Necrosis-avid Contrast Agents Research Articles

In Vivo Evaluation of Gallium-68-Labeled IRDye800CW as a Necrosis Avid Contrast Agent in Solid Tumors.

Necrosis only occurs in pathological situations and is directly related to disease severity and, therefore, is an important biomarker. Tumor necrosis occurs in most solid tumors due to improperly functioning blood vessels that cannot keep up with the rapid growth, especially in aggressively growing tumors. The amount of necrosis per tumor volume is often correlated to rapid tumor proliferation and can be used as a diagnostic tool. Furthermore, efficient therapy against solid tumors will directly or indirectly lead to necrotic tumor cells, and detection of increased tumor necrosis can be an early marker for therapy efficacy. We propose the application of necrosis avid contrast agents to detect therapy-induced tumor necrosis. Herein, we advance gallium-68-labeled IRDye800CW, a near-infrared fluorescent dye that exhibits excellent necrosis avidity, as a potential PET tracer for in vivo imaging of tumor necrosis. We developed a reliable labeling procedure to prepare [68Ga]Ga-DOTA-PEG4-IRDye800CW ([68Ga]Ga-1) with a radiochemical purity of >96% (radio-HPLC). The prominent dead cell binding of fluorescence and radioactivity from [68Ga]Ga-1 was confirmed with dead and alive cultured 4T1-Luc2 cells. [68Ga]Ga-1 was injected in 4T1-Luc2 tumor-bearing mice, and specific fluorescence and PET signal were observed in the spontaneously developing tumor necrosis. The ip injection of D-luciferin enabled simultaneous bioluminescence imaging of the viable tumor regions. Tumor necrosis binding was confirmed ex vivo by colocalization of fluorescence uptake with TUNEL dead cell staining and radioactivity uptake in dichotomized tumors and frozen tumor sections. Our presented study shows that [68Ga]Ga-1 is a promising PET tracer for the detection of tumor necrosis.

In Vivo Evaluation of Indium-111\u2013Labeled 800CW as a Necrosis-Avid Contrast Agent

PurposeCurrent clinical measurements for tumor treatment efficiency rely often on changes in tumor volume measured as shrinkage by CT or MRI, which become apparent after multiple lines of treatment and pose a physical and psychological burden on the patient. Detection of therapy-induced cell death in the tumor can be a fast measure for treatment efficiency. However, there are no reliable clinical tools for detection of tumor necrosis. Previously, we studied the necrosis avidity of cyanine-based fluorescent dyes, which suffered long circulation times before tumor necrosis could be imaged due to low hydrophilicity. We now present the application of radiolabeled 800CW, a commercially available cyanine with high hydrophilicity, to image tumor necrosis in a mouse model.ProceduresWe conjugated 800CW to DOTA via a PEG linker, for labeling with single-photon emission-computed tomography isotope indium-111, yielding [111In]In-DOTA-PEG4-800CW. We then investigated specific [111In]In-DOTA-PEG4-800CW uptake by dead cells in vitro, using both fluorescence and radioactivity as detection modalities. Finally, we investigated [111In]In-DOTA-PEG4-800CW uptake into necrotic tumor regions of a 4T1 breast tumor model in mice.ResultsWe successfully prepared a precursor and developed a reliable procedure for labeling 800CW with indium-111. We detected specific [111In]In-DOTA-PEG4-800CW uptake by dead cells, using both fluorescence and radioactivity. Albeit with a tumor uptake of only 0.37%ID/g at 6 h post injection, we were able to image tumor necrosis with a tumor to background ratio of 7:4. Fluorescence and radioactivity in cryosections from the dissected tumors were colocalized with tumor necrosis, confirmed by TUNEL staining.Conclusions[111In]In-DOTA-PEG4-800CW can be used to image tumor necrosis in vitro and in vivo. Further research will elucidate the application of [111In]In-DOTA-PEG4-800CW or other radiolabeled hydrophilic cyanines for the detection of necrosis caused by chemotherapy or other anti-cancer therapies. This can provide valuable prognostic information in treatment of solid tumors.

Rhein-based necrosis-avid MRI contrast agents for early evaluation of tumor response to microwave ablation therapy.

