Central nervous system: review of clinical use of contrast media

Brain SPECT and perfusion MRI: do they provide complementary information about the tumour lesion and its grading?

AIM

To evaluate the relative and combined utility of ^99mTc-tetrofosmin (^99mTc-TF) brain single-photon-emission computed tomography (SPECT) and dynamic susceptibility contrast (DSC) perfusion magnetic resonance imaging (MRI) in grading brain gliomas.

MATERIALS AND METHODS

Thirty-six patients with clinically suspected brain tumours were assessed by ^99mTc-TF SPECT and DSC-MRI. Brain tumour malignancy was confirmed in all patients at histopathology. On both techniques brain lesions were evaluated via visual and semi-quantitative analysis methods (deriving tetrofosmin index [T-index] and relative cerebral blood volume [rCBV] ratios, respectively).

RESULTS

^99mTc-TF SPECT showed abnormally elevated tracer uptake in 31/36 patients whereas MRI detected the brain tumour in all patients. Optimal cut-off values of each index for discriminating between low- and high-grade gliomas were obtained through receiver operating characteristic (ROC) analyses. A T-index cut-off of 6.35 ensured 82% sensitivity and 71% specificity for discriminating between high- and low-grade gliomas, whereas a relative rCBV ratio cut-off of 1.80 achieved 91% sensitivity and 100% specificity. Requiring a positive result on either technique to characterise a high-grade glioma was associated with similar specificity and slightly increased sensitivity.

CONCLUSION

Both imaging techniques, ^99mTF SPECT and DSC MRI, may provide complementary indices of tumour grade and have an independent diagnostic value for high-risk tumours.

Drug Delivery Nanosystems for the Localized Treatment of Glioblastoma Multiforme

Glioblastoma multiforme is one of the most prevalent and malignant forms of central nervous system tumors. The treatment of glioblastoma remains a great challenge due to its location in the intracranial space and the presence of the blood⁻brain tumor barrier. There is an urgent need to develop novel therapy approaches for this tumor, to improve the clinical outcomes, and to reduce the rate of recurrence and adverse effects associated with present options. The formulation of therapeutic agents in nanostructures is one of the most promising approaches to treat glioblastoma due to the increased availability at the target site, and the possibility to co-deliver a range of drugs and diagnostic agents. Moreover, the local administration of nanostructures presents significant additional advantages, since it overcomes blood⁻brain barrier penetration issues to reach higher concentrations of therapeutic agents in the tumor area with minimal side effects. In this paper, we aim to review the attempts to develop nanostructures as local drug delivery systems able to deliver multiple agents for both therapeutic and diagnostic functions for the management of glioblastoma.

Diagnostic performance between contrast enhancement, proton MR spectroscopy, and amide proton transfer imaging in patients with brain tumors

PURPOSE

To explore the relationship among parameters of magnetic resonance spectroscopy (MRS) and amide proton transfer (APT) imaging, and to assess the diagnostic performance of MRS and APT imaging for grading brain tumors in comparison with contrast enhancement of conventional MRI for preoperative grading in patients with brain tumor.

MATERIALS AND METHODS

Institutional Review Board approval and written informed consent were obtained. Forty-one patients with suspected brain tumors were enrolled in the study. Single-voxel MRS and 2D APT imaging of the same slice level were conducted using a 3T MRI scanner. Positive or negative contrast enhancement on T₁ -weighted images was assessed by two neuroradiologists. Correlations among metabolite concentrations, metabolite ratios, and calculated histogram parameters, including mean APT (APT_mean ) and the 90th percentile of APT (APT₉₀ ) were assessed using Spearman's correlation coefficient. Diagnostic performance was evaluated with receiver operating characteristic (ROC) curve analysis for contrast enhancement and MRS and APT imaging. Values of P < 0.05 were considered statistically significant.

RESULTS

Positive correlations with statistical significance were found between total concentration of choline (Cho) and APT₉₀ (r = 0.49), and between Cho/creatine (Cr) and APT_mean (r = 0.65) as well as APT₉₀ (r = 0.49). A negative correlation with statistical significance was observed between NAA/Cr and APT_mean (r = -0.52). According to ROC curves, Cho/Cr, APT_mean , APT₉₀ , demonstrated higher area under the curve (AUC) values than that of contrast enhancement in grading gliomas.

CONCLUSION

Significant correlations were observed between metabolite concentrations and ratios on MRS and APT values. MRS and APT imaging showed comparable diagnostic capability for grading brain tumors, suggesting that both MRS and APT imaging offer potential for quantitatively assessing similar biological characteristics in brain tumors on noncontrast MRI.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:732-739.

