MR contrast agents: Physical and pharmacologic basics

Properties evaluation of a new MRI contrast agent based on Gd-loaded nanoparticles

Nanosized materials of gadolinium oxide can provide high-contrast enhancement in magnetic resonance imaging (MRI). The aim of this research was to characterize a novel emulsion composed of a silicon-based nanocomposite polymer (NCP) and gadolinium (III) oxide (Gd₂O₃) nanoparticles. The size and morphological structure of this nanoparticle are determined by particle size analysis device (zeta sizer) and transmission electronic microscope. We determined composition of Gd₂O₃ nanoparticles with energy dispersive X-ray analysis (EDXA) and magnetic resonance signal by T₁-weighted MRI. Cytotoxicity of Gd₂O₃ nanoparticles in SK-MEL-3 cancer cells was evaluated. Zeta sizer showed Gd₂O₃ nanoparticles to be 75 nm in size. EDXA indicated the two main chemical components of gadolinium-nanocomposite polymer emulsion: gadolinium and silicon and MRI also showed a significantly higher incremental relaxivity for Gd₂O₃ nanoparticles compared to Magnevist (conventional contrast agent). In such concentrations, the slope of R₁ relaxivity (1/T₁) vs. concentration curve of Magnevist and Gd₂O₃ were 4.33, 7.98 s⁻¹ mM⁻¹. The slope of R₂ relaxivity (1/T₂) vs. concentration curve of Magnevist and Gd₂O₃ were 5.06, 13.75 s⁻¹ mM⁻¹. No appreciable toxicity was observed with Gd₂O₃ nanoparticles. Gadolinium-nanocomposite polymer emulsion is well characterized and has potential as a useful contrast agent for magnetic resonance molecular imaging.

The effect of gadoxetic acid enhancement on lesion detection and characterisation using T₂ weighted imaging and diffusion weighted imaging of the liver

OBJECTIVES

To evaluate the effect of gadoxetic acid enhancement on the detection and characterisation of focal hepatic lesions on T(2) weighted and diffusion weighted (DW) images.

METHODS

A total of 63 consecutive patients underwent T(2) weighted and DW imaging before and after gadoxetic acid enhancement. Two blinded readers independently identified all of the focal lesions using a five-point confidence scale and characterised each lesion using a three-point scale: 1, non-solid; 2, indeterminate; and 3, solid. For both T(2) weighted and DW imaging, the accuracies for detecting focal lesions were compared using the free-response receiver operating characteristic analysis; the accuracies for lesion characterisation were compared using the McNemar test between non-enhanced and gadoxetic acid-enhanced image sets. For hepatic lesions ≥ 1 cm, the lesion-to-liver contrast-to-noise ratio (CNR) and the apparent diffusion coefficient (ADC) were compared in the non-enhanced and enhanced image sets using the generalised estimating equations.

RESULTS

For both T(2) weighted and DW images, the accuracies for detecting focal lesions (p ≥ 0.52) and those for lesion characterisation (p ≥ 0.63) did not differ significantly between the non-enhanced and enhanced image sets. The lesion-to-liver CNR was significantly higher on enhanced DW images than on non-enhanced DW images (p=0.02), although the difference was not significant for T(2) weighted imaging (p=0.65). The mean ADC values of lesions did not differ significantly on enhanced and non-enhanced DW imaging (p=0.75).

CONCLUSION

The acquisition of T(2) weighted and DW images after administration of gadoxetic acid has no significant effect on the detection or characterisation of focal hepatic lesions, although it improves the lesion-to-liver CNR on DW images.

Responses of human skin in organ culture and human skin fibroblasts to a gadolinium-based MRI contrast agent: comparison of skin from patients with end-stage renal disease and skin from healthy subjects

OBJECTIVE

Nephrogenic systemic fibrosis is a clinical syndrome occurring in a small subset of patients with end-stage renal disease (ESRD). Exposure to certain of the gadolinium-based contrast agents during magnetic resonance imaging appears to be a trigger. The pathogenesis of the disease is largely unknown. The present study addresses potential pathophysiologic mechanisms.

MATERIALS AND METHODS

We have compared responses in organ-cultured skin and skin fibroblasts from individuals with ESRD to responses of healthy control subjects to Omniscan treatment.

RESULTS

Treatment of skin from ESRD patients with Omniscan stimulated production of matrix metalloproteinase-1 and tissue inhibitor of metalloproteinases-1, but not type I procollagen. The same treatment also stimulated an increase in hyaluronan production. Similar results were seen with skin from normal controls but basal levels were higher in ESRD patients. Fibroblasts in monolayer culture gave the same responses, but there were no differences based on whether the cells were isolated from the skin of healthy subjects or those with ESRD.

CONCLUSION

These data indicate that Omniscan exposure alters an enzyme/inhibitor system responsible for regulating collagen turnover in the skin and directly stimulates hyaluronan production. The higher basal levels of type I procollagen, matrix metalloproteinase-1, tissue inhibitor of metalloproteinases-1, and hyaluronan in the skin from ESRD patients could contribute to the sensitivity of this patient population to fibrotic changes, which might be induced by exposure to some of the gadolinium-based contrast agents.

