Weighted Gradient Echo Sequences Research Articles

Coronary Vessel Wall Contrast Enhancement Imaging as a Potential Direct Marker of Coronary Involvement: Integration of Findings From CAD and SLE Patients

ObjectivesThis study investigated the feasibility of visual and quantitative assessment of coronary vessel wall contrast enhancement (CE) for detection of symptomatic atherosclerotic coronary artery disease (CAD) and subclinical coronary vasculitis in autoimmune inflammatory disease (systemic lupus erythematosus [SLE]), as well as the association with aortic stiffness, an established marker of risk. BackgroundCoronary CE by cardiac magnetic resonance (CMR) is a novel noninvasive approach to visualize gadolinium contrast uptake within the coronary artery vessel wall. MethodsA total of 75 subjects (CAD: n = 25; SLE: n = 27; control: n = 23) underwent CMR imaging using a 3-T clinical scanner. Coronary arteries were visualized by a T2-prepared steady state free precession technique. Coronary wall CE was visualized using inversion-recovery T1 weighted gradient echo sequence 40 min after administration of 0.2 mmol/kg gadobutrol. Proximal coronary segments were visually examined for distribution of CE and quantified for contrast-to-noise ratio (CNR) and total CE area. ResultsCoronary CE was prevalent in patients (93%, n = 42) with a diffuse pattern for SLE and a patchy/regional distribution in CAD patients. Compared with control subjects, CNR values and total CE area in patients with CAD and SLE were significantly higher (mean CNR: 3.9 ± 2.5 vs. 6.9 ± 2.5 vs. 6.8 ± 2.0, respectively; p < 0.001; total CE area: median 0.8 [interquartile range (IQR): 0.6 to 1.2] vs. 3.2 [IQR: 2.6 to 4.0] vs. 3.3 [IQR: 1.9 to 4.5], respectively; p < 0.001). Both measures were positively associated with aortic stiffness (CNR: r = 0.61, p < 0.01; total CE area: 0.36, p = 0.03), hypercholesterolemia (r = 0.68, p < 0.001; r = 0.61, p < 0.001) and hypertension (r = 0.40, p < 0.01; r = 0.32, p < 0.05). ConclusionsWe demonstrate that quantification of coronary CE by CNR and total CE area is feasible for detection of subclinical and clinical uptake of gadolinium within the coronary vessel wall. Coronary vessel wall CE may become an instrumental novel direct marker of vessel wall injury and remodeling in subpopulations at risk.

Evaluation of Iron Content in Human Cerebral Cavernous Malformation Using Quantitative Susceptibility Mapping

The aims of this study were to investigate and validate quantitative susceptibility mapping (QSM) for lesional iron quantification in cerebral cavernous malformations (CCMs). Magnetic resonance imaging studies were performed in phantoms and 16 patients on a 3-T scanner. Susceptibility weighted imaging, QSM, and R2* maps were reconstructed from in vivo data acquired with a 3-dimensional, multi-echo, and T2*-weighted gradient echo sequence. Magnetic susceptibility measurements were correlated to susceptibility weighted imaging and R2* results. In addition, iron concentrations from surgically excised CCM lesion specimens were determined using inductively coupled plasma mass spectrometry and correlated with QSM measurements. The QSM images demonstrated excellent image quality for depicting CCM lesions in both sporadic and familial cases. Susceptibility measurements revealed a positive linear correlation with R2* values (R(2) = 0.99 for total, R(2) = 0.69 for mean; P < 0.01). Quantitative susceptibility mapping values of known iron-rich brain regions matched closely with those of previous studies and in interobserver consistency. A strong correlation was found between QSM and the concentration of iron phantoms (0.925; P < 0.01), as well as between QSM and mass spectroscopy estimation of iron deposition (0.999 for total iron, 0.86 for iron concentration; P < 0.01) in 18 fragments of 4 excised human CCM lesion specimens. The ability of QSM to evaluate iron deposition in CCM lesions was illustrated via phantom, in vivo, and ex vivo validation studies. Quantitative susceptibility mapping may be a potential biomarker for monitoring CCM disease activity and response to treatments.