A Japanese, Multicenter, Open-label, Phase 3 Study to Investigate the Safety and Efficacy of Gadobutrol for Contrast-enhanced MR Imaging of the Central Nervous System

PURPOSE

Gadobutrol 1.0 M is macrocyclic gadolinium-based contrast agent for magnetic resonance imaging (MRI). This multicenter, open-label, phase 3 study aimed to investigate the efficacy and safety of gadobutrol-enhanced versus unenhanced MRI in the visualization and diagnosis of central nervous system (CNS) lesions in Japanese patients.

METHODS

A total of 223 patients referred for contrast-enhanced MRI of the CNS underwent unenhanced and gadobutrol-enhanced (0.1 mmol/kg body weight) MRI. The unenhanced and combined (unenhanced and enhanced) images were evaluated by three independent readers in a blinded manner for degree of contrast enhancement, border delineation, internal morphology, and number of detected lesions (primary variables), and for primary diagnosis and diagnostic confidence. Final clinical diagnoses were established by an independent truth committee consisting of two neurosurgeons. Sensitivity, specificity, and accuracy were calculated for the detection of malignancy and the preciseness of diagnoses (secondary variables) by comparing the results obtained by the blinded readers and the truth committee.

RESULTS

Gadobutrol enhancement significantly improved three visualization parameters in MR images: contrast enhancement, border delineation, and internal morphology (P < 0.0001). Non-inferiority was achieved for mean number of lesions detected. Gadobutrol-enhanced imaging provided significant improvements in sensitivity and accuracy for the detection of malignant disease with no loss in specificity, and also improvements in accuracy of exact match diagnosis and diagnostic confidence. Drug-related adverse events were reported in 6 out of 223 patients (2.7%); all were non-serious.

CONCLUSION

Gadobutrol is an effective and well-tolerated contrast agent for MR imaging of the CNS.

Safety and Efficacy of Gadobutrol for Contrast-enhanced Magnetic Resonance Imaging of the Central Nervous System: Results from a Multicenter, Double-blind, Randomized, Comparator Study

PURPOSE

Contrast-enhanced magnetic resonance imaging (MRI) of the central nervous system (CNS) with gadolinium-based contrast agents (GBCAs) is standard of care for CNS imaging and diagnosis because of the visualization of lesions that cause blood–brain barrier breakdown. Gadobutrol is a macrocyclic GBCA with high concentration and high relaxivity. The objective of this study was to compare the safety and efficacy of gadobutrol 1.0 M vs unenhanced imaging and vs the approved macrocyclic agent gadoteridol 0.5 M at a dose of 0.1 mmol/kg bodyweight.

MATERIALS AND METHODS

Prospective, multicenter, double-blind, crossover trial in patients who underwent unenhanced MRI followed by enhanced imaging with gadobutrol or gadoteridol. Three blinded readers assessed the magnetic resonance images. The primary efficacy variables included number of lesions detected, degree of lesion contrast-enhancement, lesion border delineation, and lesion internal morphology.

RESULTS

Of the 402 treated patients, 390 patients received study drugs. Lesion contrast-enhancement, lesion border delineation, and lesion internal morphology were superior for combined unenhanced/gadobutrol-enhanced imaging vs unenhanced imaging (P < 0.0001 for all). Compared with gadoteridol, gadobutrol was non-inferior for all primary variables and superior for lesion contrast-enhancement, as well as sensitivity and accuracy for detection of malignant disease. The percentage of patients with at least one drug-related adverse event was similar for gadobutrol (10.0%) and gadoteridol (9.7%).

CONCLUSION

Gadobutrol is an effective and well-tolerated macrocyclic contrast agent for MRI of the CNS. Gadobutrol demonstrates greater contrast-enhancement and improved sensitivity and accuracy for detection of malignant disease than gadoteridol, likely because of its higher relaxivity.

Cerebral tumor or pseudotumor?

Pseudotumoral lesions are uncommon but important to identity lesions. They can occur during inflammatory diseases (systemic diseases, vasculitis, demyelinating diseases), infectious, and vascular diseases. Also, in a patient with a treated tumor, pseudo-progression and radionecrosis must be differentiated from the tumoral development. Diagnosis can be difficult on an MRI scan, but some MRI aspects in conventional sequences, diffusion, perfusion and spectroscopy can suggest the pseudotumoral origin of a lesion. Imaging must be interpreted according to the context, the clinic and the biology. The presence of associated intracranial lesions can orientate towards a systemic or infectious disease. A T2 hyposignal lesion suggests granulomatosis or histiocytosis, especially if a meningeal or hypothalamic-pituitary involvement is associated. Non-tumoral lesions are generally not hyperperfused. In the absence of a definitive diagnosis, the evolution of these lesions, whether under treatment or spontaneous, is fundamental.