Early evaluation of tumor response to thermal ablation therapy can help identify untreated tumor cells and then perform repeated treatment as soon as possible. The purpose of this work was to explore the potential of rhein-based necrosis-avid contrast agents (NACAs) for early evaluation of tumor response to microwave ablation (MWA). 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay was performed to test the cytotoxicity of rhein-based NACAs against HepG2 cells. Rat models of liver MWA were used for investigating the effectiveness of rhein-based NACAs in imaging the MWA lesion, the optimal time period for post-MWA MRI examination, and the metabolic behaviors of 68 Ga-labeled rhein-based NACAs. Rat models of orthotopic liver W256 tumor MWA were used for investigating the time window of rhein-based NACAs for imaging the MWA lesion, the effectiveness of these NACAs in distinguishing the residual tumor and the MWA lesion, and their feasibility in early evaluating the tumor response to MWA. Gadolinium 2,2',2''-(10-(2-((4-(4,5-Dihydroxy-9,10-dioxo-9,10-dihydroanthracene-2-carboxamido)butyl)amino)-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (GdL2 ) showed low cytotoxicity and high quality in imaging the MWA region. The optimal time period for post-MWA MRI examination using GdL2 was 2 to 24 h after the treatment. During 2.5 to 3.5 h postinjection, GdL2 can better visualize the MWA lesion in comparison with gadolinium 2-[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododec-1-yl]acetic acid (Gd-DOTA), and the residual tumor would not be enhanced. The tumor response to MWA as evaluated by using GdL2 -enhanced MRI was consistent with histological examination. GdL2 appears to be a promising NACA for the tumor response assessment after thermal ablation therapies.

Necrosis Avidity: A Newly Discovered Feature of Hypericin and its Preclinical Applications in Necrosis Imaging

Hypericin has been widely studied as a potent photosensitizer for photodynamic therapy in both preclinical and clinical settings. Recently, hypericin has also been discovered to have a specific avidity for necrotic tissue. This affinity is also observed in a series of radiolabeled derivatives of hypericin, including [123I]iodohypericin, [124I]iodohypericin, and [131I]iodohypericin. Hypericin, along with other necrosis-avid contrast agents, has been investigated for use in noninvasively targeting necrotic tissues in numerous disorders. Potential clinical applications of hypericin include the identification of acute myocardial infarction, evaluation of tissue viability, assessment of therapeutic responses to treatments, and interventional procedures for solid tumors. The mechanisms of necrosis avidity in hypericin remain to be fully elucidated, although several hypotheses have been suggested. In particular, it has been proposed that the necrosis avidity of hypericin is compound specific; for instance, cholesterol, phosphatidylserine, or phosphatidylethanolamine components in the phospholipid bilayer of cellular membranes may be the major targets for its observed selectivity. Further investigations are needed to identify the specific binding moiety that is responsible for the necrosis avidity of hypericin.

Development, evaluation and application of reperfused liver infarction in rats as a practical model for studying ischemic diseases and screening new drugs

Appropriate animal models of human diseases often lead to important discoveries in biomedical sciences. An animal model of reperfused liver infarction (RLI) in rats has been introduced and applied originally as an easier substitute of brain and heart infarction for developing necrosis-avid contrast agents (NACAs) to enhance the sensitivity and specificity of magnetic resonance imaging (MRI) in diagnosis of ischemic cardiovascular diseases such as acute myocardial infarction and stroke and in the assessment of certain tissue destroying therapies. The ever-advancing MRI technology has enabled comprehensive in vivo non-invasive characterisation of this model to gain further insight into its morphological and functional specifications and to implicate its broader utilities for preclinical developments of new diagnostics and therapeutics. The in vivo MRI outcomes have been further validated by postmortem microangiography and histology. The present mini review article aims to highlight a number of relevant aspects about the RLI model in rats and to facilitate those interested academic or industrial researchers to apply this model in their own experimental studies.

