Vessel Type Determined by Vessel Architectural Imaging Improves Differentiation between Early Tumor Progression and Pseudoprogression in Glioblastoma

BACKGROUND AND PURPOSE

Currently available perfusion parameters are limited in differentiating early tumor progression and pseudoprogression with no insight about vessel size and type. We aimed to investigate differences in vessel size and type between early tumor progression and pseudoprogression in posttreatment glioblastoma and to demonstrate diagnostic performance using vessel architectural imaging.

MATERIALS AND METHODS

Fifty-eight patients with enlarging contrast-enhancing masses in posttreatment glioblastomas underwent simultaneous gradient recalled-echo and spin-echo dynamic susceptibility contrast imaging. Relative CBV and vessel architectural imaging parameters, including the relative vessel size index, peak shift between gradient recalled echo and spin-echo bolus signal peaks, and arterial dominance scores using spatial dominance of arterial/venous vessel type, were calculated and compared between the 2 conditions. The area under the curve and cross-validation were performed to compare the diagnostic performance of the relative CBV, vessel architectural imaging parameters, and their combinations.

RESULTS

There were 41 patients with early tumor progression and 17 patients with pseudoprogression. Relative to pseudoprogression, early tumor progression showed a lower peak shift (-0.02 versus 0.33, P = .02) and a lower arterial dominance score (1.46 versus 2.11, P = .001), indicating venous dominance. Patients with early tumor progression had higher relative CBV (1.88 versus 1.38, P = .02) and a tendency toward a larger relative vessel size index (99.67 versus 83.17, P = .15) than those with pseudoprogression. Combining arterial dominance scores and relative CBV showed significantly higher diagnostic performance (area under the curve = 0.82; 95% CI, 0.70-0.94; P = .02) than relative CBV alone (area under the curve = 0.64; 95% CI, 0.49-0.79) in distinguishing early tumor progression from pseudoprogression.

CONCLUSIONS

Vessel architectural imaging significantly improved the diagnostic performance of relative CBV by demonstrating venous dominance and a tendency toward larger vessel size in early tumor progression.

Methylphenidate Effects on Cortical Thickness in Children and Adults with Attention-Deficit/Hyperactivity Disorder: A Randomized Clinical Trial

BACKGROUND AND PURPOSE

Although methylphenidate is frequently used to treat children with attention-deficit/hyperactivity disorder, it is currently unknown how methylphenidate affects brain development. In a randomized controlled trial, we investigated whether the cortical effects of methylphenidate are modulated by age.

MATERIALS AND METHODS

Between June 1, 2011, and June 15, 2015, we conducted a randomized, double-blind, placebo-controlled trial (Effects of Psychotropic Drugs on Developing Brain-Methylphenidate) in 99 males with attention-deficit/hyperactivity disorder (according to Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, criteria) from referral centers in the greater Amsterdam area in the Netherlands. The trial was registered on March 24, 2011 (identifier NL34509.000.10) and subsequently at the Netherlands National Trial Register (identifier NTR3103). Participants (first enrolled October 13, 2011) were 10-12 years or 23-40 years of age and randomized to treatment with either methylphenidate or a placebo for 16 weeks. Our main outcome was a change in cortical thickness in predefined ROIs as measured by MR imaging pre- and posttreatment.

RESULTS

We observed a time × medication × age interaction (F[1,88.825] = 4.316, P < .05) for the right medial cortex ROI, where methylphenidate treatment yielded less cortical thinning in children, but not in adults or the placebo groups.

CONCLUSIONS

Our finding that the effects of methylphenidate on right medial cortical thickness differ between children and adults infers that the drug affects gray matter development in this brain region. This warrants replication in larger groups with longer follow-up to determine whether this effect can also be observed in other cortical brain regions and whether it may have long-term consequences.

Clinical Value of Vascular Permeability Estimates Using Dynamic Susceptibility Contrast MRI: Improved Diagnostic Performance in Distinguishing Hypervascular Primary CNS Lymphoma from Glioblastoma

BACKGROUND AND PURPOSE

A small subset of primary central nervous system lymphomas exhibits high cerebral blood volume, which is indistinguishable from that in glioblastoma on dynamic susceptibility contrast MR imaging. Our study aimed to test whether estimates of combined perfusion and vascular permeability metrics derived from DSC-MR imaging can improve the diagnostic performance in differentiating hypervascular primary central nervous system lymphoma from glioblastoma.