Phase 3 efficacy and safety trial of gadobutrol, a 1.0 molar macrocyclic MR imaging contrast agent, in patients referred for contrast-enhanced MR imaging of the central nervous system

PURPOSE

Gadobutrol is a 1.0 M macrocyclic magnetic resonance imaging (MRI) contrast agent. A study was performed to evaluate the efficacy and safety of gadobutrol-enhanced versus unenhanced imaging for central nervous system (CNS) lesion visualization and detection.

MATERIALS AND METHODS

An international, multicenter, open-label, Phase III clinical trial. Patients underwent unenhanced and gadobutrol 1.0 M-enhanced (0.1 mmol/kg BW) MR imaging using a standardized protocol. Unenhanced and combined unenhanced/gadobutrol-enhanced images were scored by three independent, blinded readers for degree of lesion enhancement, border delineation, internal morphology, and total number of lesions detected (primary efficacy variables). Exact match of the MR diagnoses with the final clinical diagnosis, detection of malignant CNS lesions, and confidence in diagnosis were secondary efficacy variables.

RESULTS

Of 343 enrolled patients, 321 were evaluated for efficacy. All primary efficacy endpoints were met: superiority was demonstrated for gadobutrol-enhanced versus unenhanced MR images (P < 0.0001 in all cases) for lesion enhancement, border delineation, and internal morphology. Noninferiority was met for mean number of lesions detected. There were improvements in the sensitivity of malignant lesion detection, without a loss in specificity, exact-match diagnostic accuracy, and reader confidence. Treatment-related adverse events were reported in 4.1% (n = 14); all were nonserious.

CONCLUSION

Gadobutrol 1.0M is an effective and well-tolerated contrast agent for CNS MRI.

Contrast-enhanced magnetic resonance imaging in pediatric patients: review and recommendations for current practice

Magnetic resonance imaging (MRI), frequently with contrast enhancement, is the preferred imaging modality for many indications in children. Practice varies widely between centers, reflecting the rapid pace of change and the need for further research. Guide-line changes, for example on contrast-medium choice, require continued practice reappraisal. This article reviews recent developments in pediatric contrast-enhanced MRI and offers recommendations on current best practice. Nine leading pediatric radiologists from internationally recognized radiology centers convened at a consensus meeting in Bordeaux, France, to discuss applications of contrast-enhanced MRI across a range of indications in children. Review of the literature indicated that few published data provide guidance on best practice in pediatric MRI. Discussion among the experts concluded that MRI is preferred over ionizing-radiation modalities for many indications, with advantages in safety and efficacy. Awareness of age-specific adaptations in MRI technique can optimize image quality. Gadolinium-based contrast media are recommended for enhancing imaging quality. The choice of most appropriate contrast medium should be based on criteria of safety, tolerability, and efficacy, characterized in age-specific clinical trials and personal experience.

Contrast-enhanced MR imaging in neuroimaging

MR imaging without and with gadolinium-based contrast agents (GBCAs) is an important imaging tool for defining normal anatomy and characteristics of lesions. GBCAs have been used in contrast-enhanced MR imaging in defining and characterizing lesions of the central nervous system for more than 20 years. The combination of unenhanced and GBCA-enhanced MR imaging is the clinical gold standard for the noninvasive detection and delineation of most intracranial and spinal lesions. MR imaging has a high predictive value that rules out neoplasm and most inflammatory and demyelinating processes of the central nervous system.

MR imaging of neoplastic central nervous system lesions: review and recommendations for current practice

MR imaging is the preferred technique for the diagnosis, treatment planning, and monitoring of patients with neoplastic CNS lesions. Conventional MR imaging, with gadolinium-based contrast enhancement, is increasingly combined with advanced, functional MR imaging techniques to offer morphologic, metabolic, and physiologic information. This article provides updated recommendations to neuroradiologists, neuro-oncologists, neurosurgeons, and radiation oncologists on the practical applications of MR imaging of neoplastic CNS lesions in adults, with particular focus on gliomas, based on a review of the clinical trial evidence and personal experiences shared at a recent international meeting of experts in neuroradiology, neuro-oncology, neurosurgery, and radio-oncology.

