FLAIR MRI biomarkers of the normal appearing brain matter are related to cognition.

A novel biomarker panel was proposed to quantify macro and microstructural biomarkers from the normal-appearing brain matter (NABM) in multicentre fluid-attenuation inversion recovery (FLAIR) MRI. The NABM is composed of the white and gray matter regions of the brain, with the lesions and cerebrospinal fluid removed. The primary hypothesis was that NABM biomarkers from FLAIR MRI are related to cognitive outcome as determined by MoCA score. There were three groups of features designed for this task based on 1) texture: microstructural integrity (MII), macrostructural damage (MAD), microstructural damage (MID), 2) intensity: median, skewness, kurtosis and 3) volume: NABM to ICV volume ratio. Biomarkers were extracted from over 1400 imaging volumes from more than 87 centres and unadjusted ANOVA analysis revealed significant differences in means of the MII, MAD, and NABM volume biomarkers across all cognitive groups. In an adjusted ANCOVA model, a significant relationship between MoCA categories was found that was dependent on subject age for MII, MAD, intensity, kurtosis and NABM volume biomarkers. These results demonstrate that structural brain changes in the NABM are related to cognitive outcome (with different relationships depending on the age of the subjects). Therefore these biomarkers have high potential for clinical translation. As a secondary hypothesis, we investigated whether texture features from FLAIR MRI can quantify microstructural changes related to how "structured" or "damaged" the tissue is. Based on correlation analysis with diffusion weighted MRI (dMRI), it was shown that FLAIR MRI texture biomarkers (MII and MAD) had strong correlations to mean diffusivity (MD) which is related to tissue degeneration in the GM and WM regions. As FLAIR MRI is routinely collected for clinical neurological examinations, novel biomarkers from FLAIR MRI could be used to supplement current clinical biomarkers and for monitoring disease progression. Biomarkers could also be used to stratify patients into homogeneous disease subgroups for clinical trials, or to learn more about mechanistic development of dementia disease.

Roadmap Consensus on Carotid Artery Plaque Imaging and Impact on Therapy Strategies and Guidelines: An International, Multispecialty, Expert Review and Position Statement.

Current guidelines for primary and secondary prevention of stroke in patients with carotid atherosclerosis are based on the quantification of the degree of stenosis and symptom status. Recent publications have demonstrated that plaque morphology and composition, independent of the degree of stenosis, are important in the risk stratification of carotid atherosclerotic disease. This finding raises the question as to whether current guidelines are adequate or if they should be updated with new evidence, including imaging for plaque phenotyping, risk stratification, and clinical decision-making in addition to the degree of stenosis. To further this discussion, this roadmap consensus article defines the limits of luminal imaging and highlights the current evidence supporting the role of plaque imaging. Furthermore, we identify gaps in current knowledge and suggest steps to generate high-quality evidence, to add relevant information to guidelines currently based on the quantification of stenosis.

Pathology-preserving intensity standardization framework for multi-institutional FLAIR MRI datasets.

Fluid-Attenuated Inversion Recovery (FLAIR) MRI are used by physicians to analyze white matter lesions (WML) of the brain, which are related to neurodegenerative diseases such as dementia and vascular disease. To study the causes and progression of these diseases, multi-centre (MC) studies are conducted, with images acquired and analyzed from multiple institutions. Due to differences in acquisition software and hardware, there is variability in image properties, which creates challenges for automated algorithms. This work explores this variability, known as the MC effect, by analyzing nearly 5000 MC FLAIR volumes and proposes an intensity standardization framework to normalize intensity non-standardness in FLAIR MRI, while ensuring the appearance of WML. Results show that original image characteristics varied significantly between scanner vendors and centres, and that this variability was reduced with standardization. To further highlight the utility of intensity standardization, a threshold-based brain extraction algorithm is implemented and compared with a classifier-based approach. A competitive Dice Similarity Coefficient of 81% was achieved on 183 volumes, demonstrating that optimized pre-processing can effectively reduce the variability in MC studies, allowing for simplified algorithms to be applied on large datasets robustly.

Carotid Artery Wall Imaging: Perspective and Guidelines from the ASNR Vessel Wall Imaging Study Group and Expert Consensus Recommendations of the American Society of Neuroradiology.