In vivo molecular imaging using nanomaterials: general in vivo characteristics of nano-sized reagents and applications for cancer diagnosis

Nanoparticles present a new collection of contrast agents for the field of in vivo molecular imaging. This review focuses on promising molecular imaging probes for optical and magnetic resonance imaging based on four representative nanomaterial(s) platforms: quantum dots, upconversion phosphors, superparamagnetic iron oxides, and dendrimer-based agents. Quantum dots are extremely efficient fluorescent nanoparticles with size-tunable emission properties, enabling high sensitivity and greater depth penetration. Their heavy metal composition and long retention in the body, however, pose concerns for clinical translational applications. Upconversion phosphors generate excellent signal-to-background contrast because they emit light with higher energy than the excitation photons and autofluorescence signals. For MRI, iron oxide particles also generate excellent signal and have been used in liver imaging and for cell tracking studies. As they are metabolized through endogenous iron salvage pathways, they have already been introduced as clinical contrast agents. Lastly, dendrimers, a 'soft' nanoparticle, can be used as a structural basis for the attachment of small molecule imaging agents and/or targeting groups. This array of nanoparticles should offer insights into the uses and potentials of nanoparticles for the molecular imaging.

Effect of different classes of gadolinium-based contrast agents on control and nephrogenic systemic fibrosis-derived fibroblast proliferation

PURPOSE

To determine the ability of different types of gadolinium-based contrast agents (GBCAs) to stimulate fibroblast proliferation in monolayer cell culture.

MATERIALS AND METHODS

The National Health Service West Glasgow Ethics Committee granted approval for this study. Fibroblasts established from healthy volunteers (control subjects) and from lesional skin of patients with nephrogenic systemic fibrosis were exposed to a range of concentrations of ionic and nonionic linear and macrocyclic contrast agents over 4 days, and the effect on growth was determined. The lowest concentration of contrast agent that stimulated the maximum effect on fibroblast growth was selected for determination of its effect on fibroblast growth over 8 days. The effect of contrast agents on hyaluronan and collagen synthesis was determined with an enzyme-linked immunosorbent assay. Responses were assessed with analysis of variance (general linear model).

RESULTS

The linear gadolinium contrast agents (gadodiamide, gadoversetamide, gadopentetate dimeglumine, and gadobenate dimeglumine) produced a maximum stimulation of fibroblast proliferation at a concentration of 0.1 mmol/L, with cell numbers increasing up to 2.3-fold. The macrocyclic contrast agents (gadoteric acid and gadoteridol) produced a maximum stimulation of fibroblast proliferation at a concentration of 5 mmol/L. The reference gadolinium agents (N-methylglucamine gadolinium ethylenediaminetetraacetic acid and gadolinium trichloride) stimulated fibroblast proliferation at a concentration of 0.01 mmol/L and were toxic at a concentration greater than 1 mmol/L. Growth curves supported the dose-response observations. Hyaluronan synthesis was stimulated by gadoversetamide, gadobenate dimeglumine, gadodiamide, and gadopentetate dimeglumine at a concentration of 0.1 mmol/L and by gadolinium trichloride at a concentration of 0.01 mmol/L, whereas collagen synthesis was unaffected.

CONCLUSION

This study provides evidence that different classes of gadolinium chelates stimulate human fibroblast proliferation.

Evaluation of gadobutrol, a macrocyclic, nonionic gadolinium chelate in a brain glioma model: comparison with gadoterate meglumine and gadopentetate dimeglumine at 1.5 T, combined with an assessment of field strength dependence, specifically 1.5 versus 3 T

PURPOSE

To evaluate in a rat brain glioma model intraindividual tumor enhancement at 1.5 T using gadobutrol (Gadovist), a nonionic, macrocyclic chelate currently in clinical trials in the United States, in comparison with both an ionic macrocyclic chelate, gadoterate meglumine (Dotarem), and an ionic linear chelate, gadopentetate dimeglumine (Magnevist), and to compare the degree of tumor enhancement with gadobutrol at 1.5 and 3 T.

MATERIALS AND METHODS

A total of 24 rats, divided into three groups with n = 8 animals per group, were evaluated. Animals in group 1 received injections of gadobutrol and gadopentetate dimeglumine, whereas those in group 2 received gadobutrol and gadoterate meglumine. Injections were performed in random order and separated by 24 hours. Magnetic resonance imaging (MRI) examinations were performed immediately following each contrast injection with a 1.5 T MR system. Animals in group 3 received gadobutrol injections using the same protocol but with scans performed at 1.5 and 3 T. In all examinations, T1-weighted images were acquired precontrast, 1 minute postcontrast, and at 4 consecutive 2-minute intervals thereafter. A contrast dose of 0.1 mmol/kg was used in all instances.

RESULTS

In groups 1 and 2, tumor signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were higher for gadobutrol compared to both other agents at each timepoint postcontrast injection. The improvement in tumor CNR with gadobutrol, depending on time, was between 12% and 40% versus gadopentetate dimeglumine, with the difference achieving statistical significance at 7 minutes. The improvement in tumor CNR with gadobutrol, depending on time, was between 15% and 27% versus gadoterate meglumine, with the difference statistically significant at 5 and 9 minutes. In group 3 the improvement in tumor SNR and CNR seen with the increase in field strength from 1.5 to 3 T for gadobutrol was statistically significant at all acquired timepoints (P < 0.002). CNR mean values ranged from 10.4 +/- 2.9 to 24.6 +/- 5.0 at 1.5 T and from 20.5 +/- 5.9 to 47.8 +/- 15.7 at 3 T depending on the timepoint postcontrast.