MATERIALS AND METHODS

A total of 119 patients (with 30 primary central nervous system lymphomas and 89 glioblastomas) exhibited hypervascular foci using the reference method of leakage-corrected CBV (reference-normalized CBV). An alternative postprocessing method used the tissue residue function to calculate vascular permeability (extraction fraction), leakage-corrected CBV, cerebral blood flow, and mean transit time. Parameters were compared using Mann-Whitney U tests, and the diagnostic performance to distinguish primary central nervous system lymphoma from glioblastoma was calculated using the area under the curve from the receiver operating characteristic curve and was cross-validated with bootstrapping.

RESULTS

Hypervascular primary central nervous system lymphoma showed similar leakage-corrected normalized CBV and leakage-corrected CBV compared with glioblastoma (P > .05); however, primary central nervous system lymphoma exhibited a significantly higher extraction fraction (P < .001) and CBF (P = .01) and shorter MTT (P < .001) than glioblastoma. The extraction fraction showed the highest diagnostic performance (the area under the receiver operating characteristic curve [AUC], 0.78; 95% confidence interval, 0.69-0.85) for distinguishing hypervascular primary central nervous system lymphoma from glioblastoma, with a significantly higher performance than both CBV (AUC, 0.53-0.59, largest P = .02) and CBF (AUC, 0.72) and MTT (AUC, 0.71).

CONCLUSIONS

Estimation of vascular permeability with DSC-MR imaging further characterizes hypervascular primary central nervous system lymphoma and improves diagnostic performance in glioblastoma differentiation.

Improved Automatic Segmentation of White Matter Hyperintensities in MRI Based on Multilevel Lesion Features

Brain white matter hyperintensities (WMHs) are linked to increased risk of cerebrovascular and neurodegenerative diseases among the elderly. Consequently, detection and characterization of WMHs are of significant clinical importance. We propose a novel approach for WMH segmentation from multi-contrast MRI where both voxel-based and lesion-based information are used to improve overall performance in both volume-oriented and object-oriented metrics. Our segmentation method (AMOS-2D) consists of four stages following a "generate-and-test" approach: pre-processing, Gaussian white matter (WM) modelling, hierarchical multi-threshold WMH segmentation and object-based WMH filtering using support vector machines. Data from 28 subjects was used in this study covering a wide range of lesion loads. Volumetric T1-weighted images and 2D fluid attenuated inversion recovery (FLAIR) images were used as basis for the WM model and lesion masks defined manually in each subject by experts were used for training and evaluating the proposed method. The method obtained an average agreement (in terms of the Dice similarity coefficient, DSC) with experts equivalent to inter-expert agreement both in terms of WMH number (DSC = 0.637 vs. 0.651) and volume (DSC = 0.743 vs. 0.781). It allowed higher accuracy in detecting WMH compared to alternative methods tested and was further found to be insensitive to WMH lesion burden. Good agreement with expert annotations combined with stable performance largely independent of lesion burden suggests that AMOS-2D will be a valuable tool for fully automated WMH segmentation in patients with cerebrovascular and neurodegenerative pathologies.

NMR relaxation studies with MnDPDP

Purpose: Our studies were designed to compare the efficacy of mangafodipir triso-dium (MnDPDP, Teslascan) as a tissue-specific MR agent with that of manganese chloride (MnCl2), to compare the efficacy of different doses and rates of administration of MnDPDP, and to collect the data needed for predicting optimum pulse sequences.

Material and Methods: The dose response for the relaxation rates R1 and R2 at 0.47 T, and the manganese (Mn) concentrations in rat liver and in the liver, pancreas, heart and adrenals of pigs was determined for both MnDPDP and MnCl2 administered i.v. Computer simulations were carried out to model the effects of different tissue Mn concentrations and TR on signal intensities and contrast-to-noise ratios.

Results: In rat liver and pig organs both compounds produced a positive dose-response in R1 and tissue Mn concentration, and only small or no response in R2. The Mn concentration in rat liver was positively correlated with R1, regardless of the form in which Mn was given, or the rate of administration. Optimal imaging parameters are therefore expected to be different pre- and post-MnDPDP administration.

Conclusion: The added cardiovascular safety of MnDPDP compared with MnCl2 does not result in loss of efficacy in increasing R1 at the intended clinical dose of 5 μmol/kg MnDPDP. The changes in R2 were too small to affect T2-weighted images. The data give the basis for choosing the appropriate pulse sequences for MnDPDP-en-hanced MR imaging.