Identification of carotid artery atherosclerosis is conventionally based on measurements of luminal stenosis and surface irregularities using in vivo imaging techniques including sonography, CT and MR angiography, and digital subtraction angiography. However, histopathologic studies demonstrate considerable differences between plaques with identical degrees of stenosis and indicate that certain plaque features are associated with increased risk for ischemic events. The ability to look beyond the lumen using highly developed vessel wall imaging methods to identify plaque vulnerable to disruption has prompted an active debate as to whether a paradigm shift is needed to move away from relying on measurements of luminal stenosis for gauging the risk of ischemic injury. Further evaluation in randomized clinical trials will help to better define the exact role of plaque imaging in clinical decision-making. However, current carotid vessel wall imaging techniques can be informative. The goal of this article is to present the perspective of the ASNR Vessel Wall Imaging Study Group as it relates to the current status of arterial wall imaging in carotid artery disease.

Magnetic resonance direct thrombus imaging.

As blood clots it goes through predictable stages that reflect the oxygenation state of hemoglobin within the red cells. One of these stages results in the formation of methemoglobin. This substance acts an endogenous contrast agent when imaged using a T1-weighted magnetic resonance sequence (Magnetic Resonance Direct Thrombus Imaging, MRDTI) - appearing as high signal. MRDTI can therefore be used to detect subacute thrombosis. This technique has been applied in a number of clinical settings arising as a result of thrombosis. Deep vein thrombosis and pulmonary embolism are both readily detected using MRDTI, providing a single imaging modality for the detection of venous thromboembolic disease. The technique is also effective in the peripheral arterial tree. Furthermore, thrombosis within vessel wall atherosclerosis is a marker of vulnerable plaque likely to produce symptoms. The MRDTI technique has thus proved useful in identifying complicated plaque in the carotid arteries in the setting of transient and permanent cerebral ischemia. MRDTI therefore holds promise as a technique that is capable of detecting high risk vessel wall disease prior to significant or permanent end organ damage. Because of the non-invasive nature of magnetic resonance imaging (MRI), application of MRDTI in the research setting for the monitoring of therapeutic interventions in a wide number of settings within vascular disease is very appealing.

Magnetic resonance pulmonary angiography and direct imaging of embolus for the detection of pulmonary emboli.

RATIONALE AND OBJECTIVES: The authors developed a two-dimensional breathhold magnetic resonance (MR) technique for the direct imaging of pulmonary emboli. METHODS: In vitro MR imaging was performed to demonstrate the potential generation of clot-blood contrast by in vivo pulmonary embolism (PE). A two-dimensional magnetization prepared gradient-echo (turbo-FLASH) breathhold technique was designed to directly image intravascular emboli by the selective nulling of the blood signal. A turbo-FLASH pulmonary angiographic breathhold sequence was used to provide spatial localization of detected emboli. Thirteen patients with suspected PE were studied; 6 patients underwent conventional pulmonary angiography (CPA) and the remaining 7 had diagnoses based on findings from other studies. RESULTS: In vitro study of blood clot demonstrated an initial rise and then fall in T1 sufficient to generate clot-blood contrast after eight days of clot formation. All patients with CPA or alternative study evidence of PE were diagnosed as positive with direct embolus imaging MR. There were no false-positive diagnoses. Three additional emboli were detected using the MR technique compared with CPA. The MR pulmonary angiographic sequence provided a useful road map for localization of intravascular emboli but was less sensitive for PE detection than the embolus imaging technique. CONCLUSIONS: The direct imaging of PE is feasible using a simple two-dimensional breathhold technique.

Optimization of a breath-hold magnetic resonance gradient echo technique for the detection of interstitial lung disease.