CONCLUSION

Consistently greater tumor enhancement was noted at all measured timepoints following contrast injection with gadobutrol compared to both gadopentetate dimeglumine and gadoterate meglumine at 1.5 T. A substantial further improvement in tumor enhancement was noted using gadobutrol at 3 T.

Development of a signal-inducing bone cement for magnetic resonance imaging

PURPOSE

To develop a signal-inducing bone cement for musculoskeletal procedures in magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Acrylic resins were mixed with contrast agents (CAs) and water. We determined the ideal concentration of the components and assessed feasibility in cadaveric bones in an open high-field MR scanner. The contrast-to-noise ratio (CNR) in air and bone was evaluated and mechanical tests were achieved. We determined the amount of water that was not incorporated and measured the amount of CA released with photometric analysis. The cement was analyzed microscopically.

RESULTS

Preparation and application of the CA-water-cement compound was feasible and its differentiation in MRI was clear. The maximal CNR(air) had a value of 157.5 (SD 18.3) in an interventional fast T1W turbo-spin echo (TSE) sequence. The compressive strength decreased with the amount of water added. Although nearly 50% of the water added was not incorporated in the cement, the CNR was sufficient for cement detection. The threshold for systemic toxicity of delivered CA was not reached and the microscopic analysis showed water bubbles in the cement.

CONCLUSION

A signal-inducing bone cement is feasible for the use in MRI.

Collagenolytic activity is suppressed in organ-cultured human skin exposed to a gadolinium-based MRI contrast agent

OBJECTIVE

Human skin produces increased amounts of matrix metalloproteinase-1 (MMP-1) when exposed in organ culture to Omniscan, one of the gadolinium-based MRI contrast agents (GBCA). MMP-1, by virtue of its ability to degrade structural collagen, contributes to collagen turnover in the skin. The objective of the present study was to determine whether collagenolytic activity was concomitantly up-regulated with increased enzyme.

MATERIALS AND METHODS

Skin biopsies from normal volunteers were exposed in organ culture to Omniscan. Organ culture fluids obtained from control and treated skin were examined for ability to degrade type I collagen. The same culture fluids were examined for levels of MMP-1, tissue inhibitor of metalloproteinases-1 (TIMP-1), and complexes of MMP-1 and TIMP-1.

RESULTS

Although MMP-1 was increased in culture fluid from Omniscan-treated skin, there was no increase in collagenolytic activity. In fact, collagenolytic activity declined. Increased production of TIMP-1 was also observed in Omniscan-treated skin, and the absolute amount of TIMP-1 was greater than the amount of MMP-1. Virtually all of the MMP-1 was present in MMP-1-TIMP-1 complexes, but the majority of TIMP-1 was not associated with MMP-1. When human dermal fibroblasts were exposed to TIMP-1 (up to 250 ng/mL), no increase in proliferation was observed, but an increase in collagen deposition into the cell layer was seen.

CONCLUSION

Gadolinium-based MRI contrast agent exposure has recently been linked to a fibrotic skin condition in patients with impaired kidney function. The mechanism is unknown. The increase in TIMP-1 production and concomitant reduction in collagenolytic activity demonstrated here could result in decreased collagen turnover and increased deposition of collagen in lesional skin.

Breast cancer detection using automated whole breast ultrasound and mammography in radiographically dense breasts

PURPOSE

Mammography, the standard method of breast cancer screening, misses many cancers, especially in dense-breasted women. We compared the performance and diagnostic yield of mammography alone versus an automated whole breast ultrasound (AWBU) plus mammography in women with dense breasts and/or at elevated risk of breast cancer.

METHODS

AWBU screening was tested in 4,419 women having routine mammography (

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00649337). Cancers occurring during the study and subsequent 1-year follow-up were evaluated. Sensitivity, specificity and positive predictive value (PPV) of biopsy recommendation for mammography alone, AWBU and mammography with AWBU were calculated.

RESULTS

Breast cancer detection doubled from 23 to 46 in 6,425 studies using AWBU with mammography, resulting in an increase in diagnostic yield from 3.6 per 1,000 with mammography alone to 7.2 per 1,000 by adding AWBU. PPV for biopsy based on mammography findings was 39.0% and for AWBU 38.4%. The number of detected invasive cancers 10 mm or less in size tripled from 7 to 21 when AWBU findings were added to mammography.

CONCLUSION

AWBU resulted in significant cancer detection improvement compared with mammography alone. Additional detection and the smaller size of invasive cancers may justify this technology's expense for women with dense breasts and/or at high risk for breast cancer.

Detection of lymph node metastases by gadolinium-enhanced magnetic resonance imaging: systematic review and meta-analysis

BACKGROUND

Gadolinium-based contrast agents are used with magnetic resonance imaging (MRI) to highlight tumor vascularity in organs. They are also widely used for primary tumor visualization. We conducted a systematic review and meta-analysis of the existing evidence of the accuracy of gadolinium-enhanced MRI for staging lymph node metastases.