Neurobiological correlates of depressive symptoms in people with subjective and mild cognitive impairment

OBJECTIVE

To test the hypothesis that depressive symptoms correlate with Alzheimer's disease (AD) type changes in CSF and structural and functional imaging including hippocampus volume, cortical thickness, white matter lesions, Diffusion tensor imaging (DTI), and fluoro-deoxy-glucose positron emission tomography (FDG-PET) in patient with subjective (SCI) and mild (MCI) cognitive impairment.

METHOD

In 60 patients, depressive symptoms were assessed using the Geriatric Depression Scale. The subjects underwent MRI, 18F-FDG PET imaging, and lumbar CSF extraction.

RESULTS

Subjects with depressive symptoms (n=24) did not have more pathological AD biomarkers than non-depressed. Uncorrected there were trends towards larger hippocampal volumes (P=0.06), less orbital WM damage measured by DTI (P=0.10), and higher orbital glucose metabolism (P=0.02) in the depressed group. The findings were similar when SCI and MCI were analyzed separately. Similarly, in patients with pathological CSF biomarkers (i.e., predementia AD, n=24), we found that correlations between scores on GDS and CSF Aß42 and P-tau indicated less severe AD-specific CSF changes with increasing depression.

CONCLUSION

Depressive symptoms are common in SCI/MCI, but are not associated with pathological imaging or CSF biomarkers of AD. Depression can explain cognitive impairment in SCI/MCI or add to cognitive impairment leading to an earlier clinical investigation in predementia AD.

White matter characteristics and cognition in prenatally opiate- and polysubstance-exposed children: a diffusion tensor imaging study

BACKGROUND AND PURPOSE

Prenatal drug exposure may influence the developing brain. Our aim was to study WM characteristics with DTI in children with prenatal opiate and polysubstance exposure and in controls. We assessed whether group differences in FA, DA, and DR could be found and related to cognitive function.

MATERIALS AND METHODS

The study was approved by a committee for medical research ethics. Parents signed an informed consent; children gave spoken consent. Our sample included 14 prenatally substance-exposed adopted children (5 girls; age range, 8.6-13.9 years; mean, 11.3 +/- 1.7 years) and 14 control children (7 girls; age range, 9.0-10.2 years; mean, 9.8 +/- 0.3 years). Tract-based spatial statistics were used to define a common WM skeleton for the sample, and FA was compared between groups throughout the skeleton, controlling for age and sex. Clusters of significant group differences >or=100 voxels (P <. 05) were identified. FA, DA, and DR within clusters were correlated with cognitive function.

RESULTS

Ten clusters of FA group differences, mostly in central, posterior, and inferior parts of the brain, were identified (P <. 05), showing lower FA in substance-exposed children. FA and DA correlated positively and DR, negatively with cognitive function across groups.

CONCLUSIONS

Prenatally substance-exposed children exhibited lower FA in restricted areas of WM, mostly relatively central, inferior, and posterior, where myelination occurs early in development. Myelin in these areas may be particularly vulnerable to prenatal substance exposure. FA and DR related moderately to cognitive function. Potential confounding factors existed and were considered.

Multimodal imaging in mild cognitive impairment: Metabolism, morphometry and diffusion of the temporal-parietal memory network

This study compared sensitivity of FDG-PET, MR morphometry, and diffusion tensor imaging (DTI) derived fractional anisotropy (FA) measures to diagnosis and memory function in mild cognitive impairment (MCI). Patients (n=44) and normal controls (NC, n=22) underwent FDG-PET and MRI scanning yielding measures of metabolism, morphometry and FA in nine temporal and parietal areas affected by Alzheimer's disease and involved in the episodic memory network. Patients also underwent memory testing (RAVLT). Logistic regression analysis yielded 100% diagnostic accuracy when all methods and ROIs were combined, but none of the variables then served as unique predictors. Within separate ROIs, diagnostic accuracy for the methods combined ranged from 65.6% (parahippocampal gyrus) to 73.4 (inferior parietal cortex). Morphometry predicted diagnostic group for most ROIs. PET and FA did not uniquely predict group, but a trend was seen for the precuneus metabolism. For the MCI group, stepwise regression analyses predicting memory scores were performed with the same methods and ROIs. Hippocampal volume and FA of the retrosplenial WM predicted learning, and hippocampal metabolism and parahippocampal cortical thickness predicted 5 minute recall. No variable predicted 30 minute recall independently of learning. In conclusion, higher diagnostic accuracy was achieved when multiple methods and ROIs were combined, but morphometry showed superior diagnostic sensitivity. Metabolism, morphometry and FA all uniquely explained memory performance, making a multi-modal approach superior. Memory variation in MCI is likely related to conversion risk, and the results indicate potential for improved predictive power by the use of multimodal imaging.

