Intraindividual Comparison of Gadobenate Dimeglumine and Gadobutrol for Cerebral Magnetic Resonance Perfusion Imaging at 1.5 T

MRA of the Supraaortic Vasculature: Comparison of Gadobutrol and Gadoterate Meglumine at 1.5 T

BACKGROUND

Gadobutrol (GB) and gadoterate meglumine (GM) are contrast agents used for contrast-enhanced magnetic resonance angiography (CEMRA). Supraaortic vasculature (SAV) CEMRAs are used to evaluate stroke risk and neurologic symptoms. There is a need to compare the SAV CEMRA image quality obtained with GB and GM.

PURPOSE

To intra-individually compare MRA images obtained with equimolar GB and GM at 1.5 T in the SAV.

STUDY TYPE

Prospective, crossover.

POPULATION

Twenty-eight subjects (54 ± 13 years; 17 female).

FIELD STRENGTH/SEQUENCE

1.5 T; three-dimensional (3D) gradient recalled echo.

ASSESSMENT

Quantitative image quality was measured by normalized signal intensity (SI_n ) [SI_n  = SI blood/SD blood] and contrast ratio (CR) [CR = SI blood/SI muscle], determined by an observer (JWC) with 1 year of vascular imaging experience. Three radiologists (AS, PA, and MU) with (5, 5, and 6 years of) vascular imaging experience evaluated image quality by Likert-scale ratings (of image impression, wall conspicuity, and artifact absence).

STATISTICAL TESTS

SI_n and CR were compared with paired t-tests or Wilcoxon signed-rank tests and Bland-Altman plots. Qualitative ratings were compared with Wilcoxon signed-rank test.

RESULTS

No significant difference in SI_n was found between GB and GM. CRs with GB were significantly higher than GM at the right common carotid (6.9 ± 2.5 vs. 4.8 ± 1), left internal carotid (7.3 ± 2 vs. 4.4 ± 1.2), right internal carotid (7.7 ± 2.2 vs. 5 ± 1.1), and left vertebral (6.6 ± 2.2 vs. 4.5 ± 1.1) arteries. Bland-Altman plots showed relatively greater differences between GB and GM at higher CRs and SI_n s. GM showed significantly higher artifact than GB (3.56 ± 0.52 vs. 3.36 ± 0.46) and significantly lower overall image quality (10.73 ± 1.45 vs. 11.26 ± 1.58) at the left vertebral artery.

DATA CONCLUSION

At 1.5 T and equimolar demonstration, GB (0.1 mL/kg, i.e., 0.1 mmol/kg) showed higher CRs in the SAV compared to GM (0.2 mL/kg, i.e., 0.1 mmol/kg) at most vessels. Subjective image quality was not significantly different between the two agents for most vessels.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 2.

Asymptomatic carotid artery stenosis is associated with cerebral hypoperfusion

OBJECTIVE

We have shown that almost 50% of patients with asymptomatic carotid stenosis (ACS) will demonstrate cognitive impairment. Recent evidence has suggested that cerebral hypoperfusion is an important cause of cognitive impairment. Carotid stenosis can restrict blood flow to the brain, with consequent cerebral hypoperfusion. In contrast, cross-hemispheric collateral compensation through the Circle of Willis, and cerebrovascular vasodilation can also mitigate the effects of flow restriction. It is, therefore, critical to develop a clinically relevant measure of net brain perfusion in patients with ACS that could help in risk stratification and in determining the appropriate treatment. To determine whether ACS results in cerebral hypoperfusion, we developed a novel approach to quantify interhemispheric cerebral perfusion differences, measured as the time to peak (TTP) and mean transit time (MTT) delays using perfusion-weighted magnetic resonance imaging (PWI) of the whole brain. To evaluate the utility of using clinical duplex ultrasonography (DUS) to infer brain perfusion, we also assessed the relationship between the PWI findings and ultrasound-based peak systolic velocity (PSV).

METHODS

Structural and PWI of the brain and magnetic resonance angiography of the carotid arteries were performed in 20 patients with ≥70% ACS. DUS provided the PSV, and magnetic resonance angiography provided plaque geometric measures at the stenosis. Volumetric perfusion maps of the entire brain from PWI were analyzed to obtain the mean interhemispheric differences for the TTP and MTT delays. In addition, the proportion of brain volume that demonstrated a delay in TTP and MTT was also measured. These proportions were measured for increasing severity of perfusion delays (0.5, 1.0, and 2.0 seconds). Finally, perfusion asymmetries on PWI were correlated with the PSV and stenosis features on DUS using Pearson's correlation coefficients.