METHODS

We systematically searched the MEDLINE, Cochrane, CANCERLIT, and EMBASE databases for studies published in English or German from January 1, 1988, to January 1, 2008, that assessed the diagnostic accuracy of gadolinium-enhanced MRI in the evaluation of lymphatic metastases compared with histopathologic examination as the reference test. Based on a priori-defined clinical considerations, we studied three subgroups of studies: those that used a single malignancy criterion and those that used multiple malignancy criteria with or without contrast highlighting. Summaries of MRI sensitivity and specificity for detecting lymph node metastases were calculated using a bivariate regression model. All statistical tests were two-sided.

RESULTS

The literature search yielded 43 full-text papers that were considered for inclusion in the meta-analysis. We performed quantitative pooled analyses on the 32 studies that provided data on patient-level diagnosis. The weighted estimates of sensitivity and specificity for all studies combined were 0.72 (95% confidence interval [CI] = 0.66 to 0.79) and 0.87 (95% CI = 0.82 to 0.91). Estimates of sensitivity and specificity were essentially unchanged for studies that used a single malignancy criterion (0.71 [95% CI = 0.61 to 0.79] and 0.88 [95% CI = 0.80 to 0.93], respectively; n = 11 studies) or multiple malignancy criteria without contrast enhancement (0.70 [95% CI = 0.58 to 0.79] and 0.86 [95% CI = 0.68 to 0.94], respectively; n = 6 studies). The sensitivity increased to 0.84 (95% CI = 0.70 to 0.92), with a specificity of 0.82 (95% CI = 0.72 to 0.89) for the nine studies that incorporated contrast enhancement in their multiple malignancy criteria. Six studies did not define the malignancy criteria they used.

CONCLUSIONS

The overall accuracy of gadolinium-enhanced magnetic resonance imaging for the detection of nodal metastases is moderate. Incorporating contrast enhancement in the malignancy criteria substantially improves the accuracy of this diagnostic test.

Accelerated blood clearance was not induced for a gadolinium-containing PEG-poly(L-lysine)-based polymeric micelle in mice

PURPOSE

Accelerated blood clearance (ABC) is induced by repeated injections of PEGylated liposomes. In this study, the ABC was investigated for a gadolinium-containing PEG-poly(L-lysine)-based polymeric micelle (Gd-micelle) and PEGylated liposome (Gd-liposome) in mice.

MATERIALS AND METHODS

Effects of the first injection of Gd-micelle on the tissue distribution of the second dose of Gd-micelle were studied. Additionally, effects of the first injection of Gd-micelle, Gd-liposome, empty liposome, polyethyleneglycol (PEG(500,000)), and PEG-lipid on the distribution of the second dose of the Gd-liposome were evaluated.

RESULTS

Results indicated that the tissue distribution of the second injection of the Gd-micelle at a dose of 33, 5, or 2 micromol Gd/kg was not affected by the first injection of the Gd-micelle at different doses and time intervals or of the empty PEGylated liposome 7 days before. ABC of Gd-liposome at a dose of 2.3 micromol Gd/kg (corresponding to 10 micromol lipids/kg) was observed when the empty PEGylated liposome or Gd-liposome, but not the Gd-micelle, PEG(500,000) or PEG-lipid, was pre-administered.

CONCLUSIONS

The hydrophobic core of the micelle or lipid bilayer of PEGylated liposome has a major effect on this phenomenon. These studies have significant implications for the evaluation of PEG-poly(L-lysine)-based micellar formulation of Gd-based contrast agents.

Tissue gadolinium deposition and fibrosis mimicking nephrogenic systemic fibrosis (NSF)-subclinical nephrogenic systemic fibrosis?

Nephrogenic systemic fibrosis is a condition with significant and often debilitating cutaneous manifestations. Recent research on this disease has delineated an association between nephrogenic systemic fibrosis and exposure to magnetic resonance imaging studies using gadolinium-based contrast agents in patients with ongoing renal failure. This metal has been detected in cutaneous biopsy specimens taken from lesional skin suggesting that gadolinium provides an impetus for the deposition of circulating fibrocytes in the skin and subsequent fibrosis. We describe a hemodialysis-dependent liver transplant recipient who received a gadolinium-based contrast agent and demonstrated insoluble gadolinium deposition in a fibrotic dermis and subcutaneous septum using scanning electron microscopy/energy dispersive x-ray spectroscopy. He has yet to manifest symptoms and signs of nephrogenic systemic fibrosis 3 years after his magnetic resonance imaging study.

Regulation of collagen turnover in human skin fibroblasts exposed to a gadolinium-based contrast agent

OBJECTIVE

Nephrogenic systemic fibrosis is a clinical syndrome linked with exposure in renal failure patients to gadolinium-based contrast agents (GBCAs) during magnetic resonance imaging. Recently, we demonstrated that GBCA exposure led to increased matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of metalloproteinases-1 (TIMP-1) levels in human skin fibroblasts. The goals of the present work were to assess the relationship between altered MMP-1/TIMP-1 expression and collagen production/deposition, and the intracellular signaling events that lead from GBCA stimulation to altered MMP-1 and TIMP-1 production.

MATERIALS AND METHODS

Human dermal fibroblasts were treated with one of the currently used GBCAs (Omniscan). Proliferation was quantified as were levels of MMP-1, TIMP-1, procollagen type I, and collagen type I. Signaling events were concomitantly assessed, and signaling inhibitors were used.