RATIONALE AND OBJECTIVES: A rapid gradient echo technique was optimized to allow breath-held imaging of the lung parenchyma. The ability of this sequence to detect interstitial lung disease was then compared with high resolution computed tomography. METHODS: A Turbo-FLASH gradient echo sequence (repetition time [TR] 4.7, echo time [TE]2) was optimized using four volunteers. The parameters varied, including flip angle, inversion time, slice thickness, and number of measurements per unit time. The effect on signal to noise ratio of lung inflation and position within the lung were also studied. The optimized sequence was then compared with high resolution computed tomography in five patients being investigated for interstitial lung disease. RESULTS: Greatest signal was achieved using no inversion prepulse. This allowed up to six measurements, each with two acquisitions, during a single breath-hold. Optimum signal to noise ratio was achieved using a flip angle of 10 degrees with a 20-mm slice thickness, although a 10-mm slice was felt to be preferable for clinical use. Greatest signal to noise ratio was generated in the posterior aspect of the lung in full expiration. Comparison of the optimized magnetic resonance imaging technique with high resolution computed tomography showed no significant difference (P = 0.17) when assessing the proportion of diseased to normal lung. CONCLUSIONS: Using standard magnetic resonance software and hardware, it has been possible to use a breath-hold sequence that allows detection and quantification of interstitial lung disease.

Contrast-reduced imaging of tissue concentration and arterial level (CRITICAL) for assessment of cerebral hemodynamics in acute stroke by magnetic resonance.

RATIONALE AND OBJECTIVES: To compare cerebral perfusion data obtained by using a low-dose, T1-weighted MRI technique with radionuclide (single positron emission computed tomography [SPECT]) brain imaging and to assess the reproducibility of parametric MRI data (cerebral blood flow [CBF], cerebral blood volume [CBV], and time to peak [TTP]) by applying a previously described nuclear medicine technique to derive quantitative perfusion data. METHODS: Single-slice brain and neck images were rapidly acquired during the passage of a small (1/10th of normal dose) bolus of contrast. Parametric images were constructed from the MR data by extracting the bolus transit curve for the brain and the peak arterial input curve from the carotid vessels in the neck. These were compared with SPECT perfusion imaging. Twenty-four patients with acute stroke were studied with both techniques; 13 underwent repeated scanning to assess data reproducibility. RESULTS: Relative CBF data were comparable to SPECT data (r = 0.584, P = 0.01). Results were reproducible for relative CBF, CBV, and TTP. The arterial input function was significantly different on the second injection with an average difference of 73.5, suggesting that the signal-concentration relationship had lost linearity with increased contrast load. Absolute quantitative MRI data produced values in the expected range (CBF = 42.6 mL x 100 g(-1) x min(-1)). CONCLUSIONS: This technique allows estimation of CBF in the setting of acute stroke with quantitative values in the expected range. Repeated measurements in the same patients showed that this technique provides a reproducible measure of relative CBF, CBV, and TTP.

Dynamic T1 measurement using snapshot-FLASH MRI.

The application of an inversion-recovery snapshot FLASH (fast low-angled shot) imaging sequence to the dynamic measurement of monoexponential T1 relaxation was investigated. The effect of (a) a reduction in the overall sequence repetition time, and (b) an increase of the read-pulse flip angle, on the measurement of T1 was analyzed. The error in T1 introduced by these factors is calculated, and a fuller analysis that takes them into account is presented. Data from a phantom are used to confirm this analysis. The magnitude of the errors is illustrated by measuring myocardial T1 in patients with acute ischaemic heart disease during the injection of a bolus of the contrast medium gadobenate dimeglumine. Overall, there was a 10% difference between the T1 values when the approximate and exact solutions were used; this was statistically significant. However, the difference was on average 25% for patients with a high heart rate (because of the shorter sequence-repetition time) in areas of infarcted myocardium (because of the longer T1).

Extracting parametric images from dynamic contrast-enhanced MRI studies of the brain using factor analysis.

Factor analysis of dynamic studies (FADS) is a technique that allows structures with different temporal characteristics to be extracted from dynamic contrast enhanced studies without making any a priori assumptions about physiology. These dynamic structures may correspond to different tissue types or different organs or they may simply be a useful way of characterising the data. This paper describes a method of automatically extracting factor images and curves from contrast enhanced MRI studies of the brain. This method has been applied to 107 studies carried out on patients with acute stroke. The results show that FADS is able to extract factor curves correlated to arterial and venous signal intensity curves and that the corresponding factor images allow a distinction to be made between areas of the brain with normal and abnormal perfusion. The method is robust and can be applied routinely to dynamic studies of the brain. The constraints described are sufficiently general to be applicable to other dynamic MRI contrast enhanced studies where an increase in contrast concentration produces an increase in signal intensity.