A piglet model for detection of hypoxic-ischemic brain injury with magnetic resonance imaging

Munkeby BH, de Lange C, Emblem KE, Bjørnerud A, Kro GAB, Andresen J, Winther-Larssen EH, Løberg EM, Hald JK. A piglet model for detection of hypoxic-ischemic brain injury with magnetic resonance imaging. Acta Radiol 2008;49:1049–1057.

Quantitative renal cortical perfusion in human subjects with magnetic resonance imaging using iron-oxide nanoparticles: influence of T1 shortening

BACKGROUND

Using conventional contrast agents, the technique of quantitative perfusion by observing the transport of a bolus with magnetic resonance imaging (MRI) is limited to the brain due to extravascular leakage.

PURPOSE

To perform quantitative perfusion measurements in humans with an intravascular contrast agent, and to estimate the influence of the T1 relaxivity of the contrast agent on the first-pass response.

MATERIAL AND METHODS

Renal cortical perfusion was measured quantitatively in six patients with unilateral renal artery stenosis using a rapid gradient double-echo sequence in combination with an intravenous bolus injection of NC100150 Injection, an intravascular contrast agent based on iron-oxide nanoparticles. The influence of T1 relaxivity was measured by comparing perfusion results based on single- and double-echo data.

RESULTS

The mean values of cortical blood flow, cortical blood volume, and mean transit time in the normal kidneys were measured to 339+/-60 ml/min/100 g, 41+/-8 ml/100 g, and 7.3+/-1.0 s, respectively, based on double-echo data. The corresponding results based on single-echo data, which are not compensated for the T1 relaxivity, were 254+/-47 ml/min/100 g, 27+/-3 ml/100 g, and 6+/-1.2 s, respectively.

CONCLUSION

The use of a double-echo sequence enabled elimination of confounding T1 effects and consequent systematic underestimation of the perfusion.

Morphometric changes in the episodic memory network and tau pathologic features correlate with memory performance in patients with mild cognitive impairment

BACKGROUND AND PURPOSE

Mild cognitive impairment (MCI) may affect several cognitive domains, including attention and reasoning, but is often first characterized by memory deficits. The purpose of this study was to ask these 2 questions: 1) Can levels of CSF tau proteins and amyloid beta 42 peptide explain thinning of the cerebral cortex in patients with MCI? 2) How are brain morphometry, CSF biomarkers, and apolipoprotein E (APOE) allelic variation related to episodic memory function in MCI?

MATERIALS AND METHODS

Hippocampal volume and cortical thickness were estimated by MR imaging and compared for patients with MCI (n = 18) and healthy controls (n = 18). In addition, regions of interest (ROIs) were selected in areas where the MCI group had atrophy and which overlapped with the episodic memory network (temporal, entorhinal, inferior parietal, precuneus/posterior cingulate, and frontal). Relationships among morphometry, CSF biomarkers, APOE, and memory were tested. The analyses were repeated with an independent sample of patients with MCI (n = 19).

RESULTS

Patients with MCI and pathologic CSF values had hippocampal atrophy. However, both patients with pathologic and patients with nonpathologic CSF had a thinner cortex outside the hippocampal area. CSF pathology was related to hippocampal volume, whereas relationships with cortical thickness were found mainly in one of the samples. Morphometry correlated robustly with memory performance across MCI samples, whereas less stable results were found for tau protein.

CONCLUSION

The differences in hippocampal volume between the MCI and the healthy control groups were only found in patients with pathologic CSF biomarkers, whereas differences in cortical thickness were also found for patients without such pathologic features. Morphometry in areas in the episodic memory network was robustly correlated with memory performance. It is speculated that atrophy in these areas may be associated with the memory problems seen in MCI.

Volumetric cerebral characteristics of children exposed to opiates and other substances in utero