RESULTS

Fibroblasts exposed to Omniscan had increases in both MMP-1 and TIMP-1 levels. Omniscan treatment interfered with collagen turnover, leading to increased type I collagen deposition without an increase in type I procollagen production. U0126, an inhibitor of mitogen-activated protein kinase signaling, and LY294002, a phosphatidylinositol-3 kinase inhibitor, reduced MMP-1 levels. U0126 also reduced TIMP-1 levels, but LY294002 increased TIMP-1.

CONCLUSION

These data provide evidence for complex regulation of collagen deposition in Omniscan-treated skin. They suggest that the major effect of Omniscan exposure is on an enzyme/inhibitor system that regulates collagen breakdown rather than on collagen production, per se.

Localised heating of tumours utilising injectable magnetic nanoparticles for hyperthermia cancer therapy

This study reports an investigation of hyperthermia cancer therapy utilising an alternating magnetic field to induce a localised temperature increase on tumours by using injectable magnetic nanoparticles. In-vitro and in-vivo experiments represent the feasibility of hyperthermia cancer therapy. A feedback temperature control system was first developed to keep the nanoparticles at a constant temperature to prevent overheating in the tumours such that a safer and more precise cancer therapy becomes feasible. By using the feedback temperature control system, magnetic nanoparticles can be heated up to the specific constant temperatures, 37, 40, 42, 45, 46 and 47 degrees C, respectively, with a variation less than 0.2 degrees C. With this approach, the in-vitro survival rate of tumour cells at different temperatures can be systematically explored. It was experimentally found that the survival rate of cancer cells can be greatly reduced while CT-26 cancer cells were heated above 45 degrees C. Besides, localised temperatures increase as high as 59.5 degrees C can be successfully generated in rat livers by using the proposed method. Finally, complete regression of tumour was achieved. The developed method used injectable magnetic nanoparticles and may provide a promising approach for hyperthermia cancer therapy.

Nephrogenic systemic fibrosis and management of high-risk patients

The purpose of this work is to provide current information on the rapidly evolving subject of nephrogenic systemic fibrosis (NSF), to establish the radiologic approach to the management of high-risk patients for NSF, and to assess the probabilistic risk of NSF compared to contrast induced nephropathy (CIN), as encountered with iodinated contrast media used in computed tomographic (CT) imaging. NSF is a disease process of considerable concern following gadolinium-containing contrast agents (GCCA) exposure in patients with diminished renal function. To minimize the possibility of NSF development in high-risk patients, GGCAs should not be used when they are not necessary, or the GCCAs, that have not at present been associated with NSF development, should be used at the lowest possible diagnostic dose, when they are necessary. Contrast-induced nephropathy is also a great risk in this patient population following the adminstration of iodinated contrast media (CM). In patients with diminished renal function who are not on regular dialysis, the risk of CIN following the administration of iodinated CM is higher than the risk of NSF following the administration of the most stable GCCAs. Risk benefit analysis should be performed prior to the administration of all CM, and the best combination of safety and diagnostic accuracy should be sought. Concern of NSF or CIN should not prevent the use of contrast agents in magnetic resonance imaging or computed tomography when they are deemed essential.

Effects of gadolinium-based magnetic resonance imaging contrast agents on human skin in organ culture and human skin fibroblasts

OBJECTIVE

Nephrogenic systemic fibrosis (NSF) is a clinical syndrome linked with exposure in renal failure patients to gadolinium-based magnetic resonance imaging contrast agents (GBCAs). The pathogenesis of the disease is largely unknown. The present study addresses potential pathophysiological mechanisms.

MATERIALS AND METHODS

Here, we have examined human skin in organ culture and human dermal fibroblasts in monolayer culture for responses to GBCA stimulation.

RESULTS

Treatment of normal human skin in organ culture with Omniscan had no significant effect on type I procollagen but increased both matrix metalloproteinase-1 and tissue inhibitor of metalloproteinases-1. At the histologic level, many interstitial cells demonstrated cytologic features characteristic of activation (ie, light staining, oblong, plump nuclei). Omniscan, as well as 3 other magnetic resonance imaging contrast agents (Magnevist, Multihance, and Prohance), increased proliferation of human dermal fibroblasts in monolayer culture. Increased proliferation was accompanied by an increase in production of both matrix metalloproteinase-1 and tissue inhibitor of metalloproteinases-1 but no increase in type I procollagen. Concentrations required for effects differed among the 4 agents (Omniscan < Magnevist and Multihance < Prohance). In contrast to its effects on fibroblast function, Omniscan did not stimulate human epidermal keratinocyte proliferation when examined over a wide range of concentrations.

CONCLUSION

These data provide evidence that GBCA exposure in ex vivo skin from healthy individuals increases fibroblast proliferation and has effects on the enzyme/inhibitor system that regulates collagen turnover in the skin.

Contrast enhanced MR angiography with parallel imaging in the early period after renal transplantation

PURPOSE

To evaluate renal allograft vessels in the early period after kidney transplantation with three-dimensional (3D) contrast-enhanced MR angiography (3D CE MRA) using a parallel imaging technique.