Texture analysis of ultrahigh field T2*‐weighted MR images of the brain: Application to Huntington's disease

To develop a framework for quantitative detection of between-group textural differences in ultrahigh field T2*-weighted MR images of the brain. MR images were acquired using a three-dimensional (3D) T2*-weighted gradient echo sequence on a 7 Tesla MRI system. The phase images were high-pass filtered to remove phase wraps. Thirteen textural features were computed for both the magnitude and phase images of a region of interest based on 3D Gray-Level Co-occurrence Matrix, and subsequently evaluated to detect between-group differences using a Mann-Whitney U-test. We applied the framework to study textural differences in subcortical structures between premanifest Huntington's disease (HD), manifest HD patients, and controls. In premanifest HD, four phase-based features showed a difference in the caudate nucleus. In manifest HD, 7 magnitude-based features showed a difference in the pallidum, 6 phase-based features in the caudate nucleus, and 10 phase-based features in the putamen. After multiple comparison correction, significant differences were shown in the putamen in manifest HD by two phase-based features (both adjusted P values=0.04). This study provides the first evidence of textural heterogeneity of subcortical structures in HD. Texture analysis of ultrahigh field T2*-weighted MR images can be useful for noninvasive monitoring of neurodegenerative diseases.

The value of T2*-weighted gradient-echo MRI for the diagnosis of cerebral venous sinus thrombosis

ObjectivesThe purpose of this study is to compare the various magnetic resonance imaging (MRI) sequences when they are used to visualize and evaluate cerebral venous thrombosis. MethodsEleven patients with cerebral venous thrombosis were retrospectively analyzed using computed tomography, MRI, magnetic resonance angiography (MRA), and conventional angiography. The MR sequence included T1-weighted spin echo (SE) imaging, obtained before and after administration of contrast medium, T2-weighted turbo spin echo (TSE), fluid-attenuated inversion recovery (FLAIR), T2*-weighted conventional gradient-echo (GRE), as well as three-dimensional (3D) venous time-of-flight MRA and conventional angiography. ResultsIn all of our patients, the venous sinus thromboses were most successfully detected during the T2*-weighted GRE sequence. The thrombosis was well visualized with the T1-weighted SE sequence in three of four patients in whom it was in the subacute stage. The T2*-weighted GRE sequence was superior to the T2-weighted TSE, T1-weighted SE, and FLAIR sequences in all patients. Enhanced 3D MR venography showed the thrombosed segment of the venous sinus and well correlated with the conventional angiographic findings. ConclusionsThe T2*-weighted conventional GRE sequences may be the best method for detecting of cerebral venous thrombosis. Therefore, it would seem to be beneficial to integrate a T2*-weighted conventional GRE sequence into the MR protocol to diagnose cerebral venous thrombosis.

Spin echo functional MRI in bilateral auditory cortices at 7 T: an application of B₁ shimming.

Ultra high fields (UHF) permit unprecedented explorations of functional organizations and insight into basic neuronal processes. Increases in the signal and contrast to noise ratios have allowed increases in the spatial resolution of T(2) weighted gradient echo (GE) echo planar imaging (EPI). Furthermore, while the use of T(2) weighted imaging methods at UHF (e.g. spin echo (SE) EPI, gradient and spin echo (GRASE) EPI) can also permit higher resolution images, they in addition allow for increased spatial specificity of functional responses, permitting the in-vivo study of functional organizations down to the columnar level of the cortex. The study of the visual cortex has, thus far, benefitted the most from higher resolution T(2) weighted studies as achieving the required transmit B(1) magnitude at 7T is more challenging in other brain regions, such as the auditory cortex. As such, auditory fMRI studies at UHF have been limited to T(2) weighted GE sequences. Recent advances in multi-channel RF transmission (e.g. B(1) shimming) have enabled procedures to efficiently address deficiencies in transmit B(1) profiles. However, these techniques, shown to be advantageous in anatomical imaging at UHF, are not generally utilized to facilitate T(2) weighted fMRI studies. Here we investigate the feasibility of applying B(1) shimming to achieve efficient RF transmission in the human auditory cortex. We demonstrate that, with B(1) shimming, functional responses to simple tones and to complex sounds (i.e. voices, speech, animal cries, tools and nature) can be efficiently measured with T(2) weighted SE-EPI in the bilateral human auditory cortex at 7T without exceeding specific absorption rate (SAR) limits.