RESULTS

Of the 20 patients, 18 had unilateral stenosis (8 right and 10 left) and 2 had bilateral stenoses. The interhemispheric (left-right) TTP delays measured for the whole brain volume identified impaired perfusion in the hemisphere ipsilateral to the stenosis in 16 of the 18 patients. More than 45% of the patients had had ischemia in at least one half of their brain volume, with a TTP delay >0.5 second. The TTP and MTT delays showed strong correlations with PSV. In contrast, the correlations with the percentage of stenosis were weaker. The correlations for the PSV were strongest with the perfusion deficits (TTP and MTT delays) measured for the whole brain using our proposed algorithm (r = 0.80 and r = 0.74, respectively) rather than when measured on a single magnetic resonance angiography slice as performed in current clinical protocols (r = 0.31 and r = 0.58, respectively).

CONCLUSIONS

Interhemispheric TTP and MTT delay measured for the whole brain using PWI has provided a new tool for assessing cerebral perfusion deficits in patients with ACS. Carotid stenosis was associated with a detectable reduction in ipsilateral brain perfusion compared with the opposite hemisphere in >80% of patients. The PSV measured at the carotid stenosis using ultrasonography correlated with TTP and MTT delays and might serve as a clinically useful surrogate to brain hypoperfusion in these patients.

The Dark Side of Gadolinium: A Study of Arthrographic Contrast at Extreme Concentrations

Magnetic resonance arthrography is used to optimally image the detailed intraarticular anatomy of the joint space. A common iatrogenic complication of arthrography is the extra-articular injection of the gadolinium solution in the periarticular tissues; however, a less common complication involves the abnormal concentration of gadolinium within the prepared injectate. The following describes the inadvertent injection of a hyper-concentrated intraarticular solution of gadolinium and the subsequent appearance that resulted in the post-procedure magnetic resonance imaging examination. In addition, an in-vitro experiment was performed to determine the exact etiology of the abnormal magnetic resonance imaging findings that resulted in this case. The subsequent discussion revisits the signal intensity of gadolinium at extreme concentration ranges and proposes modifications of procedure protocol to mitigate the chance of a repeat event.

Brain DSC MR Perfusion in Children: A Clinical Feasibility Study Using Different Technical Standards of Contrast Administration

BACKGROUND AND PURPOSE

Dynamic susceptibility contrast MR perfusion imaging has limited results in children due to difficulties in reproducing technical standards derived from adults. This prospective, multicenter study aimed to determine DSC feasibility and quality in children using custom administration of a standard dose of gadolinium.

MATERIALS AND METHODS

Eighty-three consecutive children with brain tumors underwent DSC perfusion with a standard dose of gadobutrol administered by an automated power injector. The location and size of intravenous catheters and gadobutrol volume and flow rates were reported, and local and/or systemic adverse effects were recorded. DSC was qualitatively evaluated by CBV maps and signal intensity-time curves and quantitatively by the percentage of signal drop and full width at half-maximum, and the data were compared with the standards reported for adults. Quantitative data were grouped by flow rate, and differences among groups were assessed by analysis of covariance and tested for statistical significance with a t test.

RESULTS

No local or systemic adverse events were recorded independent of catheter location (63 arm, 14 hand, 6 foot), size (24-18 ga), and flow rates (1-5 mL/s). High-quality CBV maps and signal intensity-time curves were achieved in all patients, and quantitative evaluations were equal or superior to those reported for adults. No significant differences (P ≥ .05) were identified among the higher-flow-rate groups in the quantitative data.

CONCLUSIONS

A custom administration of a standard dose of gadobutrol allows safe and high-quality DSC MR perfusion imaging in children.

Inter-individual Comparison of Gadobutrol and Gadoteridol Tissue Time-intensity Profiles for Dynamic Susceptibility Contrast Perfusion MR Imaging

Purpose:

Gadobutrol is a gadolinium-based contrast material (GBCM) with a high concentration of gadolinium and high relaxivity. Our purpose was to evaluate the signal intensity profiles in brain tissue for the bolus width and degree of signal change after bolus injection using an echo planar dynamic susceptibility contrast (DSC) sequence. We compared gadobutrol to gadoteridol using various injection speeds and saline flush volumes.

Methods:

We studied 97 patients who underwent brain MRI. Datasets for perfusion studies were acquired using a 3T scanner with an echo planar imaging (EPI) sequence. The injection protocols were set up with combinations of injection speed and saline flush volume for both gadobutrol and gadoteridol. The full width at half maximum (FWHM) and the maximum signal change ratio (SCR_max ) of the time intensity curves were measured.