Morphometric cerebral characteristics were studied in children with prenatal poly-substance exposure (n=14) compared to controls (n=14) without such exposure. Ten of the substance-exposed children were born to mothers who used opiates (heroin) throughout the pregnancy. Groups were compared across 16 brain measures: cortical gray matter, cerebral white matter, hippocampus, amygdala, thalamus, accumbens area, caudate, putamen, pallidum, brainstem, cerebellar cortex, cerebellar white matter, lateral ventricles, inferior lateral ventricles, and the 3rd and 4th ventricles. In addition, continuous measurement of thickness across the entire cortical mantle was performed. Volumetric characteristics were correlated with ability and questionnaire assessments 2 years prior to scan. Compared to controls, the substance-exposed children had smaller intracranial and brain volumes, including smaller cerebral cortex, amygdala, accumbens area, putamen, pallidum, brainstem, cerebellar cortex, cerebellar white matter, and inferior lateral ventricles, and thinner cortex of the right anterior cingulate and lateral orbitofrontal cortex. Pallidum and putamen appeared especially reduced in the subgroup exposed to opiates. Only volumes of the right anterior cingulate, the right lateral orbitofrontal cortex and the accumbens area, showed some association with ability and questionnaire measures. The sample studied is rare and hence small, so conclusions cannot be drawn with certainty. Morphometric group differences were observed, but associations with previous behavioral assessment were generally weak. Some of the volumetric differences, particularly thinner cortex in part of the right lateral orbitofrontal cortex, may be moderately involved in cognitive and behavioral difficulties more frequently experienced by opiate and poly-substance-exposed children.

Diaschisis after thalamic stroke: a comparison of metabolic and structural changes in a patient with amnesic syndrome

INTRODUCTION

We present a patient with a left anteromedial thalamic lesion with an amnesic syndrome. The patient underwent neuropsychological testing, cerebrospinal fluid (CSF) analyses, magnetic resonance imaging (MRI) [T2, flair, and diffusion tensor imaging (DTI)] and [18F]-2-fluoro-deoxy-d-glucose positron emission tomography (FDG-PET) to assess indirect effects of thalamic lesions on cortical function.

CASE REPORT

A 67-year-old right-handed woman was admitted to a university-based memory unit because of memory and concentration problems. Neuropsychological testing revealed dysfunction of episodic memory, semantic memory and working memory. General intellectual function and attention capacity were preserved. MRI revealed an anteromedial thalamic lesion in the left hemisphere. FDG-PET showed decreased uptake in the frontal, parietal and temporal lobes of the left hemisphere. Regions of interest (ROI) in white matter were selected and left and right hemispheres were compared. Fractional anisotropy (FA) in ROI representing thalamo-cortical connections were decreased in the left hemisphere when compared with the right.

CONCLUSION

The results show the importance of a network that include the anterior and dorsomedian nuclei, which influence the activity in areas of the cortex responsible for memory processes. The imaging findings suggest that areas of cortical diaschisis after thalamic infarction correspond to areas affected by thalamo-cortical fibre loss as measured with FA.

Contrast-enhanced dynamic magnetic resonance imaging of finger joints in osteoarthritis and rheumatoid arthritis: an analysis based on pharmacokinetic modeling

PURPOSE

To investigate a two-compartment kinetic model applied to the dynamic time course of contrast enhancement as a method to differentiate between finger-joint synovitis in established osteoarthritis (OA) and rheumatoid arthritis (RA).

MATERIAL AND METHODS

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) of one hand in 19 patients and six healthy volunteers was undertaken. Eight patients had OA of the hand and eleven patients had RA. From the signal intensity curves, the three parameters Kps (endothelial transfer constant), Kep (elimination rate constant from extracellular space back to plasma) and Kel (elimination rate constant from plasma by renal excretion) were calculated.

RESULTS

The rate constant Kps showed the best separation between the groups with significantly higher values in the RA group compared to the OA group (P<0.005) and in the OA group compared to the control group (P<0.005). Significantly higher values of Kep were also found in the RA group compared with the OA group (P<0.005).

CONCLUSION

DCE-MRI may provide useful information that can help differentiate synovitis in OA from synovitis in RA.

pH-sensitive paramagnetic liposomes as MRI contrast agents: in vitro feasibility studies

A novel type of pH-sensitive paramagnetic contrast agent is introduced; a low molecular weight gadolinium (Gd) chelate (GdDTPA-BMA) encapsulated within pH-sensitive liposomes. The in vitro relaxometric properties of the liposomal Gd chelate were shown to be a function of the pH in the liposomal dispersion and the membrane composition. Only a minor pH-dependency of the T1 relaxivity (r1) was observed for liposomal GdDTPA-BMA composed of the unsaturated lipids dioleoyl phosphatidyl ethanolamine (DOPE) and oleic acid (OA). On the other hand, the r1 of GdDTPA-BMA encapsulated within saturated dipalmitoyl phosphatidyl ethanolamine/palmitic acid (DPPE/PA) liposomes demonstrated a strong pH-dependency. At physiological pH and above, the r1 of this system was significantly lowered compared to that of non-liposomal Gd chelate, which was explained by an exchange limited relaxation process. Lowering the pH below physiological value, however, gave a sharp and 6-7 fold increase in r1, due to liposome destabilisation and subsequent leakage of entrapped GdDTPA-BMA. The pH-sensitivity of the DPPE/PA liposome system was confirmed in an in vitro magnetic resonance imaging (MRI) phantom study.

