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Conventional magnetic resonance imaging (MRI) is hampered by long scan times and only qualitative image contrasts that prohibit a direct comparison between different systems. To address these limitations, model-based reconstructions explicitly model the physical laws that govern the MRI signal generation. By formulating image reconstruction as an inverse problem, quantitative maps of the underlying physical parameters can then be extracted directly from efficiently acquired k-space signals without intermediate image reconstruction—addressing both shortcomings of conventional MRI at the same time. This review will discuss basic concepts of model-based reconstructions and report on our experience in developing several model-based methods over the last decade using selected examples that are provided complete with data and code. This article is part of the theme issue ‘Synergistic tomographic image reconstruction: part 1’.

Purpose Considerable inter-observer variability in the visual assessment of aneurysm recurrences limits its use as an outcome parameter evaluating new coil generations. The purpose of this study was to compare visual assessment of aneurysm recurrences and aneurysm recurrence volumetry with an example dataset of HydroSoft coils (HSC) versus bare platinum coils (BPC). Methods For this retrospective study, 3-dimensional time-of-flight magnetic resonance angiography datasets acquired 6 and 12 months after endovascular therapy using BPC only or mainly HSC were analyzed. Aneurysm recurrence volumes were visually rated by two observersas well as quantified by subtraction of the datasets after intensity-based rigid registration . Results A total of 297 aneurysms were analyzed (BPC: 169, HSC: 128). Recurrences were detected by aneurysm recurrence volumetry in 9 of 128 (7.0 %) treated with HSC and in 24 of 169 (14.2 %) treated with BPC (odds ratio: 2.39, 95 % confidence interval: 1.05–5.48; P  = 0.039). Aneurysm recurrence volumetry revealed an excellent correlation between observers (Cronbach’s alpha = 0.93). In contrast, no significant difference in aneurysm recurrence was found for visual assessment (3.9 % in HSC cases and 4.7 % in BPC cases). Recurrences were observed in aneurysms smaller than the sample median in 10 of 33 (30.3 %) by aneurysm recurrence volumetry and in 1 of 13 (7.7 %) by visual assessment. Conclusions Aneurysm recurrences were detected more frequently by aneurysm recurrence volumetry when compared with visual assessment. By using aneurysm recurrence volumetry, differences between treatment groups were detected with higher sensitivity and inter-observer validity probably because of the higher detection rate of recurrences in small aneurysms.

BackgroundDespite the increasing use of non-invasive imaging, DSA remains the gold standard for cerebrovascular imaging. However, trends in DSA utilization are poorly understood. The goal of this study was to describe DSA utilization in a large claims database in the US over a 13 year period.MethodsThis retrospective cohort study assessed a nationwide database of privately insured individuals from 2005 to 2018 for patients undergoing cranial CT angiography (CTA), MR angiography (MRA), and DSA. We assessed trends in the overall use of and indications for each modality. For DSA, we examined the types of performing proceduralists.ResultsAmong patients undergoing DSA in 2018, median age was 52 years, and 60% were women. MRA and DSA use decreased, from 289 to 275 claims, and from 38 to 29 claims per 100 000 enrollees, respectively, while CTA use increased from 31 to 286 claims per 100 000 enrollees. These trends differed by geographic region and indication. Nearly half of DSA procedures but <25% of non-invasive imaging were inpatient studies. DSA performed by neurosurgeons increased from 0.5 to 4.1 while those performed by radiologists decreased from 7.2 to 4.0 studies per 100 000 enrollees.ConclusionsDSA use decreased slightly while CTA use increased by ninefold. The reasons for this change are likely complex and may reflect more aggressive imaging for stroke, increased detection of incidental findings, and increased quality of non-invasive imaging. Over time, the proportion of DSA procedures performed by neurosurgeons overtook that performed by radiologists.

Objectives To determine and compare the diagnostic performance of stress myocardial perfusion imaging (MPI) for the diagnosis of obstructive coronary artery disease (CAD), using conventional coronary angiography (CCA) as the reference standard. Methods We searched Medline and Embase for literature that evaluated stress MPI for the diagnosis of obstructive CAD using magnetic resonance imaging (MRI), contrast-enhanced echocardiography (ECHO), single-photon emission computed tomography (SPECT) and positron emission tomography (PET). Results All pooled analyses were based on random effects models. Articles on MRI yielded a total of 2,970 patients from 28 studies, articles on ECHO yielded a sample size of 795 from 10 studies, articles on SPECT yielded 1,323 from 13 studies. For CAD defined as either at least 50 %, at least 70 % or at least 75 % lumen diameter reduction on CCA, the natural logarithms of the diagnostic odds ratio (lnDOR) for MRI (3.63; 95 % CI 3.26–4.00) was significantly higher compared to that of SPECT (2.76; 95 % CI 2.28–3.25; P  = 0.006) and that of ECHO (2.83; 95 % CI 2.29–3.37; P  = 0.02). There was no significant difference between the lnDOR of SPECT and ECHO ( P  = 0.52). Conclusion Our results suggest that MRI is superior for the diagnosis of obstructive CAD compared with ECHO and SPECT. ECHO and SPECT demonstrated similar diagnostic performance. Key Points • MRI can assess myocardial perfusion . • MR perfusion diagnoses coronary artery disease better than echocardiography or SPECT . • Echocardiography and SPECT have similar diagnostic performance . • MRI can save coronary artery disease patients from more invasive tests . • MRI and SPECT show evidence of publication bias, implying possible overestimation .