Digital sialography: imaging and intervention.

Digital subtraction imaging (DSI) has been widely used in angiography but less commonly applied to sialography. Over a 3-year period 109 patients referred for sialography, 42 males and 67 females with a mean age of 44 years (range 8-85 years), were examined using a digital subtraction imaging technique. 13 patients went on to have an interventional procedure, stone removal or duct dilatation. The role of DSI imaging in sialography and its use in facilitating interventional procedures on the salivary glands are discussed.

Carotid atherosclerotic calcification does not result in high signal intensity in MR imaging of intraplaque hemorrhage.

BACKGROUND AND PURPOSE: Calcium can potentially shorten T1, generating high signal intensity in GREs. Because IPH appears as high signal intensity in MRIPH and the surface effects of calcium can potentially shorten T1 of surrounding water protons, the purpose of this study was to evaluate whether the high signal intensity seen on MRIPH could be attributed solely to IPH and not calcification. MATERIALS AND METHODS: Eleven patients undergoing carotid endarterectomy were imaged by using MRIPH. Calcification was assessed by scanning respective endarterectomy specimens with a tabletop MicroCT. MRIPH/MicroCT correlation used an 8-segment template. Two readers evaluated images from both modalities. Agreement between MRIPH/MicroCT was measured by calculating Cohen κ. RESULTS: High signal intensity was seen in 58.8% and 68.9% (readers 1 and 2, respectively) of MRIPH segments, whereas calcification was seen in 44.7% and 32.1% (readers 1 and 2, respectively) of MicroCT segments. High signal intensity seen by MRIPH showed very good but inverse agreement to calcification (κ = -0.90; P < .0001, 95% CI, -0.93 to -0.86, reader 1; and κ = -0.74; P < .0001; 95% CI, -0.81 to -0.69, reader 2). Most interesting, high signal intensity demonstrated excellent agreement with lack of calcification on MicroCT (κ = 0.92; P < .0001; 95% CI, 0.89-0.94, reader 1; and κ = 0.97; P < .0001; 95% CI, 0.96-0.99, reader 2). In a very small number of segments, high signal intensity was seen in MRIPH, and calcification was seen on MicroCT; however, these represented a very small proportion of segments with high signal intensity (5.9% and 1.6%, readers 1 and 2, respectively). CONCLUSIONS: High signal intensity, therefore, reliably identified IPH, known to describe complicated plaque, rather than calcification, which is increasingly recognized as identifying more stable vascular disease.

Gastroepiploic veins: CT appearance in pancreatic disease.

The frequency with which gastroepiploic vein (GEV) enlargement was seen on CT and its relevance to disease of the portal venous system associated with pancreatic disease were studied. We performed a retrospective study of 50 patients with proved pancreatic disease and another 50 patients without such disease. The CT examinations were done in incremental dynamic fashion after a bolus injection of contrast medium. Scans were evaluated for collateral channel formation, including GEV enlargement, and for involvement of the portal venous system by pancreatic disease. Part of the GEV arcade was visible in 36 patients without pancreatic disease, and on average measured 3.2 mm in diameter (range, 1-5.5 mm). GEV enlargement was visible in 62% of the patients with disease; 16% demonstrated a vessel 6 mm or more in diameter. Thirty-four percent of the patients with disease had portal venous complications: 26% had isolated splenic vein involvement, 2% had isolated portal vein involvement, and 6% had a combination of splenic and portal vein involvement. Of the patients with splenic vein disease, 81% had collateral channel formation, 50% of them demonstrating isolated GEV enlargement. Patients with splenic vein disease due to acute pancreatic disease had a much higher instance of GEV enlargement (83.3%). Collateral vessels are commonly seen on CT scans of patients with splenic vein disease and most often occur via enlarged GEVs. Acute pancreatic disease is frequently associated with GEV enlargement, suggesting that the latter represents an early response to splenic vein disease. In contrast, multiple collateral pathways tend to develop in patients with chronic pancreatic disease.

Atypical hepatic hemangioma: a suggestive sonographic morphology.