7T Brain MR Imaging of Neurosarcoidosis: Preliminary Observations (S08.006)

Objective: To describe imaging characteristics of neurosarcoidosis on unenhanced 7T MRI. Background Non-caseating granulomatous inflammation in sarcoidosis is characterized by organized collections of mononuclear phagocytes, cells that are known to sequester microscopic quantities of calcium, iron and ferritin. We hypothesized that 7 tesla MR phase imaging, due to its high spatial resolution, sensitivity to these compounds, and ability to visualize tiny venous structures, would reveal novel features of neurosarcoidosis not currently visualized using 3T MRI. Design/Methods: Pilot study of 7T MRI in patients with neurosarcoidosis. Diagnosis was established by confirmatory biopsy of CNS tissue or extra-CNS tissue in patients with an otherwise typical neurological syndrome. Participants underwent imaging on a 7T GE scanner using a 2D T2*-weighted gradient echo sequence at 190 x 260 micron in-plane resolution (TR/TE=250/12 msec, 20 degree flip angle, 2 mm slice thickness, 3 signal averages). Magnitude and unwrapped phase images were generated from the raw image data using in-house software. Results: 7T MRI was performed in six patients with CNS sarcoidosis, 3 with definite disease and 3 with probable disease (the latter established by mediastinal/lung biopsy). All participants were on immunosuppressive therapy at time of imaging, and four had active disease at the time 7T MRI was performed. Three distinctive imaging features emerged: 1) several enhancing lesions at 3T were seen as T2* hypointense nodules on 7T images; 2) lesions seen on 3T T2-weighted sequences tended to spread across multiple veins in the white matter on 7T, rather than a single vein; 3) perimedullary veins on 7T sometimes appeared distorted in regions that corresponded to areas of meningeal and perivascular enhancement on 3T. These features differ in several respects from initial reports of 7T MRI of demyelinating plaques in MS. Conclusions: Active neurosarcoidosis lesions exhibit distinctive features on 7T MRI that may assist in noninvasive diagnosis. Supported by: American Academy of Neurology Clinical Research Training Fellowship (JMG). Disclosure: Dr. Gelfand has received personal compensation in an editorial capacity for Journal Watch Neurology. Dr. Green has received personal compensation for activities with Novartis and Biogen Idec as a consultant and/or participant on an advisory board and adjudication committee. Dr. Hess has nothing to disclose.

Seven‐tesla magnetic resonance images of the substantia nigra in Parkinson disease

To investigate anatomical changes in the substantia nigra (SN) of Parkinson disease (PD) patients with age-matched controls by using ultra-high field magnetic resonance imaging (MRI). We performed 7T MRI in 10 PD and 10 age-matched control subjects. Magnetic resonance images of the SN were obtained from a 3-dimensional (3D) T(2)*-weighted gradient echo sequence. Region of interest-based 3D shape analysis was performed to quantitatively compare images from the 2 groups. The boundary between the SN and crus cerebri was not smooth in PD subjects. Undulation in the lateral surface of the SN appeared more intense in the side contralateral to that with the more severe symptoms, and more prominent at the rostral level of the SN than at the intermediate or caudal levels. In addition to the lateral surface, there was a striking difference in the dorsomedial aspects of the SN between PD and control subjects. In control subjects, a brighter signal region was observed along the dorsomedial surface of the lateral portion of SN, whereas in PD subjects, this region was observed as a dark region containing a hypointense signal in T(2)*-weighted images. The measurement of SN volumes, normalized to the intracranial volumes, showed higher values in PD subjects than in control subjects. This study demonstrates that 3D 7T MRI can definitively visualize anatomical alterations occurring in the SN of PD subjects. Further pathological studies are required to elucidate the nature of these anatomical alterations.