MATERIALS AND METHODS

Sixty-three consecutive patients were examined with 3D CE MRA and integrated SENSE technique (Sensitivity Encoding) 2 to 21 days after renal transplantation. MR angiography studies were analyzed for the presence of arterial stenosis. The degree of renal transplant artery stenosis was graded qualitatively as <50% = mild, 50-70% = moderate, 70-99% = severe, and occlusion. Four patients (6.3%) with moderate (n = 1) or severe (n = 3) arterial stenoses on CE MRA underwent selective intra-arterial digital subtraction angiography. In two patients, selective intravenous digital subtraction angiography (DSA) was performed.

RESULTS

Twenty-seven (42.9%) of the 63 patients had normal CE MR angiograms, 29 (46%) showed mild, 3 patients (4.8%) moderate, and 4 patients (6.3%) severe stenoses of the donor artery. In three patients, the severe stenosis of the graft artery was confirmed by surgery or intra-arterial DSA. One patient with suspicion of severe arterial stenosis on MRA had moderate vessel narrowing on DSA. Twelve months after kidney transplantation, serum creatinine levels were not significantly different in patients with mild and moderate stenoses from those without (P > 0.19) but significantly different from those with severe stenoses (P < 0.05).

CONCLUSION

The incidence of mild and moderate vessel narrowing at the arterial anastomosis is unexpectedly high in the early period after kidney transplantation and is most likely due to surgery-related tissue edema.

Discrepancies between the fate of myoblast xenograft in mouse leg muscle and NMR label persistency after loading with Gd-DTPA or SPIOs

1H-NMR (nuclear magnetic resonance) imaging is regularly proposed to non-invasively monitor cell therapy protocols. Prior to transplantation, cells must be loaded with an NMR contrast agent (CA). Most studies performed so far make use of superparamagnetic iron oxide particles (SPIOs), mainly for favorable detection sensitivity. However, in the case of labeled cell death, SPIO recapture by inflammatory cells might introduce severe bias. We investigated whether NMR signal changes induced by preloading with SPIOs or the low molecular weight gadolinium (Gd)-DTPA accurately monitored the outcome of transplanted cells in a murine model of acute immunologic rejection. CA-loaded human myoblasts were grafted in the tibialis anterior of C57BL/6 mice. NMR imaging was repeated regularly until 3 months post-transplantation. Label outcome was evaluated by the size of the labeled area and its relative contrast to surrounding tissue. In parallel, immunohistochemistry assessed the presence of human cells. Data analysis revealed that CA-induced signal changes did not strictly reflect the graft status. Gd-DTPA label disappeared rapidly yet with a 2-week delay compared with immunohistochemical evaluation. More problematically, SPIO label was still visible after 3 months, grossly overestimating cell survival (<1 week). SPIOs should be used with extreme caution to evaluate the presence of grafted cells in vivo and could hardly be recommended for the long-term monitoring of cell transplantation protocols.

Magnetic resonance imaging in patients with meningitis induced hearing loss

The aim of this multicentre study was to compare T1 with T2 weighted MRI scans of the labyrinth after meningitis and to investigate whether waiting with scanning improved the reliability of diagnosing an ongoing process such as cochlear osteogenesis. Forty-five patients were included who suffered from meningitis induced hearing loss (radiological imaging <1 year after meningitis). Twenty-one gadolinium enhanced T1 and 45 T2 weighted MRI scans were scored by two radiologists regarding the condition of the labyrinth. These radiological observations were compared with the condition of the cochlea as described during cochlear implantation. A higher percentage of agreement with surgery was found for T2 (both radiologists 73%) than for T1 weighted MRI scans (radiologist 1: 62%, radiologist 2: 67%), but this difference is not significant. There was no significant difference between early (0–3 months) and late (>3 months) scanning, showing that radiological imaging soon after meningitis allows early diagnosis without suffering from a lower agreement with surgical findings.

Prevalence of nephrogenic systemic fibrosis in renal insufficiency patients: results of the FINEST study

PURPOSE

Nephrogenic systemic fibrosis (NSF) is characterized by widespread tissue fibrosis, mainly affecting the skin. Gadolinium chelates have been implicated in the onset of NSF in patients with renal impairment (RI). The FINEST study (FIbrose Néphrogénique SysTémique) was designed to determine the prevalence of NSF after magnetic resonance imaging (MRI) in French RI patients.

MATERIALS AND METHODS

We studied all patients with RI who had at least one MRI examination during a one-year period, with or without gadolinium chelate administration. Data were collected retrospectively from 9 Nephrology Departments in France, and included sex, age, renal function, type of gadolinium administered, and subsequent cutaneous disorders. If a patient presented a cutaneous disorder, a skin biopsy was performed to confirm the diagnostic.

RESULTS

The 308 eligible patients had a mean age of 59.9 years, 59% were men, and 54% had stage 5 RI. 75% of those 308 patients received a Gadolinium chelate. Among those patients who received a gadolinium chelate, 76% received gadoterate, 20% gadopentetate, 3% gadodiamide and 1% gadobenate. No cutaneous disorders were recorded after MRI.

CONCLUSION

These results confirm that NSF is a rare disease. Based on a reported frequency, approximately 3.5% in patients with glomerular filtration rate <30ml/min/1.73m(2)), some cases should have been observed in our study which included 308 patients. Most patients received gadoterate, a macrocyclic gadolinium chelate for which no case of NSF has been observed worldwide. This suggests that more stable macrocyclic agents may be less likely to induce NSF.

