Toxicity of MRI and CT contrast agents

Poly(para-phenylene ethynylene)s functionalized with Gd(III) chelates as potential MRI contrast agents

A poly(para-phenylene ethynylene) with water-solubilizing groups and Gd(III) chelates conjugated to the polymer backbone was designed and synthesized. Pre- and post-polymerization functionalization approaches were explored and the pre-polymerization approach for the introduction of the Gd(III) chelate was found to be more successful. The UV–vis absorption and fluorescence emission properties of the protected polymers were characterized and were found to be consistent with the results expected for this class of polymers. Removal of the protecting groups followed by chelation of Gd(III) led to a water-dispersible polymer. Relaxivity measurements were performed on this polymer with the aim of evaluating its potential as a new MRI contrast agent, and an r1 of 1.37 L mmol–1 s–1 at 310 K and 20 MHz was determined. These results, along with dynamic light scattering analyses, suggested that the polymers formed micrometre-sized assemblies in aqueous solution. Although the relaxivity was relatively modest, these results provide important insights into the assembly properties of this new class of polymers and into the design criteria for future agents.

Adaptive radiotherapy based on contrast enhanced cone beam CT imaging

Cone beam CT (CBCT) imaging has become an integral part of radiation therapy, with images typically used for offline or online patient setup corrections based on bony anatomy co-registration. Ideally, the co-registration should be based on tumor localization. However, soft tissue contrast in CBCT images may be limited. In the present work, contrast enhanced CBCT (CECBCT) images were used for tumor visualization and treatment adaptation. Material and methods. A spontaneous canine maxillary tumor was subjected to repeated cone beam CT imaging during fractionated radiotherapy (10 fractions in total). At five of the treatment fractions, CECBCT images, employing an iodinated contrast agent, were acquired, as well as pre-contrast CBCT images. The tumor was clearly visible in post-contrast minus pre-contrast subtraction images, and these contrast images were used to delineate gross tumor volumes. IMRT dose plans were subsequently generated. Four different strategies were explored: 1) fully adapted planning based on each CECBCT image series, 2) planning based on images acquired at the first treatment fraction and patient repositioning following bony anatomy co-registration, 3) as for 2), but with patient repositioning based on co-registering contrast images, and 4) a strategy with no patient repositioning or treatment adaptation. The equivalent uniform dose (EUD) and tumor control probability (TCP) calculations to estimate treatment outcome for each strategy. Results. Similar translation vectors were found when bony anatomy and contrast enhancement co-registration were compared. Strategy 1 gave EUDs closest to the prescription dose and the highest TCP. Strategies 2 and 3 gave EUDs and TCPs close to that of strategy 1, with strategy 3 being slightly better than strategy 2. Even greater benefits from strategies 1 and 3 are expected with increasing tumor movement or deformation during treatment. The non-adaptive strategy 4 was clearly inferior to all three adaptive strategies. Conclusion. CECBCT may prove useful for adaptive radiotherapy.

Stage of chronic kidney disease is an outcome-predicting factor of angioplasty for atheromatous renal artery stenosis

Angioplasty with insertion of an endoprosthesis is an effective treatment for atheromatous renal artery stenosis (ARAS). However, this procedure may cause deterioration in renal function, and it is imperative to define the cases that could benefit from angioplasty. From 456 suspected renovascular hypertension cases, 33 were given a diagnosis of unilateral ARAS on renal arteriography. These unilateral ARAS cases were treated by angioplasty, and their baseline variables were evaluated with respect to the improvement achieved in post-angioplastic renal function of the treated side as measured by renal scintigram. The estimated glomerular filtration rate (eGFR) was the only variable that was significantly different between cases that showed improvement in renal function and those that did not. Cases that showed improvement in renal function had lower pre-angioplasty eGFR compared with cases that did not show improvement (59±24 ml min⁻¹ 1.73 m⁻² vs. 76±12 ml min⁻¹ 1.73 m⁻², P=0.04), and cases showing improvement were generally at later stages of chronic kidney disease (CKD). Most patients without improvement, who were generally at earlier stages of CKD, had a systemic blood pressure reduction after angioplasty. The present findings indicate that the baseline CKD stage could be used to predict the outcome of angioplasty for ARAS.