Magnetic Resonance Imaging Compatibility of the Polymer-based Cochlear Implant

ObjectivesIn this study, we compared the magnetic resonance (MR) image artifacts caused by a conventional metal-based cochlear implant and a newly developed liquid crystal polymer (LCP)-based device.MethodsThe metal-based cochlear implant system (Nurobiosys Co.) was attached to side of the head of a subject and the LCP-based device was attached to opposite side. In both devices, alignment magnets were removed for safety. Magnetic resonance imaging (MRI) was performed on a widely used 3.0 T and an ultra-high 7.0 T MRI machine. 3.0 and 7.0 T MR images were acquired using T1- and T2*-weighted gradient echo sequences, respectively.ResultsIn the 3.0 T images, the metal-based device on the left side generated the significant amount of artifacts. The MR images in the proximity of the metal package were obscured by the artifacts in both axial and sagittal views. On the other hand, the MR images near the LCP-based device were relatively free from the artifacts and clearly showed the brain structures. 7.0 T MR images showed the more severe distortion in the both sides but the metal-based cochlear implant system caused a much larger obscure area than the LCP-based system.ConclusionThe novel LCP-based cochlear implant provides a good MRI compatibility beyond present-day cochlear implants. Thus, MR images can be obtained from the subjects even with the implanted LCP-based neural prosthetic systems providing useful diagnostic information. Furthermore, it will be also useful for functional MRI studies of the auditory perception mechanism after cochlear implantations as well as for positron emission tomography-MRI hybrid imaging.

Predictors and Early Outcome of Hemorrhagic Transformation after Acute Ischemic Stroke

Background: Hemorrhagic transformation (HT) after acute ischemic stroke is frequently detected using magnetic resonance imaging (MRI), in particular in patients treated with tissue plasminogen activator (tPA). Knowledge about causes and early clinical consequences of HT mostly arises from computed tomography-based studies. We analyzed potential predictors and early outcome of HT after stroke detected by MRI with T₂*-weighted gradient echo sequences (T₂*-MRI). Methods: 122 consecutive stroke patients (mean age 65.5 years, 41% women) who underwent T₂*-MRI within 6–60 h after stroke onset were included. 25.4% of patients were treated with tPA; the overall detection rate of HT on T₂*-MRI was 20.5%. Potential predictors of HT, such as age, sex, blood pressure, stroke etiology, prior antithrombotic medication, neurological deficit on admission, tPA treatment, and specific MRI findings, were analyzed. In addition, we evaluated the effect of HT on early outcome: a decrease of >4 points on the National Institute of Health Stroke Scale (NIHSS) on day 5 was considered early improvement, and an increase of >4 points was considered early deterioration. Results: The main predictor for occurrence of HT was tPA treatment (48.4 vs. 11.1%; odds ratio 7.50; 95% confidence interval 2.9–19.7; p < 0.001). Furthermore, the development of HT was associated with a severer neurological deficit on admission (mean NIHSS score 9.9 vs. 5.9; p = 0.003), and territorial infarction (88 vs. 58.8%; p = 0.007). 19 patients (15.6%) showed early improvement which was associated with the occurrence of HT (p = 0.011) and tPA treatment (p < 0.001). Conclusions: HT is a frequent finding on T₂*-MRI in patients with acute ischemic stroke associated with tPA treatment, territorial infarction and severer neurological deficits on admission. However, HT does not cause clinical deterioration; it is rather related to a favorable early outcome likely reflecting early recanalization and better reperfusion in these patients.