MR imaging in patients at risk for developing nephrogenic systemic fibrosis: protocols, practices, and imaging techniques to maximize patient safety

Nephrogenic systemic fibrosis (NSF) is a rare but potentially debilitating or even fatal fibrosing condition that most often affects the skin but is now also recognized to involve multiple organs. The first report on NSF was published in 1997, and there is mounting evidence that this condition is associated with renal failure and the administration of large amounts of gadolinium. Although gadolinium-enhanced magnetic resonance (MR) imaging was once considered one of the safer imaging procedures, concerns over NSF have led the radiology community to rethink its imaging practices. Several noncontrast angiographic techniques based on fast spin-echo, gradient-echo, phase-contrast, and inversion-recovery principles are currently available. These techniques allow MR angiography to be performed safely, even in patients at risk for developing NSF. When use of gadolinium-based contrast material is necessary for diagnosis, it is possible to reduce total gadolinium administration through the use of agents with higher relaxivity, time-resolved imaging, high-field-strength magnets, and body compression devices. Management of NSF also requires an understanding of the risk factors of this disease and developing an institutional policy for identifying and testing at-risk patients.

Time-resolved contrast-enhanced MR angiography of intracranial lesions

PURPOSE

To determine if contrast-enhanced (CE) MRI of intracranial lesions benefits from time-resolved MR angiography (MRA) during contrast agent injection.

MATERIALS AND METHODS

For 126 patients with suspected intracranial lesions undergoing routine CE MRI at 3.0T (N = 88) or 1.5T (N = 38), time-resolved CE MRA (three-dimensional [3D] time-resolved imaging of contrast kinetics [TRICKS]) was performed during injection of the routine gadolinium (Gd) dose of 0.1 mmol/kg. Time to peak (TTP) enhancement of lesions as well as time to internal carotid artery (ICA), middle cerebral artery (MCA), superior sagittal sinus (SSS), and jugular vein enhancement were measured. Source and maximum intensity projection (MIP) images were reviewed to delineate the spatial relationship of lesions and the vasculature.

RESULTS

In 61 patients (48%), additional important findings were detected on time-resolved MRA that were not seen on the routine CE protocol, including aneurysms (N = 6), arteriovenous malformations (N = 7), ICA stenoses (N = 2), vascular anomalies (N = 18), and relationships between lesions and vessels (N = 28). In addition, tumor TTP correlated with glioma grade (r = 0.87) and discriminated epithelial from nonepithelial meningiomas (P = 2.6 x 10(-5)). MRA added eight minutes to the total exam time.

CONCLUSION

Time-resolved MRA performed during contrast agent injection adds information to the routine brain CE MRI examination of intracranial lesions with only a small time penalty and no additional risk to the patient.

Chemistry of paramagnetic and diamagnetic contrast agents for Magnetic Resonance Imaging and Spectroscopy pH responsive contrast agents

We provide a brief overview of the chemistry and most relevant properties of paramagnetic and diamagnetic contrast agents (CAs) for Magnetic Resonance Imaging and Magnetic Resonance Spectroscopic Imaging. Paramagnetic CAs for MRI consist mainly of Gd(III) complexes from linear or macrocyclic polyaminopolycarboxylates. These agents reduce, the relaxation times T(1) and T(2) of the water protons in a concentration dependent manner, increasing selectively MRI contrast in those regions in which they accumulate. In most instances they provide anatomical information on the localization of lesions and in some specific cases they may allow to estimate some physiological properties of tissues including mainly vascular performance. Because of its ability to discriminate easily between normal and diseased tissue, extracellular pH (pH(e)) has been added recently, to the battery of variables amenable to MRI investigation. A variety of Gd(III) containing macrocycles sensitive to pH, endogenous or exogenous polypeptides or even liposomes have been investigated for this purpose, using the pH dependence of their relaxivity or magnetization transfer rate constant (chemical exchange saturation transfer, CEST). Many environmental circumstances in addition to pH affect, however, relaxivity or magnetization transfer rate constants of these agents, making the results of pH measurements by MRI difficult to interpret. To overcome these limitations, our laboratory synthesized and developed a novel series of diamagnetic CAs for Magnetic Resonance Spectroscopic Imaging, a new family of monomeric and dimeric imidazolic derivatives able to provide unambiguous measurements of pH(e), independent of water relaxivity, diffusion or exchange.

Synthesis, characterization, and in vitro testing of superparamagnetic iron oxide nanoparticles targeted using folic Acid-conjugated dendrimers

Organic-coated superparamagnetic iron oxide nanoparticles (OC-SPIONs) were synthesized and characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. OC-SPIONs were transferred from organic media into water using poly(amidoamine) dendrimers modified with 6-TAMRA fluorescent dye and folic acid molecules. The saturation magnetization of the resulting dendrimer-coated SPIONs (DC-SPIONs) was determined, using a superconducting quantum interference device, to be 60 emu/g Fe versus 90 emu/g Fe for bulk magnetite. Selective targeting of the DC-SPIONs to KB cancer cells in vitro was demonstrated and quantified using two distinct and complementary imaging modalities: UV-visible and X-ray fluorescence; confocal microscopy confirmed internalization. The results were consistent between the uptake distribution quantified by flow cytometry using 6-TAMRA UV-visible fluorescence intensity and the cellular iron content determined using X-ray fluorescence microscopy.