Metalloporphyrins and Functional Analogues as MRI Contrast Agents

Following the footprint of porphyrin-mediated photodynamic therapy (PDT), paramagnetic metalloporphyrins were originated as tumor seeking contrast agents (CAs) for magnetic resonance imaging (MRI). However, serial research has disproved their tumor selectivity, identified nonviable tissues as their real targets, and eventually elicited new applica- tions in myocardial infarction delineation, tissue viability evaluation, ablation therapy assessment, as well as first pass or dynamic perfusion MRI, multi-organ contrast enhancement (CE), atherosclerotic plaque imaging and stem cell labeling or tracking. Furthermore, nonporphyrin analogues have been developed to reduce porphyrin related toxicities. These porphy- rin and nonporphyrin compounds have been termed as necrosis-avid contrast agents (NACAs) to denote their major dis- covered affinity. The present review aims to document the evolving research in this particular field, to discuss possible mechanisms, to promote further preclinical and clinical development of this unique and promising class of MRI CAs, and to implicate a novel stroma targeting strategy for diagnosis and treatment of malignant and benign disorders.

Exploration of the mechanism underlying the tumor necrosis avidity of hypericin

Hypericin, a potent necrosis avid agent, features a peculiar affinity for necrotic tissue. Necrosis avid contrast agents have been investigated as markers for non-invasive imaging of different disorders. In view of the promising clinical applications, a more complete knowledge of the mechanism of action is important for the future development of new chemical structures with improved characteristics. To study whether a compound-specific or non-specific mechanism based on plasma lipoprotein transport is involved in the accumulation of hypericin in intratumoral necrosis, we performed a visual and quantitative fluoromicroscopic analysis of the colocalization of hypericin and DiOC18-labeled lipoproteins in subcutaneous murine radiation-induced fibrosarcoma tumors. Microscopic fluorescent overlay images of necrotic tumors demonstrated that hypericin already showed clear necrosis avid characteristics 4 h after injection, whereas a similar outstanding accumulation in necrosis was not demonstrated for the labeled lipoproteins. Moreover, a quantitative analysis of fluoromicroscopic images of tumor necrosis at 24 h after injection showed differences in normalized fluorescence intensities between hypericin and labeled lipoproteins of 50-100%, reflecting a shifted pattern in localization. We conclude that our results are indicative of a release of hypericin from the lipoprotein complex at some point along its way through the peri-necrotic tumor area and the necrotic tissue debris, which is in line with the hypothesis of a compound-specific mechanism.

CMR 2007: 1.06: Necrosis avid contrast agents: evidence in favor of hypothetical mechanisms and new potential applications

CMR 2007: 1.06: Necrosis avid contrast agents: evidence in favor of hypothetical mechanisms and new potential applications

MRI with necrosis-avid contrast agent for the assessment of myocardial viability in a swine model

目的 通过冠状动脉注射坏死组织亲和性非卟啉类顺磁性对比剂(ECⅢ-60)后MR延时影像与病理对照的方法明确其强化区与梗死心肌的关系,并与静脉注射非特异性对比剂钆喷替酸葡甲胺(Gd-DTPA)比较,以期为MRI准确评价心肌活性提供可靠的病理依据.方法 经导管采用闭胸法成功建立8只猪的急性心肌梗死再灌注模型.经静脉以0.2 mmol/kg快速团注Gd-DTPA后行心电激发的心脏MR短轴面T1WI,延时扫描至局部Gd-DTPA完全消失.然后再以0.0025 mmol/kg经冠状动脉导管缓慢注入ECⅢ-60后短轴面T1WI,延时成像至5 h.比较分析ECⅢ-60增强MRI延时强化区和金标准病理所示梗死区的关系;并和Gd-DTPA增强MRI的对比增强效果(CR)与范围(RIS)进行比较.结果 ECⅢ-60增强MRI可见梗死区的信号较正常对照区明显升高(CR＞3.0)并持续超过5 h,其强化区相对面积[占同层面左室面积的百分率为(11.84±3.63)%]与TTC染色心肌梗死面积[(11.78±3.64)%]一致(t=2.251,P＞0.05),两者呈正相关,其决定系数为r=0.999.Gd-DTPA也能产生CR＞3.0的强化效果,但对梗死区的对比度在2 h内逐步消失.结论 坏死亲和性对比剂增强MRI能持续准确地反映心肌梗死,能成为冠状动脉介入术后心肌活力评估的有潜在价值的方法。

Magnetic Resonance Imaging of Acute Reperfused Myocardial Infarction: Intraindividual Comparison of ECIII-60 and Gd-DTPA in a Swine Model