An magnetic resonance imaging T2*‐weighted sequence at short echo time to detect putaminal hypointensity in Parkinsonisms

At 1.5 T, T2*-weighted gradient echo (GE) sequences are more sensitive in revealing mineral deposition in the basal ganglia than standard T2 weighted sequences. T2*-weighted GE sequences, however, may detect putaminal hypointensities either in patients affected by parkinsonian syndromes or in healthy subjects. The aim of this study was to identify the magnetic resonance imaging (MRI) T2*-weighted sequence which more specifically detected putaminal hypointensities differentiating atypical parkinsonian syndromes from Parkinson's disease (PD) and control subjects. In a sample of 38 healthy subjects, we performed three T2*-weighted GE sequences at increasing time echo (TE; TE = 15 millisecond, TE = 25 millisecond, and echoplanar at TE = 40 millisecond; T2* sequences study). The sequence not showing any putaminal abnormality in the healthy subjects was then used to assess putaminal signal intensity in 189 patients with PD, 20 patients with multiple system atrophy (MSA), 41 patients with progressive supranuclear palsy (PSP), and in 150 age and sex-matched control subjects. In the T2* sequences study, the T2*-weighted TE = 15 (T2*/15) did not show any putaminal abnormalities in the healthy subjects. This sequence detected putaminal hypointensities in a significantly higher proportion of patients with MSA (35%, P < 0.05) and PSP (24.4%, P < 0.05) than in patients with PD (5.3%), but in none of the controls. The sensitivity of putaminal hypointensity in T2*/15 sequence was 25.4% for PD, 43.9% for PSP, and 55% for MSA versus controls whereas the specificity was 93.2% for all groups. Despite the suboptimal sensitivity, the high specificity of the T2*/15 sequence performed on routine MRI suggests its usefulness in clinical practice for identifying putaminal hypointensities associated with parkinsonian disorders.

Spontaneous recovery from progressive multifocal leukoencephalopathy in a patient with non-active sarcoidosis

We report the case of a 50-year-old female patient with non-active sarcoidosis and no kind of immunosuppression, admitted to our hospital because of increasing confusion and focal neurological deficits. Initially a tumor, herpes encephalitis, or neurosarcoidosis were suspected, but surprisingly biopsy revealed progressive multifocal leukoencephalopathy, additionally confirmed by JC-positive PCR in cerebrospinal fluid. Cases of sarcoidosis and progressive multifocal leukoencephalopathy have been reported before. This is the first case of a patient with no sign of active sarcoidosis and without immunosuppressive therapy who recovered spontaneously with a follow-up time of nearly 3 years.

Cerebral Cavernous Hemangiomas at 7 Tesla: Initial Experience

Cavernous malformations (cavernomas) occur in 0.4%-0.9% of the population. The most common symptoms of cavernous malformations are seizures. An improved detection of small cavernomas might possibly help to clarify cryptogenic seizures, which represent 30% of all seizures. The aim of this study was to evaluate the benefit of magnetic resonance imaging at a field strength of 7 T in the detection of cavernomas. Ten consecutive patients with known cavernomas were enrolled in this study. First a T2*-weighted gradient echo sequence was performed at 1.5 T with a slice thickness of 6 mm in axial orientation. Subsequently, the examination was repeated at 7 T. Both examinations were independently read by two blinded senior neuroradiologists. Localization and dimension of the hypointensities were recorded. One additional hypointensity was detected in one patient, which was not visible in the 1.5 T examination even retrospectively. In another patient with known cavernomatosis, innumerable new small hypointense lesions were detected at 7 T. Our small series suggests that ultra-high-field magnetic resonance imaging at 7 T improves the detection of cavernomas.

