focal malignant hepatic lesions.

MATERIALS AND METHODS

A total of 35 patients with pathologically proven liver malignancy underwent both 1.5 and 3.0 T SPIO-enhanced MRI. The diagnostic accuracy was evaluated using the alternative-free response receiver operating characteristic method. Image artifacts, quality, and the lesion conspicuity were analyzed. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the lesion were calculated.

RESULTS

No significant difference of area under ROC curve (Az value) was noted. The mean SNR and CNR of the lesions was higher in the 3.0 T sets. There was no difference between the 1.5 T and the 3.0 T image sets for lesion conspicuity, but the image quality was better on 1.5 T. Motion and susceptibility artifacts were more frequent on 3.0 T.

CONCLUSION

Diagnostic accuracies of the SPIO-enhanced MRI were equivalent on the 1.5 T and 3.0 T image sets. More prominent artifacts on 3.0 T superparamagnetic iron oxide-enhanced liver MRI counteracted advantage of higher SNR and CNR of 3.0 T.

Efficacy and safety of mangafodipir trisodium (MnDPDP) injection for hepatic MRI in adults: results of the U.S. Multicenter phase III clinical trials. Efficacy of early imaging

The efficacy of contrast-enhanced magnetic resonance imaging (MRI) for detecting and characterizing, or excluding, hepatic masses was assessed in 404 patients, following the intravenous administration of mangafodipir trisodium (MnDPDP) injection, a hepatic MRI contrast agent. An initial contrast-enhanced computed tomography (CT) examination was followed by unenhanced MRI, injection of MnDPDP (5 micromol/kg IV), and enhanced MRI at 15 minutes post injection. Agreement of the radiologic diagnoses with the patients' final diagnoses was higher for enhanced MRI and for the combined unenhanced and enhanced MRI evaluations than for unenhanced MRI alone or enhanced CT using the clinical diagnosis as the gold standard. Mangafodipir-enhanced MRI uniquely provided additional diagnostic information in 48% of the patients, and patient management was consequently altered in 6% of the patients. MnDPDP-enhanced MRI was comparable or superior to unenhanced MRI and enhanced CT for the detection, classification, and diagnosis of focal liver lesions in patients with known or suspected focal liver disease.

Contrast media in liver sonography: correlation with enhanced dynamic magnetic resonance imaging

Both color Doppler sonography and magnetic resonance are imaging techniques which do not use ionizing radiations, but despite this common feature there remain many differences between them. Thus, color Doppler sonography is a cost-effective technique using mechanical waves and providing real-time images while magnetic resonance imaging is much more expensive, uses magnetic fields and radiofrequency energy and provides static images. The former method is very sensitive in detecting focal liver lesions > 1 cm, but its specificity in characterization is not as good, not even with the color Doppler technique. The main differences between color Doppler sonography, with and/or without echocontrast agents, and contrast-enhanced (Gadolinium chelates) dynamic magnetic resonance imaging in focal liver lesions can be summarized as follows: (1) magnetic resonance imaging depicts tumor vascularization only after paramagnetic contrast media injection. Enhanced images completely depend upon the contrast agent and cannot be achieved without it. In contrast, color Doppler signal is not modified by the contrast agent, it just becomes stronger. (2) Contrast-enhanced magnetic resonance signal (as well as contrast-enhanced computed tomography signal) provides more pieces of information than color Doppler signal about the flow characteristics of liver nodules--i.e. it shows not only blood flow (hyper-/hypovascular nodule), but also the interstitial spread of the agent and its wash-out. For example, hepatocellular carcinoma and focal nodular hyperplasia have similar perfusion while agent spread and wash-out decrease very quickly in the former and more slowly in the latter, except for the low decrease of the central scar. (3) Color Doppler technology improvements, higher sensitivity to slow flows and better signal/noise ratio reduce the applications of contrast-enhanced sonography in focal liver lesions because the agents modify only sensitivity and not the imaging in slow flow studies. (4) The higher cost of contrast studies is justified only in selected cases, namely treatment follow-up in the lesions with rich pretreatment vascularization. Finally, the higher cost of contrast magnetic resonance studies is justified to increase sensitivity and especially to allow lesion characterization.

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.

Early dynamic magnetic resonance imaging of liver metastases with 0.3 and 0.6 mmol/kg gadoteridol injection

RATIONALE AND OBJECTIVES

The potential for improvement in liver-lesion conspicuity on early dynamic scans after bolus intravenous gadolinium (Gd) chelate administration was evaluated using gadoteridol (Gd-HP-DO3A; Prohance) at doses of 0.3 and 0.6 mmol/kg.