To compare a necrosis-avid contrast agent (NACA) bis-Gd-DTPA-pamoic acid derivative (ECIII-60) after intracoronary delivery with an extracellular agent Gd-DTPA after intravenous injection on magnetic resonance imaging (MRI) in a swine model of acute reperfused myocardial infarction (MI). Eight pigs underwent 90 min of transcatheter coronary balloon occlusion and 60 min of reperfusion. After intravenous injection of Gd-DTPA at a dose of 0.2 mmol/kg, all pigs were scanned with T1-weighted MRI until the delayed enhancement of MI disappeared. Then they were intracoronarily infused with ECIII-60 at 0.0025 mmol/kg and imaged for 5 hr. Signal intensity, infarct-over-normal contrast ratio and relative infarct size were quantified, compared, and correlated with the results of postmortem MRI and triphenyltetrazolium chloride (TTC) histochemical staining. A contrast ratio over 3.0 was induced by both Gd-DTPA and ECIII-60. However, while the delayed enhancement with Gd-DTPA virtually vanished in 1 hr, ECIII-60 at an 80x smaller dose depicted the MI accurately over 5 hr as proven by ex vivo MRI and TTC staining. Both Gd-DTPA and ECIII-60 strongly enhanced acute MI. Comparing with fading contrast in a narrow time window with intravenous Gd-DTPA, intracoronary ECIII-60 persistently demarcated the acute MI, indicating a potential method for postprocedural assessment of myocardial viability after coronary interventions.

Magnetic resonance imaging after radiofrequency ablation in a rodent model of liver tumor: tissue characterization using a novel necrosis-avid contrast agent

We exploited a necrosis-avid contrast agent ECIV-7 for magnetic resonance imaging (MRI) in rodent liver tumors after radiofrequency ablation (RFA). Rats bearing liver rhabdomyosarcoma (R1) were randomly allocated to three groups: group I, complete RFA, group II, incomplete RFA, and group III, sham ablation. Within 24 h after RFA, T1-weighted (T1-w) MRI was performed before and after injection of ECIV-7 at 0.05 mmol/kg and followed up from 6-24 h. Signal intensities (SIs) were measured with relative enhancement (RE) and contrast ratio (CR) calculated. The MRI findings were verified histomorphologically. On plain T1-w MRI the contrasts between normal liver, RFA lesion, residual and/or intact tumor were vague. Early after administration of ECIV-7, the liver SI was strongly enhanced (RE=40-50%), leaving the RFA lesion as a hypointense region in groups I and II. At delayed phase, two striking peri-ablational enhancement patterns appeared (RE=90% and CR=1.89%), i.e., "O" type of hyperintense rim in group I and "C" type of incomplete rim in group II. These MRI manifestations could be proven histologically. In this study, tissue components after RFA could be characterized with discernable contrasts by necrosis-avid contrast agent (NACA)-enhanced MRI, especially at delayed phase. This approach may prove useful for defining the ablated area and identifying residual tumor after RFA.

Necrosis Avid Contrast Agents

Two categories of necrosis-avid contrast agents (NACAs), namely porphyrin- and nonporphyrin-based complexes, have thus far been discovered as necrosis-targeting markers for noninvasive magnetic resonance imaging (MRI) identification of acute myocardial infarction, assessment of tissue or organ viability, and therapeutic evaluation after interventional therapies. In addition to necrosis labeling, other less-specific functions, such as first-pass perfusion, blood pool contrast effect, hepatobiliary contrast enhancement (CE), adrenal and spleen CE, and renal functional imaging, also are demonstrated with NACAs. Despite various investigations with a collection of clues in favor of certain hypotheses, the mechanisms of such a unique targetability for NACAs still remain to be elucidated. However, a few things have become clear that porphyrin-like structures are not necessary for necrosis avidity and the albumin binding is not the supposed driving force but only a parallel nonspecific feature shared by both NACAs and non-NACA substances. Although the research and development of NACAs still remain in preclinical stage at a relatively small scale, their significance rests upon striking enhancement effects, which may warrant their eventual versatile clinical applications. The present review article is intended to summarize the cumulated facts about the evolving research on this topic, to demonstrate experimental observations for better understanding of the mechanisms, to trigger broader public interests and more intensive research activities, and to advocate, toward both academics and industries, further promotion of preclinical and clinical development of this unique and promising class of contrast agents.