Magnetic resonance evaluation of brain metastases from systemic malignances with two doses of gadobutrol 1.0 m compared with gadoteridol: a multicenter, phase ii/iii study in patients with known or suspected brain metastases

OBJECTIVES

To determine the efficacy and safety of 2 doses of gadobutrol 1.0 M (0.1 and 0.2 mmol/kg body weight [BW]), compared with gadoteridol 0.5 M (0.2 mmol/kg BW), in contrast-enhanced magnetic resonance imaging (CE-MRI) of brain metastases in patients with known or suspected brain metastases from systemic malignancies. The study also compared the usefulness of gadobutrol in treatment planning for stereotactic radiosurgery (SRS).

MATERIALS AND METHODS

This was a Phase II/III, multicenter, single-blind, randomized, controlled, crossover, intraindividual comparison study. Each patient underwent one MRI study examination with gadobutrol and the other with gadoteridol, each at a dose of 0.1 mmol/kg BW, administered twice, for a total dose of 0.2 mmol/kg BW. Image acquisition was carried out after the first and second doses of gadobutrol, but only after the second dose of gadoteridol. Contrast agents were assigned in a randomized order and their administration separated by an interval of 1 to 14 days. Images were evaluated through blinded readings by 3 independent experienced radiologists. Treatment planning for SRS was assessed in a blinded manner, as a consensus between a diagnostic neuroradiologist and a radiation oncologist, in addition to the clinical investigator's assessment. The safety and tolerability of gadobutrol and gadoteridol were evaluated in all patients who received the study drugs. The primary efficacy variable was the number of lesions detected in CE-MRI images; the secondary efficacy variables were the degree of contrast enhancement and border delineation of lesions, and experts' confidence in treatment planning for SRS.

RESULTS

A total of 175 patients were enrolled and randomized, with 164 (93.7%) included in the safety analysis set, and 151 (86.2%) evaluable in the efficacy analysis. The mean number of detected lesions per patient using the average of the 3 blinded readers was 6.28, 6.92, and 6.87 for gadobutrol 0.1 and 0.2 mmol/kg BW, and gadoteridol 0.2 mmol/kg BW, respectively. Noninferiority of gadobutrol (both doses) to gadoteridol 0.2 mmol/kg BW was demonstrated. The degree of contrast enhancement and the border delineation of each lesion were categorized as "good" or "excellent" for most lesions for both agents. Almost all enhanced images were rated as "confident" in treatment planning for SRS. Sixty-five (43%) and 62 (41%) patients in the gadobutrol 0.1 and 0.2 mmol/kg BW groups, respectively, were selected as eligible for SRS treatment. The percentage of images assessed as "gadobutrol was better than gadoteridol" was higher than that assessed as "gadoteridol was better than gadobutrol" for both doses of gadobutrol. Eight adverse events were reported as being related to the study drug in 7 patients (4.3%) in each group.

CONCLUSION

In this study, a single dose of gadobutrol was shown to be noninferior to a double dose of gadoteridol at detecting brain metastases, and could be effectively used for treatment planning in patients eligible for SRS. A dose of gadobutrol 0.1 mmol/kg BW is recommended as the clinical dose for the detection of brain metastases.

Hexylether derivative of pyropheophorbide-a (HPPH) on conjugating with 3gadolinium(III) aminobenzyldiethylenetriaminepentaacetic acid shows potential for in vivo tumor imaging (MR, Fluorescence) and photodynamic therapy

Conjugates of 3-(1'-hexyloxyethyl)-3-devinyl pyropheophorbide-a (HPPH) with multiple Gd(III)aminobenzyl diethylenetriamine pentacetic acid (ADTPA) moieties were evaluated for tumor imaging and photodynamic therapy (PDT). In vivo studies performed in both mice and rat tumor models resulted in a significant MR signal enhancement of tumors relative to surrounding tissues at 24 h postinjection. The water-soluble (pH: 7.4) HPPH-3Gd(III) ADTPA conjugate demonstrated high potential for tumor imaging by MR and fluorescence. This agent also produced long-term tumor cures via PDT. An in vivo biodistribution study with the corresponding (14)C-analogue also showed significant tumor uptake 24 h postinjection. Toxicological evaluations of HPHH-3Gd(III)ADTPA administered at and above imaging/therapeutic doses did not show any evidence of organ toxicity. Our present study illustrates a novel approach for the development of water-soluble "multifunctional agents", demonstrating efficacy for tumor imaging (MR and fluorescence) and phototherapy.