Results:

The FWHM did not show a statistically significant difference according to injection speed, flush volume, or type of GBCM. The SCR_max showed a greater change with a faster injection speed, larger saline flush, and gadobutrol administration. The difference between gadobutrol and gadoteridol became smaller with a faster injection speed and a larger saline flush.

Conclusion:

The maximum signal drop was larger with gadobutrol when the injection speed was slow and the saline flush was small. Thus, gadobutrol may be useful to obtain a better profile for DSC perfusion MRI in conditions requiring a slower injection speed and/or a smaller volume of saline flush.

Novel Magnetic Resonance Imaging Techniques in Brain Tumors

Magnetic resonance imaging is a powerful, noninvasive imaging technique with exquisite sensitivity to soft tissue composition. Magnetic resonance imaging is primary tool for brain tumor diagnosis, evaluation of drug response assessment, and clinical monitoring of the patient during the course of their disease. The flexibility of magnetic resonance imaging pulse sequence design allows for a variety of image contrasts to be acquired, including information about magnetic resonance-specific tissue characteristics, molecular dynamics, microstructural organization, vascular composition, and biochemical status. The current review highlights recent advancements and novel approaches in MR characterization of brain tumors.

Gadolinium contrast agents for CNS imaging: current concepts and clinical evidence

SUMMARY

The aim of this article was to review the properties of the various gadolinium-based contrast agents used for CNS imaging along with the clinical evidence and published data that highlight the impact these different properties can have on diagnostic performance. In addition, approaches to optimizing image acquisition that take into account the different properties of specific gadolinium-based contrast agents and an extensive review of the safety profiles of the various agents are presented.

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.

Use of contrast agents in oncological imaging: magnetic resonance imaging

Magnetic resonance plays a leading role in the management of oncology patients, providing superior contrast resolution and greater sensitivity compared with other techniques, which enables more accurate tumor identification, characterization and staging. Contrast agents are widely used in clinical magnetic resonance imaging; approximately 40-50% of clinical scans are contrast enhanced. Most contrast agents are based on the paramagnetic gadolinium ion Gd3+, which is chelated to avoid the toxic effects of free gadolinium. Multiple factors such as molecule structure, molecule concentration, dose, field strength and temperature determine the longitudinal and transverse relaxation rates (R1 and R2, respectively) and thus the T1- and T2-relaxivities of these chelates. These T1- and T2-relaxivities, together with their pharmacokinetic properties (i.e. distribution and concentration in the area of interest), determine the radiologic efficacy of the gadolinium-based contrast agents.

Dynamic and static magnetic resonance angiography of the supra-aortic vessels at 3.0 T: intraindividual comparison of gadobutrol, gadobenate dimeglumine, and gadoterate meglumine at equimolar dose

PURPOSE

The purpose of this study was the intraindividual comparison of a 1.0 M and two 0.5 M gadolinium-based contrast agents (GBCA) using equimolar dosing in dynamic and static magnetic resonance angiography (MRA) of the supra-aortic vessels.

MATERIALS AND METHODS

In this institutional review board-approved study, a total of 20 healthy volunteers (mean ± SD age, 29 ± 6 years) underwent 3 consecutive supra-aortic MRA examinations on a 3.0 T magnetic resonance system. The order of GBCA (Gadobutrol, Gadobenate dimeglumine, and Gadoterate meglumine) was randomized with a minimum interval of 48 hours between the examinations. Before each examination and 45 minutes after each examination, circulatory parameters were recorded. Total GBCA dose per MRA examination was 0.1 mmol/kg with a 0.03 mmol/kg and 0.07 mmol/kg split for dynamic and static MRA, respectively, injected at a rate of 2 mL/s. Two blinded readers qualitatively assessed static MRA data sets independently using pairwise rankings (superior, inferior, and equal). In addition, quantitative analysis was performed with signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) evaluation as well as vessel sharpness analysis of static MRA using an in-house-developed semiautomated tool. Dynamic MRA was evaluated for maximal SNR. Statistical analysis was performed using the Cohen κ, the Wilcoxon rank sum tests, and mixed effects models.