Research on Necrosis Avid Contrast Agents: Further Expansion of Scope

Following discoveries of porphyrin and nonporphyrin necrosis-avid contrast agents (NACAs), their great potentialities for myocardial viability determination and therapeutic assessment have been recognized during multiinstitutional studies. The mechanisms of NACAs are currently under investigation. While the albumin binding was disproved as a key action, a physicochemical interaction between denatured tissue debris and chemicals of a wild range is hypothesized. In an effort to gain further insight into the mechanisms, the present experiments were conducted.

Synthesis, Characterization, and Pharmacokinetic Evaluation of a Potential MRI Contrast Agent Containing Two Paramagnetic Centers with Albumin Binding Affinity

A dinuclear gadolinium(III) complex of an amphiphilic chelating ligand, containing two diethylenetriamine-N,N,N',N'',N''-pentaacetate (DTPA) moieties bridged by a bisindole derivative with three methoxy groups, has been synthesized and evaluated as a potential magnetic resonance imaging (MRI) contrast agent. Nuclear magnetic relaxation dispersion (NMRD) measurements indicate that at 20 MHz and 37 degrees C the dinuclear gadolinium(III) complex has a much higher relaxivity than [Gd(DTPA)] (6.8 vs 3.9 s(-1) mmol(-1)). The higher relaxivity of the dinuclear gadolinium(III) complex can be related to its reduced motion and larger rotational correlation time relative to [Gd(DTPA)]. In the presence of human serum albumin (HSA) the relaxivity value of the noncovalently bound dinuclear complex increases to 15.2 s(-1) per mmol of Gd3+, due to its relatively strong interaction with this protein. The fitted value of the binding constant to HSA (Ka) was found to be 10(4) M(-1). Because of its interaction with HSA, the dinuclear complex exhibits a longer elimination half-life from the plasma, and a better confinement to the vascular space compared to the commercially available [Gd(DTPA)] contrast agent. Transmetalation of the dinuclear gadolinium(III) complex by zinc(II) has been investigated. Biodistribution studies suggest that the complex is excreted by the renal pathway, and possibly by the hepatobiliary route. In vivo studies indicated that half of the normal dose of the gadolinium(III) complex enhanced the contrast in hepatic tissues around 40 % more effectively than [Gd(DTPA)]. The dinuclear gadolinium(III) complex was tested as a potential necrosis avid contrast agent (NACA), but despite the binding to HSA, it did not exhibit necrosis avidity, implying that binding to albumin is not a key parameter for necrosis-targeting properties.

Detection and quantification of breast tumor necrosis with MR imaging: value of the necrosis-avid contrast agent Gadophrin-3.

The authors evaluated the use of T1-weighted magnetic resonance (MR) imaging with Gadophrin-3 enhancement and of plain T2-weighted MR imaging to detect and quantify breast tumor necrosis. Twenty EMT-6 tumors (mouse mammary sarcoma), implanted into the mammary fat pad of BALB/c-AnNCrl mice, underwent MR imaging with plain T2-weighted and T1-weighted fast field echo sequences before and 24 hours after injection of Gadophrin-3, a new necrosis-avid contrast agent. Tumor necrosis on MR images was quantified by means of a dedicated segmentation program and was correlated with histologic findings. In all tumors a central necrosis was revealed by histopathologic analysis, and central enhancement was seen with Gadophrin-3 on T1-weighted images. Small tumors (diameter, < 1 cm) showed an inhomogeneous central enhancement, whereas larger tumors (diameter, > 1 cm) enhanced mainly in the periphery of necrotic tissue. Plain T2-weighted images showed a hyperintense central area in only three of 20 cases with a large central necrosis. Gadophrin-3-enhanced T1-weighted images are superior to plain T2-weighted images for the detection of necrosis in a murine tumor xenograft model.