Brain tumor enhancement in magnetic resonance imaging at 3 tesla: intraindividual comparison of two high relaxivity macromolecular contrast media with a standard extracellular gd-chelate in a rat brain tumor model

OBJECTIVES

The aim of this study was to evaluate lesion enhancement (LE) and contrast-to-noise ratio (CNR) properties of P846, a new intermediate sized, high relaxivity Gd-based contrast agent at 3 Tesla in a rat brain glioma model, and to compare this contrast agent with a high relaxivity, macromolecular compound (P792), and a standard extracellular Gd-chelate (Gd-DOTA).

MATERIALS AND METHODS

Seven rats with experimental induced brain glioma were evaluated using 3 different contrast agents, with each MR examination separated by at least 24 hours. The time between injections assured sufficient clearance of the agent from the tumor, before the next examination. P792 (Gadomelitol, Guerbet, France) and P846 (a new compound from Guerbet Research) are macromolecular and high relaxivity contrast agents with no protein binding, and were compared with the extracellular agent Gd-DOTA (Dotarem, Guerbet, France). T1w gradient echo sequences (TR/TE 200 milliseconds/7.38 milliseconds, flip angle = 90 degrees , acquisition time: 1:42 minutes:sec, voxel size: 0.2 x 0.2 x 2.0 mm, FOV = 40 mm, acquisition matrix: 256 x 256) were acquired before and at 5 consecutive time points after each intravenous contrast injection in the identical slice orientation, using a dedicated 4-channel head array animal coil. The order of contrast media injection was randomized, with however Gd-DOTA used either as the first or second contrast agent. Contrast agent dose was adjusted to compensate for the different T1 relaxivities of the 3 agents. Signal-to-noise ratio, CNR, and LE were evaluated using region-of-interest analysis. A veterinary histopathologist confirmed the presence of a glioma in each subject, after completion of the imaging study.

RESULTS

P792 showed significantly less LE as compared with Gd-DOTA within the first 7 minutes after contrast agent injection (P < 0.05) with, however, reaching comparable LE values at 9 minutes after injection (P = 0.07). However, P792 provided significantly less CNR as compared with Gd-DOTA (P < 0.05) for all examination time points. P846 provided comparable but persistent LE as compared with Gd-DOTA (P < 0.05) and demonstrated significantly greater LE and CNR when compared with P792 (P < 0.05). No statistically significant differences between CNR values for Gd-DOTA and P846 were noted for all examination time points (P < 0.05), with P846 administered at one-fourth the dose as compared with Gd-DOTA.

CONCLUSION

The intravascular contrast medium P792 showed significantly less LE and CNR in comparison to Gd-DOTA and P846, suggesting that it does not show marked extravasation from tumor neocapillaries and does not significantly cross the disrupted blood brain-barrier in this rat glioma model. In distinction, P846 provides comparable enhancement properties at a field strength of 3 Tesla to the extracellular contrast agent Gd-DOTA, using the adjusted dose, suggesting that it crosses the disrupted blood-brain-barrier and tumor capillaries, most likely based on the decreased molecular weight as compared with P792. At the same time, the high relaxivity of this compound allows for decreasing the injected gadolinium dose by a factor of 4 whereas providing comparable enhancement properties when compared with a standard extracellular Gd-chelate (Gd-DOTA) at a dose of 0.1 mmol/kg body weight.

Improving lesion detection and visualization: implications for neurosurgical planning and follow-up

Contrast-enhanced magnetic resonance (MR) imaging is considered the most sensitive method for detecting tumors in the central nervous system (CNS). The primary objective is to improve lesion detection, delineation, and characterization (benign or malignant) in order to more accurately define the location, extent, and type of disease and the appropriate treatment option for improved patient outcome (surgical intervention, radiation therapy or cytotoxic chemotherapy). This article reviews the various types of tumor occurring in the brain and the specific role of contrast-enhanced MR imaging for the evaluation of these tumors. Emphasis is placed on the value of contrast-enhanced MR imaging in the evaluation of primary intra-axial brain lesions and how high relaxivity contrast agents such as MultiHance (Bracco Imaging, Milan, Italy) might improve detection, treatment planning, and follow-up.