RESULTS

No significant differences of hemodynamic parameters were observed. In static MRA, Gadobutrol was rated superior to Gadoterate meglumine (P < 0.05) and equal to Gadobenate dimeglumine (P = 0.06) with good to excellent reader agreement (κ, 0.66-0.83). In static MRA, SNR was significantly higher using 1.0 M Gadobutrol as compared with either 0.5 M agent (P < 0.05 and P < 0.05) and CNR was significantly higher as compared with Gadoterate meglumine (P < 0.05), whereas CNR values of Gadobutrol data sets were not significantly different as compared with Gadobenate dimeglumine (P = 0.13). Differences in CNR between Gadobenate dimeglumine and Gadoterate meglumine were not significant (P = 0.78). Differences in vessel sharpness between the different GBCAs were also not significant (P > 0.05). Maximal SNR in dynamic MRA using Gadobutrol was significantly higher than both comparators at the level of the proximal and distal internal carotid artery (P < 0.05 and P < 0.05; P < 0.05 and P < 0.05).

CONCLUSIONS

At equimolar doses, 1.0 M Gadobutrol demonstrates higher SNR/CNR than do Gadobenate dimeglumine and Gadoterate meglumine, with superior image quality as compared with Gadoterate meglumine for dynamic and static carotid MRA. Despite the shortened bolus with Gadobutrol, no blurring of vessel edges was observed.

Perfusion MRI: the five most frequently asked technical questions

OBJECTIVE

This and its companion article address the 10 most frequently asked questions that radiologists face when planning, performing, processing, and interpreting different MR perfusion studies in CNS imaging.

CONCLUSION

Perfusion MRI is a promising tool in assessing stroke, brain tumors, and patients with neurodegenerative diseases. Most of the impediments that have limited the use of perfusion MRI can be overcome to allow integration of these methods into modern neuroimaging protocols.

Advanced techniques using contrast media in neuroimaging

This article presents an overview of advanced magnetic resonance (MR) imaging techniques using contrast media in neuroimaging, focusing on T2*-weighted dynamic susceptibility contrast MR imaging and T1-weighted dynamic contrast-enhanced MR imaging. Image acquisition and data processing methods and their clinical application in brain tumors, stroke, dementia, and multiple sclerosis are discussed.

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.

Prospective comparison of image quality and diagnostic accuracy of 0.5 molar gadobenate dimeglumine and 1.0 molar gadobutrol in contrast-enhanced run-off magnetic resonance angiography of the lower extremities

PURPOSE

To compare image quality and diagnostic accuracy of 0.5 molar gadobenate dimeglumine and 1.0 molar gadobutrol in contrast-enhanced (CE) magnetic resonance angiography (MRA) of the lower extremities interindividually.

MATERIALS AND METHODS

The study was approved by our Institutional Review Board. Written informed consent was obtained from all patients before enrollment in the study. We prospectively included 74 patients (21 women, 53 men; mean age ± SD: 67.9 ± 11.0 years) with suspected peripheral occlusive vascular disease. All patients underwent a contrast-enhanced MRA of both lower extremities with either 0.1 mL/kg body weight gadobutrol or gadobenate dimeglumine. Image quality, stenosis grade, and artifacts were assessed by two blinded, independent investigators. Signal intensity (SI), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were measured by a third investigator. Contrast agent groups were compared to each other using a two-sided Student's t-test.

RESULTS

The results did not show significant differences for SI, SNR, or CNR. Both investigators were in significant accordance (P < 0.05) with regard to stenosis detection.

CONCLUSION

We conclude that application of standard clinical doses (0.1 mL/kg body weight) of both contrast agents provides similar diagnostic results and gadolinium dose could be reduced by the application of a single dose of gadobenate dimeglumine for CE run-off MRA.

Advanced Contrast-Enhanced MR Imaging of the CNS

One of the most frequent uses of magnetic resonance imaging (MRI) since its introduction has been in the assessment of the CNS for neoplasm. In recent years there has been a substantial improvement in the MR protocol for tumors that includes the use of functional imaging techniques. As shown in multiple experimental and clinical studies an optimized use of high quality contrast media and the introduction of these functional MRI methods has improved the detection and delineation of CNS tumors. This results not only in more confident diagnoses, but also in a substantially improved differential diagnostic process. The article reviews and summarizes the technical advances in functional techniques and their impact on the assessment of cerebral pathologies, namely brain tumors, and gives practical information on how to optimize sequence parameters to achieve the optimal tissue and pathology contrast.