To assess the inter-technique agreement of relative cerebral blood volume (rCBV) measurements obtained using T1- and T2*-perfusion MRI on 3T scanner in glioma patients. A total of 49 adult patients with gliomas underwent both on T1- and T2*-perfusion in the same scanning session, and rCBV maps were estimated using both methods. For the quantitative analysis; Two independent observers recorded the rCBV values from the tumor as well as contralateral brain tissue from both T1- and T2*-perfusion. Inter-observer and inter-technique rCBV measurement agreement were determined by using 95% Bland-Altman limits of agreement and intra-class correlation coefficient (ICC) statistics. Qualitative analysis of the conventional and perfusion images showed that 16/49 (32.65%) tumors showed high susceptibility, and in these patients T2*-perfusion maps were suboptimal. Bland-Altman plots revealed an agreement between two independent observers recorded rCBV values for both T1- and T2*-perfusion. The ICC demonstrated strong agreement between rCBV values recorded by two observers for both T2* (ICC = 0.96, p = 0.040) and T1 (ICC = 0.97, p = 0.026) perfusion and similarly, good agreement was noted between rCBV estimated using two methods (ICC = 0.74, P<0.001). ROC analysis showed that rCBV estimated using T1- and T2*-perfusion methods were able to discriminate between grade-III and grade-IV tumors with AUC of 0.723 and 0.767 respectively. Comparison of AUC values of two ROC curves did not show any significant difference. In the current study, T1- and T2*-perfusion showed similar diagnostic performance for discrimination of grade III and grade IV gliomas; however, T1-perfusion was found to be better for the evaluation of tumors with intratumoral hemorrhage, postoperative recurrent tumors, and lesions near skull base. We conclude that T1-perfusion MRI with a single dose of contrast could be used as an alternative to T2*-perfusion to overcome the issues associated with this technique in brain tumors for reliable perfusion quantification.

Objectives To evaluate visualization of the right adrenal vein (RAV) with multidetector CT and non-contrast-enhanced MR imaging in patients with primary aldosteronism. Methods A total of 125 patients (67 men) scheduled for adrenal venous sampling (AVS) were included. Dynamic 64-detector-row CT and balanced steady-state free precession-based non-contrast-enhanced 3-T MR imaging were performed. RAV visualization based on a four-point score was documented. Both anatomical location and variation on cross-sectional imaging were evaluated, and the findings were compared with catheter venography as the gold standard. Results The RAV was visualized in 93.2 % by CT and 84.8 % by MR imaging ( p  = 0.02). Positive predictive values of RAV visualization were 100 % for CT and 95.2 % for MR imaging. Imaging score was significantly higher in CT than MR imaging ( p  < 0.01). The RAV formed a common trunk with an accessory hepatic vein in 16 % of patients. The RAV orifice level on cross-sectional imaging was concordant with catheter venography within the range of 1/3 vertebral height in >70 % of subjects. Success rate of AVS was 99.2 %. Conclusions Dynamic CT is a reliable way to map the RAV prior to AVS. Non-contrast-enhanced MR imaging is an alternative when there is a risk of complication from contrast media or radiation exposure. Key Points • Dynamic CT and non-contrast-enhanced MR imaging detect the right adrenal vein (RAV). • Dynamic CT can visualize the RAV more than non-contrast-enhanced MR imaging. • Mapping the RAV helps to achieve successful adrenal venous sampling. • Sixteen per cent of RAVs share the common trunk with accessory hepatic veins.

The aim of the study was to evaluate the role of pseudocontinuous arterial spin labeling perfusion (pCASL-perfusion) in preoperative assessment of cerebral glioma grades. The study group consisted of 253 patients, aged 7–78 years with supratentorial gliomas (65 low-grade gliomas (LGG), 188 high-grade gliomas (HGG)). We used 3D pCASL-perfusion for each patient in order to calculate the tumor blood flow (TBF). We obtained maximal tumor blood flow (maxTBF) in small regions of interest (30 ± 10 mm 2 ) and then normalized absolute maximum tumor blood flow (nTBF) to that of the contralateral normal-appearing white matter of the centrum semiovale. MaxTBF and nTBF values significantly differed between HGG and LGG groups ( p  < 0.001), as well as between patient groups separated by the grades (grade II vs. grade III) ( p  < 0.001). Moreover, we performed ROC-analysis which demonstrated high sensitivity and specificity in differentiating between HGG and LGG. We found significant differences for maxTBF and nTBF between grade III and IV gliomas, however, ROC-analysis showed low sensitivity and specificity. We did not observe a significant difference in TBF for astrocytomas and oligodendrogliomas. Our study demonstrates that 3D pCASL-perfusion as an effective diagnostic tool for preoperative differentiation of glioma grades.