Use of standing low‐field magnetic resonance imaging to diagnose middle phalanx bone marrow lesions in horses

SummaryBone marrow lesions (BMLs) (also known as ‘bone bruises’, ‘bone oedema’, ‘bone contusions’ and ‘occult fractures’) within the middle phalanx were diagnosed by standing low field magnetic resonance imaging (MRI) in 7 horses. The lesions were characterised by low signal intensity on T1‐ and T2*‐weighted gradient echo sequences, mildly increased signal intensity on T2 fast spin echo sequences, and high signal intensity on short tau inversion recovery (STIR) sequences. Four distinct patterns of abnormal signal were identified: BML associated with osteoarthritis of either the proximal or distal interphalangeal joints; BML associated with soft tissue injury; BML associated with acute trauma; and BML unassociated with any other injury or lameness (assumed to represent bone response to biomechanical stress). Repeat MRI was undertaken in 4 cases. In most cases the BML resolved with rest and time, although lameness was persistent in 2 horses (one of which had an associated osteoarthritis of the proximal interphalangeal joint).

Steroid-responsive edema in CAA-related inflammation

JO N 3136 An 80-year old woman was admitted with sudden right-sided hemiparesis, dysphasia and altered mental status. There was no preceding infection or vaccination. She had an epileptic seizure after which we started phenytoin. Vital signs were BP 130/70, pulse 87, temperature 37.1 °C. MRI revealed white matter abnormalities, exerting a slight mass effect (Fig. 1 A). No gadolinium enhancement was observed. Serum and cerebrospinal fluid studies were within normal limits. After exclusion of infection we started dexamethasone 4 mg/ day and observed a clear recovery. The initial follow-up MRI was comparable with the previous MRI. Diffusion weighted images suggested that the white matter abnormalities represented vasogenic edema (Fig. 1 D). A T2*-weighted gradient echo sequence revealed multiple petechial hemorrhages or cerebral microbleeds (CMB, Fig. 1 B). In the absence of the classical vascular risk factors, we diagnosed CAA and continued dexamethasone in a gradually tapering scheme. The patient recovered, but relapsed after two months. She responded well to a temporary increase of dexamethasone. Four months later we could stop the dexamethasone. She had a mild residual dysphasia with a full recovery of cognition. Repeated MRI showed a clear reduction in brain edema (Fig. 1 C). Following the Boston criteria [3], we classified our patient as ‘probable CAA’. Post-mortem neuropathological examination is still considered the most reliable tool for diagnosing CAA. CAA can be identified in vivo by histological analyses upon evacuating a hematoma or by cortical biopsy. Because our patient responded well to steroid treatment, we did not perform a brain biopsy. The need for biopsy in the diagnosis of CAA is likely to decrease in the future, since KnudRichard Daniels Jeroen J. G. Geurts Joost C. Bot Wouter J. Schonewille Bob W. van Oosten

First Clinical Study on Ultra-High-Field MR Imaging in Patients with Multiple Sclerosis: Comparison of 1.5T and 7T

Higher magnetic field strengths and continuous improvement of high-resolution imaging in multiple sclerosis (MS) are expected to provide unique in-vivo and non-invasive insights in pathogenesis and clinical monitoring. The purpose of this study was to investigate the potential of high-resolution imaging of MS lesions in vivo comparing 7T with conventional 1.5T. Twelve consecutive patients with clinically definite MS were scanned on a 7T whole-body scanner and on a 1.5T Avanto. The 1.5T and 7T imaging protocol consisted of high-resolution axial proton density (PD) + T2-weighted turbo spin-echo and T2*-weighted gradient-echo (GRE), and sagittal T1-weighted 3D magnetization-prepared rapid acquisition of gradient echo. The sequence parameters at 7T had to be modified because of specific absorption rate (SAR) restrictions while keeping contrast parameters equivalent to 1.5T. White matter lesions were better detected and delineated from adjacent structures at 7T compared with 1.5T. There were 42% of the patients who showed additional lesions at 7T: there were 97 white matter lesions detected on 1.5T versus 126 lesions at 7T, an increase of 23%. The perivascular migration of MS lesions was well visualized on T2*-weighted GRE sequences. In larger lesions (10 mm), a multilayer structure was revealed on T2*-weighted GRE not seen at 1.5T. Because of the higher resolution, it was possible to differentiate between juxtacortical white matter lesions and cortical lesions. There were 44% of the subcortical lesions depicted at 7T that showed cortical involvement. Ultra-high-field imaging of patients with MS at 7T was well tolerated and provided better visualization of MS lesions in the gray matter and demonstrated structural abnormalities within the MS lesions themselves more effectively.