High-relaxivity contrast-enhanced magnetic resonance neuroimaging: a review

Evaluation of brain lesions using magnetic resonance imaging (MRI) provides information that is critical for accurate diagnosis, prognosis, therapeutic intervention and monitoring response. Conventional contrast-enhanced MR neuroimaging using gadolinium (Gd) contrast agents primarily depicts disruption of the blood-brain barrier, demonstrating location and extent of disease, and also the morphological details at the lesion site. However, conventional imaging results do not always accurately predict tumour aggressiveness. Advanced functional MRI techniques such as dynamic contrast-enhanced perfusion-weighted imaging utilise contrast agents to convey physiological information regarding the haemodynamics and neoangiogenic status of the lesion that is often complementary to anatomical information obtained through conventional imaging. Most of the Gd contrast agents available have similar T1 and T2 relaxivities, and thus their contrast-enhancing capabilities are comparable. Exceptions are gadobenate-dimeglumine, Gd-EOB-DTPA, Gadobutrol and gadofosveset, which, owing to their transient-protein-binding capability, possess almost twice (and more) the T1 and T2 relaxivities as other agents at all magnetic field strengths. Numerous comparative studies have demonstrated the advantages of the increased relaxivity in terms of enhanced image contrast, image quality and diagnostic confidence. Here we summarise the benefits of higher relaxivity for the most common neuroimaging applications including MRI, perfusion-weighted imaging and MRA for evaluation of brain tumours, cerebrovascular disease and other CNS lesions.

Diagnostic yield of double-dose gadobutrol in the detection of brain metastasis: intraindividual comparison with double-dose gadopentetate dimeglumine

BACKGROUND AND PURPOSE

Accurate assessment of the number and lesion characteristics of brain metastasis is very important in GKS. The purpose of this study was to compare the diagnostic efficacy of DD gadobutrol in the detection of brain metastases compared with a DD 0.5-mol/L gadolinium contrast, gadopentetate dimeglumine.

MATERIALS AND METHODS

Records of 27 patients (male to female ratio, 15:12; mean age, 57.1 years) diagnosed with brain metastasis and having undergone GKS were retrospectively analyzed. All patients underwent the first 3D-T1-GRE MR imaging with a DD of gadopentetate dimeglumine. The second MR imaging with a DD of gadobutrol was performed during GKS by using the same parameters used for the first scan. Two neuroradiologists counted the number of enhancing lesions on 2 consecutive MR imaging examinations and reached consensus. Lesion-brain CNR was measured from 45 lesions, and paired t test analysis was performed between DD gadopentetate dimeglumine and gadobutrol MR imaging.

RESULTS

On DD gadopentetate dimeglumine-enhanced images, a total of 130 lesions were detected visually. With DD gadobutrol, 25 additional lesions were detected on GKS MR imaging. There was no missing lesion on DD gadobutrol MR imaging. The mean lesion-brain CNR was higher on DD gadobutrol MR imaging than on DD gadopentetate dimeglumine imaging (2.17 +/- 0.19 versus 1.90 +/- 0.26; P = .00011, paired t test, 2-tailed). Only 2 cases showed lower CNR on DD gadobutrol images: 1 with hemorrhagic metastasis from renal cell carcinoma and the other with steroid treatment after the first MR imaging.

CONCLUSIONS

DD 1.0-mol/L gadobutrol provides higher lesion conspicuity and enhances lesion detection in brain metastasis compared with DD 0.5-mol/L gadolinium contrast agents.

Extracellular gadolinium-based contrast media: differences in diagnostic efficacy

Since the introduction of the first gadolinium-based contrast agent (Gd-CA) in 1988 it has become clear that these agents significantly improve the diagnostic efficacy of MRI. Studies on single agents have shown that, in comparison to unenhanced sequences, all agents help to improve the detection and delineation of lesions which can alter diagnosis in up to 40% of patients. Doubling or tripling the standard dose of 0.1 mmol/kg body weight may be beneficial for selected indications (e.g. brain perfusion, equivocal single dose study in MRI for brain metastasis, small vessel MR angiography). A more limited number of studies have compared the various agents. These studies do not show clinically significant differences in diagnostic efficacy between the various extracellular Gd-CA. Agents with higher concentration or protein binding may be relatively better suitable for selected applications (e.g. perfusion MRI). The higher relaxivity agents may be used in somewhat lower doses than the extracellular agents.

Variable echo time imaging: signal characteristics of 1-M gadobutrol contrast agent at 1.5 and 3T