Pre-clinical results with Clariscan (NC100150 Injection); experience from different disease models

A superparamagnetic nanoparticle (NC100150 Injection) was investigated in two different animal models; renal perfusion in pigs and tumour imaging in mice. In the pig model, qualitative first-pass perfusion maps following a bolus injection of NC100150 Injection enabled good visualisation of hypoperfused regions of the renal cortex following partial ligation of the renal artery. High temporal resolution was found to be essential to accurately capture the first passage of the contrast agent through the kidney due to the very rapid blood flow in normal renal cortex. In the tumour model (LS174T cells implanted in nude mice), NC100150 Injection was found to cause a gradual (over 60 min) signal increase on T1-w images in part of the tumours which was attributed to contrast agent leakage from the vascular space to the extravascular space in areas of increased capillary permeability. This observation is consistent with previous reports on the molecular cut-off size for vascular extraction for this tumour cell line. The specific enhancement of tumour tissue suggest potential utility of NC100150 Injection as an angiogenesis marker.

A targeted contrast agent for magnetic resonance imaging of thrombus: implications of spatial resolution

A preparation of ultra-small superparamagnetic iron oxide (USPIO) particles coupled to an RGD peptide (RGD-USPIO) was investigated as an MR contrast agent, targeted to activated platelets, in both ex vivo and in vivo thrombus models. Thrombus visualization ex vivo was compared using RGD-USPIO and a non-targeted UPSIO. The influence of thrombus visualization on thrombus exposure time to RGD-USPIO (ex vivo) and on the spatial resolution of the MR image (ex vivo and in vivo) was assessed. RGD-USPIO resulted in better thrombus visualization than non-targeted USPIO ex vivo, and maximum enhancement was achieved after approximately one hour exposure time of the thrombus to RGD-USPIO. The ability to visualize the clots was highly dependent on the spatial resolution of the image. In vivo, an in-plane resolution of less than 0.2 x 0.2 mm(2) was required for good clot visualization after contrast enhancement. It is concluded that the achievable resolution and sensitivity is a potential limitation to the usefulness of active vascular targeting in MRI.

Thermosensitive paramagnetic liposomes for temperature control during MR imaging-guided hyperthermia: in vitro feasibility studies

RATIONALE AND OBJECTIVES

Magnetic resonance (MR) imaging-based temperature monitoring has gained interest for use in general hyperthermia treatment of tumors. Such therapy requires an accurate control of the temperature, which should range from 41 degrees to 45 degrees C. A novel type of thermosensitive MR agent is proposed: liposome-encapsulated gadolinium chelates whose temperature response is linked to the phase-transition properties of the liposome carrier. In vitro relaxometry and MR imaging were used to evaluate the thermosensitivity of the contrast properties of liposomal gadolinium diethylenetriaminepentaacetic acid bis(methylamide) (Gd-DTPA-BMA).

MATERIALS AND METHODS

T1 relaxivity (rl) measurements of liposomal Gd-DTPA-BMA were undertaken at 0.47 T and at temperatures of 20 degrees-48 degrees C. MR imaging was performed at 2.0 T with a gel phantom containing inserts of liposomes. Diffusion-weighted and T1-weighted gradient-recalled echo images were acquired as the phantom was heated from 22 degrees to about 65 degrees C.

RESULTS

At ambient temperature, the r1 of liposomal Gd-DTPA-BMA was exchange limited due to slow water exchange between the liposome interior and exterior. A sharp, marked increase in r1 occurred as the temperature reached and exceeded the gel-to-liquid crystalline phase-transition temperature (Tm) of the liposomes (42 degrees C). The relaxation enhancement was mainly attributable to the marked increase in transmembrane water permeability, yielding fast exchange conditions. There was good correlation between the relaxometric and imaging results; the signal intensity on T1-weighted gradient-recalled echo images increased markedly as the temperature approached Tm. The temperature sensitivity of the diffusion-weighted technique differed from that of the liposome-based T1-weighted approach, with an apparent water diffusion coefficient increasing linearly with temperature.

CONCLUSION

Since the transition from low to high signal intensity occurred in the temperature range of 38 degrees - 42 degrees C, the investigated paramagnetic liposomes have a potential role as "off-on" switches for temperature control during hyperthermia treatment.