Detection of Hepatocellular Carcinoma with Ferucarbotran (Resovist)-enhanced Breath-hold MR Imaging: Feasibility of 10 minute-delayed Images

We evaluated the optimal timing for breath-hold MR imaging with bolus-injectable superparamagnetic iron oxide (SPIO) for detecting hepatocellular carcinoma (HCC). Twenty patients with 62 HCCs (52 hypervascular, 10 non-hypervascular) underwent MR imaging that included unenhanced and SPIO-enhanced T1-weighted gradient echo (GRE) and T2-weighted fast spin echo (FSE) sequences, perfusion study, and SPIO-enhanced T2*-weighted GRE sequences. We obtained SPIO-enhanced T2*-weighted sequences 10 and 30 min after injecting SPIO and made 2 image sets, comprising 10- or 30-min delayed T2*-weighted images. Three observers performed alternative free response receiver operating characteristic (AFROC) analysis, and quantitative evaluation was performed. Only Observers 2 and 3 recognized a significant difference in the area under the AFROC curve (Az) value in the 10-min delayed images; no significant difference was observed in the 30-min delayed images. There was no significant difference in the sensitivity of individual observers between 10- and 30-min delayed images. The contrast-to-noise (C/N) ratio of the 30-min delayed images was significantly higher than that of the 10-min delayed images. The C/N ratio of hypervascular HCCs in the 30-min delayed images was significantly higher than in the 10-min delayed images, but that of non-hypervascular HCCs showed no significant difference. In most cases, 10-min delayed SPIO-enhanced T2*-weighted images are sufficient to detect HCCs.

Usefulness of Combining Sequentially Acquired Gadobenate Dimeglumine-Enhanced Magnetic Resonance Imaging and Resovist-Enhanced Magnetic Resonance Imaging for the Detection of Hepatocellular Carcinoma

To investigate the diagnostic efficacy of sequentially acquired gadobenete dimeglumine-enhanced 3-dimensional dynamic magnetic resonance imaging (MRI) and Resovist-enhanced MRI for detecting hepatocellular carcinoma (HCC) by comparing with combined computed tomography (CT) hepatic arteriography (CTHA) and CT arterioportography (CTAP) using 16-slice multidetector CT. Twenty-nine patients with 50 HCCs underwent sequentially acquired double-contrast MRI--gadobenate dimeglumine-enhanced dynamic MRI and Resovist-enhanced MRI--and combined CTHA and CTAP using 16-slice multidetector CT. Dynamic MRI was obtained using volumetric interpolated technique and sensitivity encoding on a 1.5-T unit. Resovist-enhanced MRI was composed of T2-weighted turbo spin-echo and T2*-weighted gradient echo sequences. Sensitivity, positive predictive value, and diagnostic accuracy for double-contrast MRI, gadolinium-enhanced MRI, and combined CTHA and CTAP were calculated by 2 observers using an alternative-free response receiver operating characteristic analysis. For all observers, the Az values of double-contrast MRI (mean, 0.96) and combined CTHA and CTAP (mean, 0.93) were similar, which tended to be better than that of gadolinium-enhanced MRI (mean, 0.91). The sensitivity of double-contrast MRI (mean, 93%) and combined CTHA and CTAP (mean, 92%) was equivalent for all observers, which was better than that of gadolinium-enhanced MRI (mean, 85%; P < 0.05). The positive predictive value of double-contrast MRI was better than that of combined CTHA and CTAP (P < 0.05). The sequentially acquired double-contrast MRI and combined CTHA and CTAP showed a similar diagnostic accuracy and sensitivity for detecting HCC.