Brain Tumor Enhancement in MR Imaging at 3 Tesla

PURPOSE

The purpose of this study was to compare brain and tumor signal characteristics of T1-weighted turbo spin-echo (TSE) and gradient recalled echo (GRE) sequence techniques at 3 T compared to TSE at 1.5 T, focusing on the detection of contrast enhancement, in a standardized animal model of a brain glioma.

MATERIALS AND METHODS

Twelve rats with implanted brain gliomas were evaluated at 1.5 and 3 T using matched hardware configurations. At 1.5 T, scanning was performed using a TSE sequence optimized for field strength (480/15 milliseconds; 125 Hz/Px) with postcontrast scans acquired at multiple time points after gadoteridol injection (0.1 mmol/kg). At 3 T, scanning was performed using the 1.5 T equivalent TSE as well as with TSE and GRE techniques optimized for 3 T. Signal-to-noise ratio (SNR) of brain and tumor and tumor contrast-to-noise ratio (CNR) were evaluated for all techniques at both field strengths.

RESULTS

Postcontrast tumor SNR (63.7 +/- 10.8 vs. 29.5 +/- 4.3; P < 0.0001) and brain SNR (35.8 +/- 1.5 vs. 19.1 +/- 0.7; P < 0.0001) showed significant increase at 3 T using matched TSE. Comparing TSE optimized to each field strength (for optimized gray-white contrast), tumor and brain SNR still showed a significant increase at 3 T of 73% and 56%, respectively (both P < 0.0001). Comparing TSE at 1.5 T and GRE at 3 T, tumor SNR increased by 105%, whereas brain SNR increased by 141% (both P < 0.0001). Tumor CNR with matched TSE increased by 168% (P < 0.0001), with optimized TSE by 111% (P < 0.0001), and with GRE at 3 T versus TSE at 1.5 T by 36% (P < 0.001). With additional adjustments for echo time the gain in tumor CNR for 2D GRE may again reach 60%.

CONCLUSIONS

With TSE at 3 T, the SNR gain comes close to the theoretically expected doubling with an even higher tumor CNR increase. In a clinical like setting at 3 T, where a T1w GRE sequence is used, tumor CNR gain is limited. Contrast dose should therefore not be decreased at 3 T.

Intraaxial brain masses: MR imaging-based diagnostic strategy--initial experience

PURPOSE

To develop and retrospectively determine the accuracy of a magnetic resonance (MR) imaging strategy to differentiate intraaxial brain masses, with histologic findings or clinical diagnosis as the reference standard.

MATERIALS AND METHODS

The study was HIPAA compliant and was approved by the institutional review board. A waiver of informed consent was obtained. A strategy was developed on the basis of conventional MR imaging, diffusion-weighted MR imaging, perfusion MR imaging, and proton MR spectroscopy to classify intraaxial masses as low-grade primary neoplasms, high-grade primary neoplasms, metastatic neoplasms, abscesses, lymphomas, tumefactive demyelinating lesions (TDLs), or encephalitis. The strategy was evaluated by using data from 111 patients (46 women, 65 men; mean age, 48.9 years) with imaging results available on a departmental picture archiving and communication system from a 5-year search period. Bayesian statistics of the strategy elements and three clinical tasks were calculated.

RESULTS

Search results identified 44 patients with high-grade and 14 with low-grade primary neoplasms, 24 with abscesses, 12 with lymphoma, 11 with TDLs, five with metastases, and one with encephalitis who had undergone conventional and advanced MR imaging. However, only 40 patients (25 women, 15 men; mean age, 45 years) had undergone all studies and had data to allow completion of the entire strategy. Accuracy, sensitivity, and specificity of the strategy, respectively, were 90%, 97%, and 67% for discrimination of neoplastic from nonneoplastic diseases, 90%, 88%, and 100% for discrimination of high-grade from low-grade neoplasms, and 85%, 84%, and 87% for discrimination of high-grade neoplasms and lymphoma from low-grade neoplasms and nonneoplastic diseases.

CONCLUSION

An integrated MR imaging-based strategy, which is accurate in differentiation of several intraaxial brain masses, was proposed.

Part I: Spinal-cord neoplasms—intradural neoplasms

Intradural spinal-cord tumours are an uncommon but important consideration in the differential diagnosis of patients with back pain, radicular pain, sensorimotor deficits, or sphincter dysfunction. Intradural spinal tumours can be divided into intramedullary and extramedullary spinal-cord tumours on the basis of their anatomical relation to the spinal parenchyma. The heterogeneous cell composition of the intradural compartment allows the formation of neoplasms, arising from glial cells, neurons, and cells of spinal vasculature. Additionally, developmental tumours, metastases, and intradural extension of extradural tumours are represented. In this Review, we discuss the published work on intradural spinal-cord tumours in terms of epidemiological, radiographic, and histological characteristics. Surgical and adjuvant treatment strategies are also reviewed.