Effect of NC100150 injection on the (1)H NMR linewidth of human whole blood ex vivo: dependency on blood oxygen tension

The linewidth of the (1)H NMR signal (7.05 T) of human whole blood titrated with a superparamagnetic contrast agent (NC100150 injection) was evaluated at different blood oxygen tensions. In deoxygenated blood and low contrast agent concentrations, NC100150 injection caused a decrease in linewidth. After reaching a minimum, the linewidth increased as the concentration of NC100150 injection increased. At the concentration corresponding to the minimum linewidth, the magnetization of the extracellular space containing the NC100150 injection was equal to that of the paramagnetic (deoxygenated hemoglobin) intracellular space. The minimum linewidth is therefore consistent with a complete elimination of the local microscopic susceptibility effect, the major cause of linebroadening. Additionally, phantom studies were performed at 1.5 T, confirming that the contrast enhancement of NC100150 injection in blood is dependent on oxygen tension. The data suggest that NC100150 injection may be useful in differentiating vessels with varying relative oxygen tensions.

NC100150 Injection, a preparation of optimized iron oxide nanoparticles for positive-contrast MR angiography

A preparation of monocrystalline iron oxide nanoparticles with an oxidized starch coating, currently in clinical trials (NC100150 Injection; CLARISCAN), was characterized by magnetization measurements, relaxometry, and photon correlation spectroscopy. By combining the results with a measure of iron content, one can obtain the size and magnetic attributes of the iron cores, including the relevant correlation times for outer sphere relaxation (tau(SO) and tau(D)), and information about the interaction of the organic coating with both core and solvent. The results are 6.43 nm for the iron oxide core diameter, a magnetic moment of 4.38x10(-17) erg/G, and a water-penetrable coating region of oxidized oligomeric starch fragments and entrained water molecules. The latter extends the hydrodynamic diameter to 11.9 nm and lowers the average diffusivity of solvent about 64% (which increases tau(D) accordingly). The nanoparticles show little size-polydispersity, evidenced by the lowest value of r(2)/r(1) at 20 MHz reported to date, an asset for magnetic resonance angiography.

NC100150-enhanced 3D-SPGR MR angiography of the common carotid artery in a pig vascular stenosis model. Quantification of stenosis and dose optimization

PURPOSE

NC100150 is a new type of ultra-small iron oxide (USPIO) blood pool agent. The aim of this study was to compare NC100150-enhanced MR angiography (MRA) to time-of-flight (TOF) MRA, phase-contrast (PC) MRA, and digital subtraction angiography (DSA) in experimental stenoses in pigs, and furthermore to determine the optimal dose of the contrast agent.

MATERIAL AND METHODS

An experimental stenosis of the right and left common carotid artery (CCA) was applied surgically in 6 Yorkshire pigs. DSA was performed as the gold standard, followed by 3D-TOF, 3D-PC, and NC100150-enhanced MRA.

RESULTS

Eleven stenoses of the CCA were successfully applied. The degree of the stenosis, determined by NC100150-enhanced MRA, did not differ significantly from DSA, whereas TOF and PC MRA underestimated it. The image quality of the NC100150-enhanced MRA was superior to both TOF and PC MRA. The optimal dose of NC100150 was 5-6 mg Fe/kg, since higher doses did not further increase signal-to-noise ratio or contrast-to-noise ratio. There was a linear relationship between blood relaxation rate and contrast dose.

CONCLUSION

NC100150-enhanced MRA has the potential for quantification of carotid stenoses and provides an alternative to DSA. The optimal dose of NC100150 was 5-6 mg Fe/kg.

CBF and CBV measurements by USPIO bolus tracking: reproducibility and comparison with Gd-based values

The authors measured cerebral blood flow (CBF) and cerebral blood volume (CBV) by bolus tracking of a novel ultrasmall superparamagnetic iron oxide (USPIO) contrast agent (NC100150) and compared absolute and relative perfusion measurements with those obtained by a standard gadolinium-based contrast agent. They found a linear correlation between the two methods. A dose of 0.4 mg Fe/kg body weight was found to produce a signal drop similar to that of a standard 0.2 mmol/kg gadodiamide injection using spin-echo echoplanar imaging (SE-EPI) at 1.0 T. The measurements showed a high degree of reproducibility of repeated absolute as well as relative CBF and CBV values, lending further hope to the possibility of using magnetic resonance bolus tracking for routine CBF and CBV measurements. Finally, the authors present their initial experience with high-resolution, non-EPI CBV maps obtained from steady-state levels of an intravascular superparamagnetic contrast agent.