Gadobutrol (Gd-Bt; Gadovist(R), Schering AG) is a 1-M Gadolinium (Gd)-based contrast agent. Its higher Gd concentration allows for reduction of injection volumes in first pass contrast-enhanced MR angiography (CE-MRA) and should increase bolus sharpness and image quality. However, ambivalent results were reported. In order to explore the performance of 1-M contrast agents such as Gd-Bt and its dependence on molecular environment and temperature, signal characteristics were analyzed for a series of increasing Gd-Bt concentrations for different temperature-controlled samples in water and human blood plasma. Relaxation times, relaxivities, and signal-concentration curves were assessed for several Gd-Bt concentrations in water at 20 degrees C and 37 degrees C and in plasma at 37 degrees C for 1.5T and 3T. Gd-Bt concentration influence on signal intensity (SI) could be effectively simulated and compared with experimental measurements as well as simulations with other contrast agents at realistic in vivo concentrations. Particular attention was given to T(2)- and T(*) (2)-induced losses at high concentrations, which annihilate benefits from T(1) shortening. Based on these findings, variable echo time (VTE) approaches with readout bandwidth varying with k-space position were explored in order to enhance the signal to noise performance of gradient echo imaging at high contrast agent concentrations. Results indicate the potential of VTE for imaging with increased SNR at high contrast agent concentrations.

A serial dilution study of gadolinium-based MR imaging contrast agents

BACKGROUND AND PURPOSE

With the approval of gadobenate dimeglumine, higher relaxivity MR contrast agents were introduced into the clinical environment, and multiple in vivo studies compared the efficacy and safety with the previously approved agents. An in vitro study was conducted to demonstrate differences between the various agents to confirm published values and for imaging-sequence optimization.

MATERIALS AND METHODS

A contrast phantom was made with serial dilutions of commercially available formulations of 5 US Food and Drug Administration-approved gadolinium-based MR imaging contrast agents in human serum substitute. Dilution factors ranging from 1:8 to 1:4096 were included in the phantom. Spin-echo sequences were performed at 1.5T and 3T with varying TRs and TEs.

RESULTS

At physiologic concentrations and by using short TRs and TEs, gadobenate demonstrated the highest signal intensities, confirming greater R1 relaxivity. At higher concentrations and with longer TR and TE values, the greatest signal intensity loss was appreciated for gadobenate, confirming greater R2 relaxivity.

CONCLUSION

Using rigorous in vitro methodology and serial dilution techniques, this study confirms the reported higher R1 and R2 relaxivities of gadobenate relative to the other agents at 1.5T and 3T.

Basics of Magnetic Resonance Imaging and Magnetic Resonance Spectroscopy

In this chapter, the basic principles of magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) (Sects. 2.2, 2.3, and 2.4), the technical components of the MRI scanner (Sect. 2.5), and the basics of contrast agents and the application thereof (Sect. 2.6) are described. Furthermore, flow phenomena and MR angiography (Sect. 2.7) as well as diffusion and tensor imaging (Sect. 2.7) are elucidated.

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.

Advances in magnetic resonance (2007)

Advances in clinical magnetic resonance (MR) are discussed in this review in the context of publications from Investigative Radiology during 2006 and 2007. The articles relevant to this topic, published during this 2 year time period, are considered as organized by anatomic region. An additional final focus of discussion is in regards to those studies involving MR contrast media.

Comparison of different iodine concentration contrast media in perfusion computed tomography of the brain: is high iodine concentration useful?

OBJECTIVES

To investigate maximum enhancement and visual map quality in cerebral perfusion computed tomography (PCT) with variation of iodine concentration of contrast media (CM).

MATERIALS AND METHODS

Two groups of 45 patients each, underwent PCT with either 370 mg iodine/mL (30 mL; 6 mL/s) or 300 mg iodine/mL (40 mL; 8 mL/s) CM, respectively, and similar total iodine dose. Parenchymal and vascular enhancement as well as contrast-to-noise ratio of superior sagittal sinus was measured on PCT source images. PCT maps were rated visually with dichotomized scale for diagnostic quality.

RESULTS

Enhancement and contrast-to-noise ratio of the superior sagittal sinus was significantly higher for the 370 mg iodine/mL protocol (P < 0.0002 and P < 0.007), whereas parenchymal enhancement was not significantly different. Diagnostic quality of PCT maps did not differ between both protocols (P < 0.557).

CONCLUSIONS

PCT using 370 mg iodine/mL CM can be reliably performed with reduced injection rate and less total volume enabling smaller diameter of intravenous canula compared with 300 mg iodine/mL CM.

Value of cerebral perfusion computed tomography in the management of intensive care unit patients with suspected ischaemic cerebral pathology after cardiac surgery

OBJECTIVE

Adverse neurologic outcomes, like stroke, in intensive care unit (ICU) patients after cardiac surgery can have devastating consequences, among them increased mortality risk and, among survivors, loss of independence and a diminished quality of life. Non-contrast computed tomography (CT) remains a widely utilised modality for assessing stroke; however, it has a low sensitivity in the acute phase. Perfusion CT (PCT) has the potential of imaging stroke in its hyperacute phase. We evaluated the feasibility and results of the method among patients from the ICU.