METHODS

Five New Zealand white rabbits with focal VX-2 adenocarcinoma liver metastases were studied on a 1.5-tesla Siemens Vision scanner. Each rabbit was imaged twice (on two separate days), after injections of 0.3 mmol/kg and 0.6 mmol/ kg Gd-HP-DO3A. The contrast dose (0.3 or 0.6 mmol/kg) was given as a single intravenous injection. The order of injection for the two doses was randomized, with the two studies (in any one rabbit) separated by 24 hours to allow for clearance. Contrast was administered using an autoinjector at a rate of 1.5 mL/second. Turbo-fast low-angle shot scans were obtained before and at 6, 12, 19, 25, 31, 60, 120, 180, 240, 300, and 600 seconds after contrast injection. The lesions were confirmed, after killing the rabbit, by gross and microscopic examination.

RESULTS

The enhancement of normal liver parenchyma, assessed by (SIt-SIo)/SIo.100, (SI = signal intensity) peaked at 32% +/- 4% 19 seconds after injection of 0.3 mmol/kg and at 38% +/- 5% 31 seconds after injection of 0.6 mmol/kg. The difference in maximum parenchymal enhancement achieved, comparing the 0.3 and 0.6 mmol/kg doses, was statistically significant (P < 0.03). Lesion conspicuity, specifically (SIliver-SIlesion/noise), increased from 4.5 +/- 2.3 precontrast to a maximum of 6.8 +/- 1.2 at 19 seconds postcontrast using a dose of 0.3 mmol/kg, with the difference statistically significant (P < 0.03). The increase with a dose of 0.6 mmol/kg was from 4.2 +/- 0.7 to 6.5 +/- 1.9 with this difference also statistically significant (P < 0.02). There was no statistically significant difference in lesion conspicuity between the doses of 0.3 and 0.6 mmol/kg.

CONCLUSIONS

Conspicuity of liver metastases can be improved substantially with dynamic magnetic resonance imaging and rapid intravenous bolus contrast injection with a dose of 0.3 mmol/kg. No further improvement is noted at a dose of 0.6 mmol/kg, despite greater positive contrast enhancement of normal liver parenchyma.

Comparison of gadolinium chelates with manganese-DPDP for liver lesion detection and characterization: preliminary results

Nonspecific extracellular gadolinium chelate (NEGd) was prospectively compared with managanese (Mn)-DPDP (Mn) for the detection and characterization of focal liver lesions of various histology. Seventeen patients with known or suspected focal liver lesions underwent NEGd and Mn-enhanced studies at 1.5 T. Study findings were correlated with histology (five patients), computed tomography (CT) examinations (17 patients), and 4- to 13-month imaging follow-up by CT and/or MR (five patients). NEGd studies were performed as serial postcontrast spoiled gradient echo (SGE) sequences, and Mn studies were performed as SGE sequences 15 and 30 min postocontrast and T1-weighted, fat-suppressed spin echo at 16 min. NEGd and Mn images were prospectively interpreted in a separate blinded fashion. Lesion detection and characterization were determined. NEGd and Mn-enhanced images demonstrated 61 and 49 lesions, respectively (p = .1, NS). A total of 60 and 33 lesions were characterized on NEGd and Mn images, respectively, which was significantly different (p = .008). No differences were observed for the detection and characterization of liver metastases; whereas there was a trend for superior detection and characterization for hepatocellular carcinoma with NEGA.

Evaluation of gadolinium 2,5-BPA-DO3A, a new macrocyclic hepatobiliary chelate, in normal liver and metastatic disease on high field magnetic resonance imaging

RATIONALE AND OBJECTIVES

A new hepatobiliary gadolinium chelate, gadolinium (Gd) 2,5-BPA-DO3A, was compared in two animal species with Gd HP-DO3A (gadoteridol), a clinically approved extracellular contrast agent, and Gd Cy2-DOTA, a second hepatobiliary chelate in preclinical development. The ligand in Gd 2,5-BPA-DO3A is macrocyclic in nature, as opposed to the linear structure of Gd DTPA. Gadolinium 2,5-BPA-DO3A was evaluated on magnetic resonance imaging at 1.5 T, examining specifically liver parenchymal enhancement and lesion delineation, the latter in metastatic disease.

METHODS

Gadolinium 2,5-BPA-DO3A was evaluated in five normal rhesus monkeys and four New Zealand White rabbits with implanted VX-2 liver tumors. These studies were compared with magnetic resonance exams in the same animals using Gd HP-DO3A and Gd Cy2-DOTA. A contrast dose of 0.1 mmol/kg intravenous was employed in each instance, with the sequence of administration (for the three agents) randomized and at least 72 hours between injections. Spin echo breathhold T1-weighted scans were obtained before and at multiple times after contrast administration. Postcontrast scans were acquired from 1 to 60 minutes after injection in the monkeys and from 1 to 240 minutes in the rabbits.