A retrospective review of the sonographic appearances of 29 proved atypical hemangiomas in 29 patients and a prospective study of the predictive capacity of these features were performed. The main confirmatory imaging examinations were computed tomography and technetium-labeled red blood cell radioisotope scanning with single photon emission computed tomography. The retrospective review showed that all tumors were solid. Twenty-seven tumors had an echogenic border, seen as a thick echogenic rind (n = 15) and a thin rim (n = 12). Unlike typical hemangiomas, which have a uniformly increased echogenicity relative to normal liver, all 29 tumors had an internal echo pattern that was at least partially hypoechoic. These morphologic criteria (a solid tumor with an echogenic border and partially hypoechoic internal pattern) were then prospectively applied to all hepatic tumors detected with sonography during a 6-month period. Fifteen lesions with these features were identified from among more than 5,000 abdominal scans. Twelve of these lesions were confirmed as, and two were presumed to be, cavernous hemangiomas; in one lesion, the diagnosis was false-positive. Recognition of these atypical features should increase suspicion of the presence of hemangiomas on sonograms.

Anomalous inferior vena cava demonstrated by contrast-enhanced magnetic resonance venography.

We discuss the technique of contrast-enhanced magnetic resonance venography and its advantages over other methods of imaging the veins of the chest. An example is presented of the results of this technique in a patient with agenesis of the hepatic segment of the inferior vena cava and azygos continuation.

Non-Hodgkin lymphoma in the porta hepatis after orthotopic liver transplantation: sonographic findings.

The sonographic appearances of primary non-Hodgkin lymphoma developing in the porta hepatis in three patients soon after hepatic transplantation were reviewed. The lymphomas appeared as large hypoechoic masses encasing vital portal structures--the hepatic artery and the common bile duct--in all three cases and displacing the portal vein in two. The liver was only locally involved. All patients presented with jaundice soon after transplantation (average interval, 6.3 months). Rapid tumor progression caused hepatic infarction, necessitating retransplantation in two patients. The third patient died shortly after diagnosis. The authors believe this complication will be seen increasingly as liver transplantation becomes more common. Non-Hodgkin lymphoma should be considered when an obstructing mass is found in the porta hepatis, even when the time interval since transplantation is short.

Postirradiation aortic sarcoma demonstrated by magnetic resonance angiography.

This is the first ever reported case of a radiation-induced aortic sarcoma. This patient had symptoms and signs initially interpreted as a pulmonary embolus. The extent of the disease was demonstrated with magnetic resonance imaging and magnetic resonance angiography, in particular, allowing rapid surgical intervention.

Comparison of transcranial color-coded sonography and magnetic resonance angiography in acute stroke.

BACKGROUND AND PURPOSE: We sought to compare the ability of transcranial color-coded Doppler sonography (TCCS) and magnetic resonance angiography (MRA) to identify circulatory changes that occur after acute stroke. METHODS: Forty-four patients with a clinical diagnosis of acute stroke were studied with both TCCS and MRA within 24 hours of stroke onset. The appearances of all vessels identified on MRA were divided into three categories: normal, attenuated, and absent vessels. The basal cerebral arteries were identified with the use of TCCS, and their velocities were measured with pulsed-wave Doppler. The side-to-side asymmetry was calculated and expressed as an asymmetry index. RESULTS: Five patients could not be studied with TCCS because of lack of a suitable acoustic window. An additional 4 patients were too restless to tolerate MRA scanning. Three patients had intracerebral hemorrhages, 2 patients had intracerebral gliomas, and the remaining 30 patients had cerebral infarctions. In the group of patients with acute cerebral infarction, TCCS identified 10 patients with normal asymmetry indices, 1 patient with an increased asymmetry index, 9 patients with decreased asymmetry indices, and 10 patients with occlusion of the symptomatic middle cerebral artery (MCA). MRA identified 8 normal angiograms, 6 patients had attenuated MCA branch vessels, 4 patients had MCA branch occlusions, 2 angiograms demonstrated MCA main stem attenuation, and 10 angiograms showed MCA occlusion. CONCLUSIONS: TCCS and MRA are both noninvasive techniques that can be used to study the acute stroke patient. They both yield information regarding the pathophysiology of acute stroke and may be useful techniques in deciding on therapeutic interventions. The findings agree closely with each other, and these techniques may be useful in the long-term follow-up of stroke patients.