METHODS

The NCCT and PCT images of 33 retrospectively identified patients were included in this study. The diagnostic contribution of the PCT to patient management was classified according to one of three categories: (A) those that changed the preliminary (NCCT) diagnosis; (B) those that revealed additional pathology and/or specified more exactly findings that have been detected by NCCT or clinically suspected; and (C) confirmed the preliminary diagnosis. Neurologic outcome variables were also documented and associated with PCT lesions.

RESULTS

Fifteen patients after coronary artery bypass graft (CABG) operation, 14 patients after CABG and valve surgery, and 4 patients after an aortic dissection (Type A) surgery underwent a NCCT with PCT 2.4+/-1.3 days after the operation. Twenty patients had bilateral internal carotid artery (ICA) stenosis (>50%), 11 patients had unilateral ICA stenosis (>75%), and 2 patients had no ICA stenosis. In nine patients (27.2%) the PCT changed the initial diagnosis of the NCCT and revealed ischaemic pathology. In 24 patients (72.7%), the performed PCT revealed additional pathology and/or more completely characterised findings that have been detected by the initial NCCT. In nine patients, PCT confirmed only the initial diagnosis. Patients with normal PCT findings had a favourable outcome; patients with large lesions in PCT in one or more vascular territories had an unfavourable outcome; seven patients with lesions in basal ganglia and/or semioval centre had a favourable outcome.

CONCLUSIONS

PCT shows a greater sensitivity in detecting and mapping acute ischaemic stroke in ICU patients (after cardiac surgery) in whom conventional imaging findings are not in line with the severity of the clinical condition.

Contrast-enhanced magnetic resonance imaging of central nervous system tumors: agents, mechanisms, and applications

Brain tumors are one of the most common neoplasms in young adults and are associated with a high mortality and disability rate. Magnetic resonance imaging (MRI) is widely accepted to be the most sensitive imaging modality in the assessment of cerebral neoplasms. Because the detection, characterization, and exact delineation of brain tumors require a high lesion contrast that depends on the signal of the lesion in relation to the surrounding tissue, contrast media is given routinely. Anatomical and functional, contrast agent-based MRI techniques allow for a better differential diagnosis, grading, and especially therapy decision, planing, and follow-up. In this article, the basics of contrast enhancement of brain tumors will be reviewed. The underlying pathology of a disrupted blood-brain barrier and drug influences will be discussed. An overview of the currently available contrast media and the influences of dosage, field strength, and application on the tumor tissue contrast will be given. Challenging, contrast-enhanced, functional imaging techniques, such as perfusion MRI and dynamic contrast-enhanced MRI, are presented both from the technical side and the clinical experience in the assessment of brain tumors. The advantages over conventional, anatomical MRI techniques will be discussed as well as possible pitfalls and drawbacks.

Effect of the Arterial Input Function on the Measured Perfusion Values and Infarct Volumetric in Acute Cerebral Ischemia Evaluated by Perfusion Computed Tomography

OBJECTIVES

We sought to evaluate the accuracy of the perfusion computed tomography (PCT) deconvolution-based brain perfusion measurements and the lesions' (infarct and penumbra) volumetric with regard to arterial input function (AIF) selection in patients with acute stroke.

MATERIALS AND METHODS

Eighteen consecutive patients with symptoms of acute stroke underwent PCT at admission. Follow-up magnetic resonance imaging was obtained in all patients after 3.6 +/- 1.7 days (range, 1.5-6 days). PCT maps were generated focusing on the anterior cerebral artery (ACA) and branches of the middle cerebral artery (MCA) ipsilateral and contralateral to the ischemic lesion as AIFs. Infarct, penumbra, and total ischemic lesion were delineated on cerebral blood flow (CBF) maps. CBF, cerebral blood volume (CBV), and mean transit time (MTT) were calculated in the ischemic regions as provided by the 3 different AIFs, the normality test was applied for the obtained parameters, and the values were correlated (Pearson's correlation coefficient). Volumes of the ischemic regions (as obtained by the different AIFs) also were correlated and compared (paired t test) to the follow-up infarct volume.

RESULTS

The CBF and CBV values obtained by the different AIFs in the infarct, penumbra, and total ischemic lesion were significantly correlated (r=0.94-0.96, P<or=0.01). Only in the infarct region calculated MTT values were correlated (r=0.88-0.91, P<0.05) between the different AIFs groups. High correlation coefficients (r=0.79-0.91, P<0.001) were observed between the admission PCT infarct and total ischemic volume and the MRI follow-up infarct volume. ACA as AIF provided the best correlations (r=0.91, P=0.0002) with the follow-up measurements. No statistically significant difference was found between the 3 different AIF-estimated admission total ischemic volumes and the follow-up infarct volume.