Abdominal MR angiography performed using blood pool contrast agents: comparison of a new superparamagnetic iron oxide nanoparticle and a linear gadolinium polymer

OBJECTIVE

We evaluated and compared two different experimental blood pool contrast agents for abdominal MR angiography in an animal model.

MATERIALS AND METHODS

In seven pigs, coronal T1-weighted three-dimensional fast field-echo images were obtained on a conventional 1.5-T MR imaging system before and after i.v. injection of the ultrasmall superparamagnetic iron oxide agent FeO-BPA. In another seven pigs, MR angiograms were acquired using the gadolinium polymer WIN 22181. Enhanced images were obtained 5-210 min after injection of FeO-BPA and 1-120 min after injection of WIN 22181.

RESULTS

Both blood pool agents yielded detailed angiograms of the abdominal vascular tree when imaging lasted 2 min. In-plane running vessels were imaged without saturation effects and with equivalent maximum signal-to-noise ratios. Half the maximum signal-to-noise ratio was reached 150 min after injection of FeO-BPA, whereas this interval was approximately 70 min for the gadolinium polymer. Because of these different imaging half-life periods, the effective diagnostic window provided by FeO-BPA was six to eight times longer than that of WIN 22181. In the liver, the vascular T1 shortening and the parenchymal T2* effect of FeO-BPA complemented each other, resulting in an optimal contrast-to-noise ratio significantly higher than that achieved with WIN 22181. This "double-contrast effect" in the liver was especially helpful when obtaining detailed MR portograms.

CONCLUSION

The blood pool agents FeO-BPA and WIN 22181 can be used to produce high-quality abdominal MR angiograms on standard MR imaging equipment. The contrast-to-noise ratio of hepatic vessels is best on iron oxide-enhanced images because of a T1-T2* synergistic effect in the liver. The longer diagnostic window provided by FeO-BPA coupled with the option of in-plane imaging suggests the usefulness of FeO-BPA in future MR imaging-guided vascular interventions.

[Experimental evaluation of superparamagnetic iron oxide particles in pulmonary MR angiography]

PURPOSE

Initial experimental results of contrast-enhanced pulmonary MR angiography using the new superparamagnetic iron oxide blood pool agent FeO-BPA.

METHOD

Pulmonary MRA was performed in 7 domestic pigs using a cardiac-triggered coronal T1-weighted FFE-Sequence before and up to 90 minutes after contrast injection obtained on a 1.5 T magnet with a standard gradient equipment. A dose of 4 mg Fe/kg bodyweight was used for MRA. The images were qualitatively assessed and compared with X-ray i.v.-DSA.

RESULTS

The injection of FeO-BPA allows the acquisition of unsaturated in-plane images of the pulmonary vascular tree down to the first order subsegmental branches including vessel diameters of approximately 1.5 mm. In the normal non-occluded vasculature, no signal void is seen in the TE range of 2.8-5.5 ms secondary to exceeding susceptibility effects which are caused by the iron oxide accumulation. Even 90 minutes after injection of FeO-BPA, assessment of the pulmonary vasculature is still satisfactory.

CONCLUSIONS

In the animal experiment, the use of the blood pool agent FeO-BPA provides detailed pulmonary angiograms even on a magnet with a conventional gradient system. The major advantage is the comfortable diagnostic window of > 1.5 hours which also portends its utility for future MR-guided pulmonary interventions.

Contrast-enhanced magnetic resonance urography. First experimental results with a polymeric gadolinium bloodpool agent

RATIONALE AND OBJECTIVES

The authors investigated the feasibility of contrast-enhanced excretory magnetic resonance urography to visualize the nonobstructed urinary tract with a macromolecular gadolinium-based bloodpool agent.

METHODS

Excretory magnetic resonance imaging was performed in seven pigs using a T1-weighted three dimensional fast-field-echo sequence before and up to 120 minutes after administration of a gadolinium bloodpool prototype agent.

RESULTS

During the first 15 minutes after injection, the urographic effect was predominantly poor. Visualization of the entire urinary tract was excellent in four pigs and incomplete but satisfactory in three 105 minutes after injection. Furosemide application was tested in one case, which improved image quality effectively. Corresponding to the physiological excretion rate, signal measurements in the renal parenchyma revealed a gradual decrease of the initially distinct contrast enhancement.

CONCLUSIONS

T1-weighted contrast-enhanced magnetic resonance urography using a polymeric gadolinium bloodpool allows detailed visualization of the normal urinary tract, while information about the excretory function is obtained simultaneously. However, application of a diuretic seems to be essential to prevent lengthy examination duration.