Gadolinium(III) complexes as MRI contrast agents: ligand design and properties of the complexes

Magnetic resonance imaging is a commonly used diagnostic method in medicinal practice as well as in biological and preclinical research. Contrast agents (CAs), which are often applied are mostly based on Gd(III) complexes. In this paper, the ligand types and structures of their complexes on one side and a set of the physico-chemical parameters governing properties of the CAs on the other side are discussed. The solid-state structures of lanthanide(III) complexes of open-chain and macrocyclic ligands and their structural features are compared. Examples of tuning of ligand structures to alter the relaxometric properties of gadolinium(III) complexes as a number of coordinated water molecules, their residence time (exchange rate) or reorientation time of the complexes are given. Influence of the structural changes of the ligands on thermodynamic stability and kinetic inertness/lability of their lanthanide(III) complexes is discussed.

Extracellular gadolinium-based contrast media: an overview

Increasing use is made of extracellular MRI contrast agents that alter the image contrast following intravenous administration; they predominantly shorten the T1 relaxation time of tissues. The degree and location of these changes provide substantial diagnostic information. However gadolinium-based contrast agents (Gd-CA) are not inert drugs. They may cause acute non-renal adverse reactions (e.g. anaphylactoid reactions), acute renal adverse reactions (e.g. contrast induced nephropathy), delayed adverse reactions (nephrogenic systemic fibrosis) and problems at the site of injection (e.g. local necrosis). This review describes the current status of Gd-CA, their mechanism of action, chemical structure, pharmacokinetics, dosage, elimination, nephrotoxicity and adverse events.

Biochemical safety profiles of gadolinium-based extracellular contrast agents and nephrogenic systemic fibrosis

Gadolinium (Gd)-based paramagnetic contrast agents are relatively safe when used in clinically recommended doses. However, with the rapidly expanding body of literature linking Gd-based paramagnetic contrast agents and nephrogenic systemic fibrosis (NSF), awareness of the potential side effects and adverse reactions from Gd is now an important requirement for practicing radiologists. In addition to the ongoing accumulation and analyses of clinical NSF data, it is also essential for the practicing radiologist to understand the biochemical characteristics of the extracellular Gd-chelates. The purpose of this review is to consolidate and update the available information on known side effects, adverse reactions, and toxicity of the Gd chelates, with particular emphasis on the potential mechanisms of NSF.

Urinary sodium dodecyl sulfate electrophoresis with silver staining: a noninvasive diagnostic tool for obstructive uropathy in children

PURPOSE

Obstructive uropathy such as ureteropelvic junction obstruction in the newborn is a major diagnostic and therapeutic dilemma. We investigated whether urinary sodium dodecyl sulfate electrophoresis with polyacrylamide gel electrophoresis with silver staining could be used to discriminate between children requiring and those not requiring pyeloplasty.

MATERIALS AND METHODS

In a pilot study we analyzed the urine of 18 children (mean age 2.7 years) with grade III or IV hydronephrosis according to the Society for Fetal Urology classification. A total of 44 healthy children were studied as controls. Children with hydronephrosis were followed using ultrasound, (99m)technetium mercaptoacetyltriglycine diuretic renography and voiding cystourethrography. Urine was obtained by spontaneous voiding and studied by sodium dodecyl sulfate polyacrylamide gel electrophoresis with silver staining using Melzer's modification. After the study period test results were compared to outcomes, ie whether patients required surgery, and to normalization of previously abnormal protein excretion patterns.

RESULTS

All but 1 of the healthy controls had a normal electrophoresis assessment. Of 9 patients followed for hydronephrosis 7 had an abnormal electrophoresis result preoperatively. One child had to be operated on twice because of relapse of ureteropelvic junction obstruction. Six children returned to a normal electrophoresis result postoperatively, including the child who was operated on twice. All children with an initially normal electrophoresis assessment displayed persistent normal values, except 1. Children shifting from a normal to an abnormal electrophoresis result underwent surgery after exclusion of urinary tract infection.

CONCLUSIONS

Sodium dodecyl sulfate polyacrylamide gel electrophoresis with silver staining seems to be a good predictive test for clinically relevant ureteropelvic junction obstruction. Further studies are being performed to see whether the test can stand against the gold standard, (99m)technetium mercaptoacetyltriglycine diuretic renography.

MR-guided endovascular interventions: a comprehensive review on techniques and applications

The magnetic resonance (MR) guidance of endovascular interventions is probably one of the greatest challenges of clinical MR research. MR angiography is not only an imaging tool for the vasculature but can also simultaneously depict high tissue contrast, including the differentiation of the vascular wall and perivascular tissues, as well as vascular function. Several hurdles had to be overcome to allow MR guidance for endovascular interventions. MR hardware and sequence design had to be developed to achieve acceptable patient access and to allow real-time or near real-time imaging. The development of interventional devices, both applicable and safe for MR imaging (MRI), was also mandatory. The subject of this review is to summarize the latest developments in real-time MRI hardware, MRI, visualization tools, interventional devices, endovascular tracking techniques, actual applications and safety issues.