Advanced MR Imaging Techniques in the Diagnosis of Intraaxial Brain Tumors in Adults

Intraaxial brain masses are a significant health problem and present several imaging challenges. The role of imaging is no longer limited to merely providing anatomic details. Sophisticated magnetic resonance (MR) imaging techniques allow insight into such processes as the freedom of water molecule movement, the microvascular integrity and hemodynamic characteristics, and the chemical makeup of certain compounds of masses. The role of the most commonly used advanced MR imaging techniques-perfusion imaging, diffusion-weighted imaging, and MR spectroscopy-in the diagnosis and classification of the most common intraaxial brain tumors in adults is explored. These lesions include primary neoplasms (high- and low-grade), secondary (meta-static) neoplasms, lymphoma, tumefactive demyelinating lesions, abscesses, and encephalitis. Application of a diagnostic algorithm that integrates advanced MR imaging features with conventional MR imaging findings may help the practicing radiologist make a more specific diagnosis for an intraaxial tumor.

Low-density lipoprotein nanoparticles as magnetic resonance imaging contrast agents

Low-density lipoproteins (LDLs) are a naturally occurring endogenous nanoplatform in mammalian systems. These nanoparticles (22 nm) specifically transport cholesterol to cells expressing the LDL receptor (LDLR). Several tumors overexpress LDLRs presumably to provide cholesterol to sustain a high rate of membrane synthesis. Amphiphilic gadolinium (Gd)-diethylenetriaminepentaacetic acid chelates have been incorporated into the LDL to produce a novel LDLR-targeted magnetic resonance imaging (MRI) contrast agent. The number of Gd chelates per LDL particle ranged between 150 and 496 Gd(III). In vitro studies demonstrated that Gd-labeled LDL retained a similar diameter and surface charge as the native LDL particle. In addition, Gd-labeled LDL retained selective cellular binding and uptake through LDLR-mediated endocytosis. Finally, Gd-labeled LDLs exhibited significant contrast enhancement 24 hours after administration in nude mice with human hepatoblastoma G2 xenografts. Thus, Gd-labeled LDL demonstrates potential use as a targeted MRI contrast agent for in vivo tumor detection.

Contrast Enhancement of Central Nervous System Lesions: Multicenter Intraindividual Crossover Comparative Study of Two MR Contrast Agents

PURPOSE

To prospectively compare gadobenate dimeglumine with gadopentetate dimeglumine (0.1 mmol per kilogram body weight) for enhanced magnetic resonance (MR) imaging of central nervous system (CNS) lesions.

MATERIALS AND METHODS

This study was HIPAA-compliant at U.S. centers and was conducted at all centers according to the Good Clinical Practice standard. Institutional review board and regulatory approval were granted; written informed consent was obtained. Seventy-nine men and 78 women (mean age, 50.5 years +/- 14.4 [standard deviation]) were randomized to group A (n = 78) or B (n = 79). Patients underwent two temporally separated 1.5-T MR imaging examinations. In randomized order, gadobenate followed by gadopentetate was administered in group A; order of administration was reversed in group B. Contrast agent administration (volume, speed of injection), imaging parameters before and after injection, and time between injections and postinjection acquisitions were identical for both examinations. Three blinded neuroradiologists evaluated images by using objective image interpretation criteria for diagnostic information end points (lesion border delineation, definition of disease extent, visualization of internal morphologic features of the lesion, enhancement of the lesion) and quantitative parameters (percentage of lesion enhancement, contrast-to-noise ratio [CNR]). Overall diagnostic preference in terms of lesion conspicuity, detectability, and diagnostic confidence was assessed. Between-group comparisons were performed with Wilcoxon signed rank test.

RESULTS

Readers 1, 2, and 3 demonstrated overall preference for gadobenate in 75, 89, and 103 patients, compared with that for gadopentetate in seven, 10, and six patients, respectively (P < .0001). Significant (P < .0001) preference for gadobenate was demonstrated for diagnostic information end points, percentage of lesion enhancement, and CNR. Superiority of gadobenate was significant (P < .001) in patients with intraaxial and extraaxial lesions.

CONCLUSION

Gadobenate compared with gadopentetate at an equivalent dose provides significantly better enhancement and diagnostic information for CNS MR imaging.