Background Stroke and other non-communicable diseases are important emerging public health concerns in sub-Saharan Africa where stroke-related mortality and morbidity are higher compared to other parts of the world. Despite the availability of evidence-based acute stroke interventions globally, uptake in low-middle income countries (LMIC) such as Ghana is uncertain. This study aimed to identify and evaluate available acute stroke services in Ghana and the extent to which these services align with global best practice. Methods A multi-site, hospital-based survey was conducted in 11 major referral hospitals (regional and tertiary - teaching hospitals) in Ghana from November 2015 to April 2016. Respondents included neurologists, physician specialists and medical officers (general physicians). A pre-tested, structured questionnaire was used to gather data on available hospital-based acute stroke services in the study sites, using The World Stroke Organisation Global Stroke Services Guideline as a reference for global standards. Results Availability of evidence-based services for acute stroke care in the study hospitals were varied and limited. The results showed one tertiary-teaching hospital had a stroke unit. However, thrombolytic therapy (thrombolysis) using recombinant tissue plasminogen activator for acute ischemic stroke care was not available in any of the study hospitals. Aspirin therapy was administered in all the 11 study hospitals. Although eight study sites reported having a brain computed tomographic (CT) scan, only 7 (63.6%) were functional at the time of the study. Magnetic resonance imaging (MRI scan) services were also limited to only 4 (36.4%) hospitals (only functional in three). Acute stroke care by specialists, especially neurologists, was found in 36.4% (4) of the study hospitals whilst none of the study hospitals had an occupational or a speech pathologist to support in the provision of acute stroke care. Conclusion This study confirms previous reports of limited and variable provision of evidence based stroke services and the low priority for stroke care in resource poor settings. Health policy initiatives to enhance uptake of evidence-based acute stroke services is required to reduce stroke-related mortality and morbidity in countries such as Ghana.

Background Cerebral angiography remains the gold standard for the detection of mycotic aneurysms, and it has been estimated that ruptured mycotic aneurysms result in 5% of the neurological complications of patients with infective endocarditis (IE). Objective To determine the diagnostic yield of cerebral angiography in the above patient population and to assess patient factors that might suggest greater or lesser utility. Methods We retrospectively reviewed 168 patients who underwent cerebral angiography with a diagnosis of IE or infected left ventricular assist device at the Cleveland Clinic between January 2003 and March 2010 in accordance with institutional review board guidelines. Chart and imaging review was performed. Results 15/168 patients (8.9%) had mycotic aneurysms; 93.3% (14/15) of the patients with mycotic aneurysms presented with CNS hemorrhage and 66.7% (10/15) had acute ischemic findings. Of the 15 patients with mycotic aneurysms on angiography, seven underwent CT angiography and six underwent MR angiography, which showed mycotic aneurysms in three (42.9%) and two cases (one of which was questionable; 33.3%), respectively. Conclusions Patients with IE or similar sources of central bacterial emboli are prone to neurovascular complications. Approximately 9% of patients with IE at our institution who undergo cerebral angiography have mycotic aneurysms. Presentation with hemorrhage appears to be more predictive of aneurysm, as approximately 22% of patients with IE and hemorrhage were found to have an aneurysm compared with only 1% when hemorrhage was absent. Thus, patients with IE presenting with intracranial hemorrhage should undergo vascular imaging, preferably with cerebral angiography.

Objectives The purpose of this study was to determine the accuracy and utility of contrast-enhanced MR angiography (CE-MRA) in spinal dural arteriovenous fistulas (SDAVF). Methods A retrospective analysis from 1999–2012 identified 70 patients clinically suspected of harboring a SDAVF. Each patient underwent consecutive conventional MR-imaging, CE-MRA, and digital subtraction angiography (DSA). The presence or absence of serpentine flow voids, T2-weighted hyperintensity, and cord enhancement were evaluated, as well as location of the fistula as predicted by CE-MRA. DSA was used as the reference standard. Results Of the 70 cases, 53 were determined to be a SDAVF, 10 cases were shown to be other forms of vascular malformation, and 7 were DSA-negative. On MRI, all reported cases of SDAVF showed serpentine flow voids (100 %). T2-weighted hyperintensity was seen in 48 of 50 cases (96 %), extending to the conus in 41 of 48 cases (85 %). Cord enhancement was seen in 38 of 41 cases (93 %). CE-MRA correctly localized the SDAVF in 43 of the 53 cases (81 %). Conclusions CE-MRA is a useful non-invasive examination for the detection and localization of SDAVF. CE-MRA facilitates but does not replace DSA as confirmation of location, fistula type, and arterial detail, which are required before treatment. Key Points • CE-MRA correctly localized the site of the SDAVF in over 80 % of cases. • CE-MRA facilitates diagnostic DSA and expedites the diagnostic process. • CE-MRA does not replace diagnostic DSA in SDAVF cases as confirmative test. • CE-MRA provides better understanding of missed or mislocalized SDAVF cases.