Exploring Multifunctional Features of Necrosis Avid Contrast Agents

As demonstrated during previous CMR meetings, some porphyrin (e.g. Gadophrin-2) and non-porphyrin (e.g. CEIII-60) paramagnetic chelates are able to specifically accumulate in nonviable tissues and can be applied for contrast-enhanced MRI of acute myocardial infarction and therapeutic necrosis (1–3). These molecules have therefore been defined as necrosis-avid contrast agents or NACAs under the category of a unique pathological targetability (3,4). The potential role of NACAs in imaging diagnosis has been recognized after multi-institutional reproducibility studies (5–21). Since NACAs also bear other common properties including early systemic distribution, albumin binding, hepatocellular uptake and renal elimination, we hypothesized that besides necrosis specificity, these agents can also be exploited for multipurpose applications. The present experiments have been conducted to evaluate the potentials of NACAs as “all-in-one” T1-relaxivity enhancers in comparison with other existing nonspecific and specific agents such as extracellular agent Gd-DTPA, hepatobiliary agent Mn-DPDP and albumin-binding blood pool agent MP-2269. MATERIALS AND METHODS

Intracoronary delivery of Gd-DTPA and Gadophrin-2 for determination of myocardial viability with MR imaging

The aim of this study was to compare intracoronary (i.c.) administration of Gadophrin-2, a necrosis-avid contrast agent (NACA), and nonspecific agent Gd-DTPA for determination of myocardial viability (MV) in acute myocardial infarction (AMI) with MRI. Reperfused AMI was induced in 12 dogs by transcatheter balloon occlusion of coronary artery. In 6 dogs each, Gd-DTPA at 0.1 mmol/kg or Gadophrin-2 at 0.005 mmol/kg was administered into coronary artery by fast bolus (n = 3) or slow infusion (n = 3). Serial ECG-triggered cardiac MRI of T1-weighted segmented turbo fast low-angle shot (FLASH) sequence was conducted and compared with triphenyltetrazolium chloride (TTC) histochemical staining. The contrast ratio and infarct size were quantified and analysed statistically. No cardiovascular side effects were found with local delivery of both agents. After i.c. administration, Gadophrin-2 induced a strong (CR > or = 1.78) and persistent (> or = 10 h) contrast enhancement of infarcted region. The infarct size defined with Gadophrin-2 was almost identical to that with TTC staining throughout the postcontrast period. With a dose 20 times higher, Gd-DTPA also strongly enhanced infarct-to-normal contrast; however, the enhancement diminished with time, i.e. from early strong to later faint enhancement and eventual loss of contrast. The delineated infarct size was also unstable, i.e. from early overestimation to later underestimation and eventual disappearance of the enhanced infarct. In combination with PTCA procedure, i.c. administration of MRI contrast agents may prove useful for post-procedure verification of diagnosis. The NACA-enhanced MRI may serve as an in vivo surrogate of postmortem histochemical staining for determination of MV. Although applicable in clinical setting, cardiac MRI with nonspecific Gd-DTPA is less reliable and should be performed within less than 1 h after contrast.

MRI contrast enhancement of necrosis by MP-2269 and gadophrin-2 in a rat model of liver infarction.

The mechanisms of action leading to specific localization of necrosis-avid contrast agents (NACAs) such as gadophrin-2 are not well defined. It has been suggested recently that agents with a high degree of serum albumin binding may also serve as NACAs by virtue of nonspecific hydrophobic interactions. The present MRI-histomorphology correlation study was conducted to verify the likelihood of the proposed albumin-binding mechanism by comparing an albumin-binding blood pool agent, MP-2269, with gadophrin-2 in a rat model of reperfused liver infarction. Reperfused infarction in the right liver lobe was surgically induced in six rats. Serial T1-weighted MRI was performed before and after intravenous injection of MP-2269 at 0.05 mmol/kg and repeated in the same rats 24 hours later after intravenous injection of gadophrin-2 at the same dosage (0.05 mmol/kg). The MR images were matched with corresponding histomorphological findings. The signal intensity and contrast ratio of infarcted and normal hepatic lobes were quantified and compared between the two agents during the postcontrast course. Before contrast, the infarcted lobe was indiscernible from normal liver on T1-weighted MRI. Shortly after injection of both MP-2269 and gadophrin-2, a negative contrast occurred between infarcted and normal liver because of a strong liver signal intensity enhancement and an inferior uptake in the necrotic liver. On delayed phase (>60 minutes), a necrosis-specific contrast enhancement (contrast ratio 1.6) developed with gadophrin-2 but not with MP-2269. The MR images matched well with corresponding histomorphological findings. Although both MP-2269 and gadophrin-2 feature an albumin-binding capacity, only gadophrin-2 displayed a persistent necrosis-specific contrast enhancement in the rat model of reperfused liver infarction. Therefore, the role of albumin binding in the mechanisms of NACAs should be reevaluated.