First experience using intraoperative contrast-enhanced ultrasound during endovascular aneurysm repair for infrarenal aortic aneurysms

BACKGROUND

Endovascular aortic repair (EVAR) has become an additional treatment option for patients with infrarenal aortic aneurysms and suitable aortic morphology. However, endoleaks are commonly encountered and represent a relevant risk for secondary treatment failure. In addition, impaired renal function or allergic reactions to intravascular iodine application might represent exclusion criteria for conventional infrarenal endovascular aortic repair using intraoperative angiography with iodine contrast media. Real-time contrast-enhanced ultrasound (CEUS) with a low mechanical index (MI) is a promising method recently introduced for follow up after endovascular infrarenal aortic repair.

METHODS

In this study, intraoperative CEUS using SonoVue as ultrasound contrast agent was evaluated in 17 patients for localization of the proximal infrarenal landing zone, the distal iliac fixation area, and identification of endoleaks in patients suitable for endovascular aortic repair with an infrarenal aortic neck > or =10 mm and non-aneurysmal common iliac arteries. For comparison, 20 patients were treated by conventional EVAR using intraoperative fluoroscopy and iodine contrast media.

RESULTS

Intraoperative application of contrast-enhanced ultrasound (iCEUS) for identification of the infrarenal landing zone and proximal stent graft release was achieved in 14 out of 17 patients (82.4%), as verified by intraoperative angiography or postinterventional imaging. Intraoperative CEUS-assisted visualization of the distal fixation area proximal to the level of the iliac bifurcation was achieved in 89.3% (25 out of 28 iliac arteries examined) in comparison to intraoperative angiography or postinterventional CEUS, computed tomography (CT), or magnetic resonance (MR) angiography. Three selected patients having contraindications for iodine-based contrast media were treated by iCEUS-assisted EVAR without the use of any iodine contrast during fluoroscopy. Time for exposure to intraoperative radiation, volume of contrast medium used, and the number of intraoperative angiographies and postinterventional CT or MR angiographies were significantly reduced in the iCEUS-assisted EVAR group in comparison to conventional endovascular aortic treatment (P < .002 or less for all parameters). Intraoperative application of CEUS detected more endoleaks than conventional EVAR (8/17 vs 4/20; P = .08) treated by proximal stent graft extension in one symptomatic patient with a type Ia endoleak.

CONCLUSIONS

Intraoperative CEUS-assisted EVAR in patients with infrarenal aortic aneurysms represents a new option for intraoperative visualization of aortoiliac segments required as proximal or distal fixation zones and identification of endoleaks, especially in those patients with contraindications for usage of iodine-containing contrast agents, in association with a reduction of iodine contrast media used and radiation exposure during fluoroscopy.

Magnetic resonance imaging of multifunctional pluronic stabilized iron-oxide nanoparticles in tumor-bearing mice

We are investigating the magnetic resonance imaging characteristics of magnetic nanoparticles (MNPs) that consist of an iron-oxide magnetic core coated with oleic acid (OA), then stabilized with a pluronic or tetronic block copolymer. Since pluronics and tetronics vary structurally, and also in the ratio of hydrophobic (poly[propylene oxide]) and hydrophilic (poly[ethylene oxide]) segments in the polymer chain and in molecular weight, it was hypothesized that their anchoring to the OA coating around the magnetic core could significantly influence the physical properties of MNPs, their interactions with biological environment following intravenous administration, and ability to localize to tumors. The amount of block copolymer associated with MNPs was seen to depend upon their molecular structures and influence the characteristics of MNPs. Pluronic F127-modified MNPs demonstrated sustained and enhanced contrast in the whole tumor, whereas that of Feridex IV was transient and confined to the tumor periphery. In conclusion, our pluronic F127-coated MNPs, which can also be loaded with anticancer agents for drug delivery, can be developed as an effective cancer theranostic agent, i.e. an agent with combined drug delivery and imaging properties.