CONCLUSIONS

The AIF selection in the ACA as well as in the ipsilateral (to the hypoperfused area) or contralateral branches of the MCA has no statistically significant impact on the calculation of the CBF, CBV values, and the volume estimation of the ischemic region in the acute stroke patients.

Evaluation of a Novel Time-Efficient Protocol for Gadobenate Dimeglumine (Gd-BOPTA)-Enhanced Liver Magnetic Resonance Imaging

OBJECTIVE

We sought to evaluate gadobenate dimeglumine for the detection and characterization of focal liver lesions in the unenhanced and already pre-enhanced liver.

MATERIALS AND METHODS

Sixty patients were evaluated prospectively. Unenhanced T1-weighted gradient echo (T1wGRE) and T2-weighted turbo spin echo (T2wTSE) images were acquired followed by contrast-enhanced T1wGRE images during the dynamic, equilibrium, and delayed phases after the bolus injection of 0.05 mmol/kg gadobenate dimeglumine. An identical series of dynamic images was then acquired after the delayed scan following a second 0.05 mmol/kg bolus of gadobenate dimeglumine. Images were evaluated randomly in 2 sessions by 3 independent blinded readers. Evaluated images in the first session comprised the unenhanced images, the first or second set of dynamic images, and the delayed images. The second session included the unenhanced images, the dynamic images not yet evaluated in the first session, and the delayed images. The 2 reading sessions were compared for lesion characterization and diagnosis, and kappa (kappa) values for interobserver agreement were determined. Quantitative evaluation of lesion contrast enhancement was also performed.

RESULTS

The enhancement behavior in the second dynamic series was similar to that in the first series, although pre-enhancement of the normal liver resulted in reduced lesion-liver contrast-to-noise ratios and the visualization of some lesions only on arterial phase images. Typical imaging features for the lesions included in the study were visualized clearly in both series. Strong agreement (kappa=0.56-0.89; all evaluations) between the 2 images sets was noted by all readers for differentiation of benign from malignant lesions and for definition of specific diagnosis, and between readers for diagnoses established based on images acquired in the unenhanced and pre-enhanced liver.

CONCLUSION

Dynamic imaging in the hepatobiliary phase gives similar information as dynamic imaging of the unenhanced liver. This might prove advantageous for screening protocols involving same session imaging of primary extrahepatic tumors and liver.

Advances in Magnetic Resonance (2006)

Advances in the field of magnetic resonance (MR) as it pertains to clinical diagnostic radiology are examined in this review on the basis of publications in Investigative Radiology over the past 2 years (2005-2006). The articles published during that timeframe are discussed, organizationally wise, by anatomic region with an additional focus on studies involving MR contrast media.

Relaxivity of Gadopentetate Dimeglumine (Magnevist), Gadobutrol (Gadovist), and Gadobenate Dimeglumine (MultiHance) in Human Blood Plasma at 0.2, 1.5, and 3 Tesla

OBJECTIVES

We sought to determine the relaxivity and accurate relaxation rates of Gd-DTPA, Gd-BT-DO3A, and Gd-BOPTA at 0.2, 1.5, and 3 T in human blood plasma.

MATERIALS AND METHODS

Contrast media concentrations between 0.01 and 16 mM in human plasma were used for relaxation measurements. The R1 and R2 relaxation rates and r1 and r2 relaxivities were determined.

RESULTS

Gd-BOPTA produced the highest relaxation rates and relaxivities at all field strengths. The r1 and r2 values for Gd-BOPTA were 107-131% and 91-244% higher than for Gd-DTPA, respectively, and 72-98% and 82-166% higher than for Gd-BT-DO3A. Higher field strengths resulted in lower values of R1, R2, and r1 for all contrast agents tested and of r2 for Gd-DTPA and Gd-BT-DO3A. A linear dependence of R1 and R2 on concentration was found for Gd-DTPA and Gd-BT-DO3A and a nonlinear dependence for Gd-BOPTA for concentrations larger than 1 mM. The r1 and r2 relaxivity of Gd-BOPTA increased with decreasing concentration.

CONCLUSIONS

Gd-BOPTA demonstrates the highest longitudinal r1 at all field strengths, which is ascribable to weak protein interaction. The R2/R1 ratio increases at higher field strength only for Gd-BOPTA, hence very short echo times are required for Gd-BOPTA to benefit from the higher longitudinal relaxivity.