The Efficacy of Gadobenate Dimeglumine (Gd-BOPTA) at 3 Tesla in Brain Magnetic Resonance Imaging

OBJECTIVES

The objectives of this study were to analyze the differences in contrast enhancement using gadobenate dimeglumine (Gd-BOPTA or MultiHance) at 3 T versus 1.5 T and to compare Gd-BOPTA with a standard gadolinium chelate, gadopentetate dimeglumine (Gd-DTPA or Magnevist), at 3 T in a rat glioma model.

MATERIALS AND METHODS

Twelve rats with surgically implanted gliomas were randomized to either comparing Gd-BOPTA at 1.5 T versus 3 T (n=7) or comparing Gd-BOPTA and Gd-DTPA at 3 T (n=5). Matched T1-weighted spin-echo techniques were used for both comparisons and the order of examinations was randomized. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and lesion enhancement (LE) were evaluated using a region-of-interest analysis. A veterinary histopathologist evaluated all brain specimens.

RESULTS

In the evaluation of Gd-BOPTA at 3 T and 1.5 T, there were significant increases in SNR, LE, and CNR at 3 T. Average increases in brain and tumor SNR were 93% (P<0.0001) and 92% (P<0.0001), respectively. CNR increased by 121% (P<0.0001). Comparison of Gd-BOPTA and Gd-DTPA at 3 T demonstrated significantly higher CNR and LE with Gd-BOPTA. CNR increased by 35% (P=0.002). LE increased by 44% (P=0.03).

CONCLUSIONS

Gd-BOPTA provides significantly higher CNR at 3 T compared with 1.5 T and also demonstrates significantly higher CNR when compared with a standard Gd-chelate at 3 T. As a result of transient protein binding, Gd-BOPTA may be superior to standard gadolinium chelates in neurologic imaging at 3 T.

T1-Weighted Imaging of the Brain at 3 Tesla Using a 2-Dimensional Spoiled Gradient Echo Technique

RATIONALE AND OBJECTIVES

The objective of this study was to evaluate a 2-dimensional spoiled gradient echo (GRE) imaging approach using a very short in-phase TE for routine T1-weighted imaging of the brain at 3 T.

MATERIALS AND METHODS

Patient examinations were compared from a 3 T magnetic resonance (MR) unit located immediately adjacent to a similarly equipped 1.5 T unit. Pre- and postcontrast T1-weighted images were evaluated and compared at 1.5 versus 3 T with a 2-dimensional (2-D) spin echo sequence used at 1.5 T and a 2-D GRE sequence at 3 T. The 2 MR systems used are from the same vendor, use similar 8-channel coils, and use identical gradients. The T1-weighted GRE sequence, used at 3 T, relies on a short TE (2.4 ms) to limit flow-related and susceptibility artifacts. Region-of-interest analysis was performed on 16 different sagittal patient examinations at both field strengths (32 total) and similarly on 10 different pre- and postcontrast axial examinations (40 total). Four blinded neuroradiologists also evaluated these studies.

RESULTS

Using an off-midline sagittal slice depicting the caudate nucleus (signal-to-noise ratio [SNR] 163 +/- 28 vs. 70 +/- 7, 3 T vs. 1.5 T) and corona radiata (SNR 214 +/- 35 vs. 82 +/- 10), 3 T markedly outperformed 1.5 T in both SNR and contrast-to-noise ratio (CNR) (51 +/- 14 vs. 12 +/- 5). On axial imaging, despite a reduction in slice thickness (5 to 3 mm) and scan time (5 to 1 minute), there was no significant difference pre- or postcontrast in SNR and CNR comparing 3 and 1.5 T. On blinded film review, 3 T performed slightly better on sagittal scans than 1.5 T in regard to motion artifacts (reduced), gray-white matter differentiation, and overall image quality. On axial scans, 3 T performed markedly better in all 3 categories both pre- and postcontrast. In regard to overall image quality, 3 T was preferred 9:2 precontrast and 4:1 postcontrast.

CONCLUSIONS

High-quality, thin-section (3-mm) T1-weighted imaging can be readily performed at 3 T using a short TE 2-D GRE technique. This approach offers superior SNR and CNR with reduced motion artifacts and scan time as compared with imaging at 1.5 T and is advocated for routine brain imaging at 3 T. It is robust (used in over 1500 patients to date) and does not experience significant specific absorption ratio limitations, poor tissue contrast, or accentuated motion artifacts like encountered with spin echo T1-weighted imaging at 3 T.