RESULTS

Enhancement of normal liver parenchyma was markedly superior with Gd 2,5-BPA-DO3A compared with Gd HP-DO3A and Gd Cy2-DOTA in both monkeys and rabbits. At 2 and 60 minutes after contrast administration, the liver signal intensity in the monkey was 452 +/- 56 and 440 +/- 69 with Gd 2,5-BPA-DO3A compared with 295 +/- 34 and 256 +/- 38 with Gd HP-DO3A. The difference between agents was statistically significant at all postcontrast time points in the rhesus monkey. Excretion of contrast into the gall bladder was consistently observed after Gd 2,5-BPA-DO3A injection in both animal species. Maximum lesion conspicuity occurred in the rabbit at 45 minutes after Gd 2,5-BPA-DO3A administration. At 45 minutes postinjection, liver-lesion contrast was 0.60 +/- 0.15 with Gd 2,5-BPA-DO3A, 0.35 +/- 0.11 with Gd Cy2-DOTA, and 0.12 +/- 0.04 with Gd HP-DO3A, with the differences between agents being statistically significant.

CONCLUSIONS

Gadolinium 2,5-BPA-DO3A is superior to both Gd Cy2-DOTA and Gd HP-DO3A in the degree of enhancement of normal liver parenchyma achieved after intravenous injection. This leads to improved liver lesion delineation with Gd 2,5-BPA-DO3A on delayed postcontrast magnetic resonance scans.

Surface properties of superparamagnetic iron oxide MR contrast agents: ferumoxides, ferumoxtran, ferumoxsil

The surface properties of the active ingredients in AMI colloidal, superparamagnetic iron oxide magnetic resonance (MR) contrast agents are described. Scanning electron microscopy/energy dispersive X-ray elemental analyses and diffuse reflectance Fourier transform infrared spectroscopy (FTIR) spectra of ferumoxsil (AMI-121 drug substance) were consistent with the presence of a monolayer of H2NCH2CH2NHCH2CH2CH2Si(O-)3 siloxane monomer or dimer. The X-ray photoelectron spectra (XPS) of ferumoxsil are also consistent with complete coverage of the iron oxide surface with a monolayer of siloxane. The static secondary ion mass spectra (SSIMS) of ferumoxsil showed that the siloxane film is covalently bonded (i.e., Si-O-Fe bonds) to the iron oxide surface. The FTIR of ferumoxides (AMI-25) and Ferumoxtran (AMI-227) showed only adsorbed dextran. The XPS spectra of the dextran-coated colloids showed that Ferumoxtran has a thicker layer of dextran than ferumoxides iron oxide particles (approximately 5 and approximately 3 nm, respectively). The SSIMS spectra of these dextran-coated colloids showed only low mass fragments due to the adsorbed dextran. The nature of the interactions of the dextran coating with the iron oxide surfaces of ferumoxides and Ferumoxtran is discussed.

Physical and chemical properties of superparamagnetic iron oxide MR contrast agents: ferumoxides, ferumoxtran, ferumoxsil

The bulk physiochemical properties of the active ingredients in three AMI colloidal, superparamagnetic iron oxide (SPIO), MR contrast agents are described. Ferrous content and X-Ray diffraction (XRD) of the colloids are consistent with nonstoichiometric magnetite phases in all three active ingredients. No separate maghemite (gamma-Fe2O3) phases were detected by XRD. XRD line-broadening determinations of representative samples of ferumoxides (dextran coated), Ferumoxtran (dextran covered), and ferumoxsil (siloxane coated) yielded mean crystal diameters (volume weighted distribution) of 4.8-5.6, 5.8-6.2, and 7.9-8.8 nm, respectively. Transmission electron microscopy (TEM) showed that the crystal sizes were lognormally distributed with respective mean crystal diameters (number weighted distribution) of 4.3-4.8, 4.3-4.9, and 8.0-9.5 nm, respectively. Consistent with their small crystal sizes, the three SPIO colloids are superparamagnetic with no remanence after saturation at high applied fields (< 1 T), and showed characteristic relaxed Mössbauer spectra. The Mössbauer spectra of ferumoxides and Ferumoxtran were consistent with the presence of superparamagnetic relaxation above a blocking temperature of approximately 60 K. Due to the larger crystal sizes of ferumoxsil, its Mössbauer spectra showed the presence of rapid collective magnetic excitations on the Mössbauer time scale (approximately 1-10 ns). All three colloids showed high MR relaxivities. TEM of the SPIO colloids showed that ferumoxides and ferumoxsil are composed of aggregates of nonstoichiometric magnetite crystals, while Ferumoxtran consists of single crystals of nonstoichiometric magnetite. Dynamic light scattering (PCS) measurements showed that Ferumoxtran particles have average hydrodynamic diameters of approximately 21 nm (number weighted distribution) or 30 nm (volume weighted distribution). The data indicate that Ferumoxtran crystals are coated with an 8-12 nm layer of dextran T-10. Ferumoxides aggregates have average particle sizes of approximately 35 nm (number average distribution; TEM and PCS), or approximately 50 nm (volume weighted distribution; PCS). Mean sizes of ferumoxsil aggregates are approximately 300 nm (intensity weighted distribution). A discussion of the various particle size distributions is presented.