Evaluation of small (≤2 cm) dysplastic nodules and well-differentiated hepatocellular carcinomas with ferucarbotran-enhanced MRI in a 1.0-T MRI unit: Utility of T2*-weighted gradient echo sequences with an intermediate-echo time

Purpose To evaluate the detectability and signal intensities of small (≤2 cm) dysplastic nodules (DNs) and well-differentiated hepatocellular carcinomas (w-HCCs) by T2*-weighted gradient echo (GRE) sequences using an intermediate echo-time (TE) with ferucarbotran in a 1.0-T magnetic resonance imaging (MRI) unit. Materials and methods Pathologically confirmed DNs ( n = 13) and w-HCCs ( n = 31) with a median largest dimension of 1.1 cm were scanned using ferucarbotran-enhanced MRI. Conventional T2*-weighted GRE sequences (conventional-T2*-GRE: repetition time, 280 ms; echo time, 14 ms; flip angle, 60°) and specific T2*-weighted GRE sequences using an intermediate-TE (specific-T2*-GRE: repetition time, 140 ms; echo time, 8 ms; flip angle, 30°) were obtained before and after ferucarbotran administration. Two independent observers scored all nodules for visibility and assigned confidence level scores to their observations. To assess the effect of ferucarbotran, the tumor-liver signal contrast-to-noise ratio (tumor-liver-CNR) was also calculated for detected nodules by the same two observers with consensus. Results There was good interobserver agreement regarding the presence of nodules for both sequence types. Qualitative and quantitative analyses indicated that specific-T2*GRE sequences were superior to conventional-T2*-GRE sequences for detecting DNs and w-HCCs with hypointense signals. The tumor-liver-CNR of DNs was significantly different between specific-T2*-GRE sequences and conventional-T2*-GRE sequences (Mann–Whitney test, P < 0.001). Both qualitative and quantitative analyses indicated that conventional-T2*-GRE sequences were superior to specific-T2*-GRE sequences for detecting w-HCCs with heterogeneous and hyperintense signals. Conclusion Specific-T2*-GRE sequences with ferucarbotran are useful for detecting DNs and w-HCCs that produce hypointense signals on a 1.0-T MRI unit.

T2*-weighted MRI in diagnosis of multiple system atrophy

Putaminal iron deposition is a histopathological feature of multiple system atrophy (MSA), which is not observed in patients with idiopathic Parkinson's disease (PD). T2*-weighted magnetic resonance imaging (MRI) gradient echo (GE) sequences are sensitive for paramagnetic susceptibility changes and therefore may support the clinical differential diagnosis between MSA and PD. We evaluated putaminal signal intensities on 1.0 Tesla scans of 52 MSA patients, 88 patients with PD and 29 healthy control subjects. The typical finding in T2* GE sequences of MSA patients was a signal loss of the dorsolateral putamen, which showed a high specificity (>0.91), but was present in only a subpopulation of patients (sensitivity 0.64-0.69). The combination of the latter with additional presence of a hyperintense lateral rim in fluid attenuated inversion recovery (FLAIR) sequences increased the specificity to 0.97. Using a quantitative evaluation of putaminal signal intensities in defined regions of interest MSA and PD could be discriminated with a diagnostic accuracy (r) of up to 0.82. Although the separation of groups remains incomplete, the use of T2*-weighted GE sequences combined with FLAIR may be helpful for the differential diagnosis of MSA versus PD considering its fast application, easy evaluation, broad availability, the specificity of findings and the presence of putaminal signal loss already at early disease stages.

Susceptibility Weighted Imaging: Data Acquisition, Image Reconstruction and Clinical Applications

Susceptibility-weighted imaging (SWI) is a novel method, that combines magnitude and phase information from a high-resolution, fully velocity compensated 3D T2*-weighted gradient echo sequence. Phase images are unwrapped and high pass filtered to highlight phase changes associated with venous vessels and converted into a mask that is multiplied with the corresponding phase image. This technique has been applied thus far to the imaging of tumors, vascular malformations, trauma, stroke, micro-hemorrhages, and as a functional imaging method. The purpose of this paper is to present an overview of the current status of the technique and to illustrate its potential.