Advanced risk prediction for aortic dissection patients using imaging-based computational flow analysis.

Patients with either a repaired or medically managed aortic dissection have varying degrees of risk of developing late complications. High-risk patients would benefit from earlier intervention to improve their long-term survival. Currently serial imaging is used for risk stratification, which is not always reliable. On the other hand, understanding aortic haemodynamics within a dissection is essential to fully evaluate the disease and predict how it may progress. In recent decades, computational fluid dynamics (CFD) has been extensively applied to simulate complex haemodynamics within aortic diseases, and more recently, four-dimensional (4D)-flow magnetic resonance imaging (MRI) techniques have been developed for in vivo haemodynamic measurement. This paper presents a comprehensive review on the application of image-based CFD simulations and 4D-flow MRI analysis for risk prediction in aortic dissection. The key steps involved in patient-specific CFD analyses are demonstrated. Finally, we propose a workflow incorporating computational modelling for personalised assessment to aid in risk stratification and treatment decision-making.

Imaging of transcatheter aortic valve replacement complications.

Aortic stenosis is increasing in incidence and is now commonly managed with transcatheter aortic valve replacement (TAVR) in intermediate and high-risk patients. Radiologists are likely to encounter patients undergoing this procedure both pre- and postoperatively, and therefore, an understanding of procedural complications is essential. Complications may relate to the access site or approach, or the valve itself. This article will review the most common complications described in literature and focuses on the role of multidetector computed tomography (CT) in their evaluation either exclusively, or complementary to other imaging methods.

Bioprosthetic valve thrombosis and degeneration following transcatheter aortic valve implantation (TAVI).

Bioprosthetic valve thrombosis (BPVT) is a recognised complication of prosthetic aortic valves and can be found in up to 13% of patients after transcatheter implantation. The mechanism of BPVT is not well known, abnormal flow conditions in the new and native sinuses and lack of functional endothelialisation are suspected causes. BPVT may result in valve dysfunction, possibly related to degeneration, and recurrence of patient symptoms, or remain subclinical. BPVT is best diagnosed at multiphase gated computed tomography (CT) angiography as the presence of reduced leaflet motion (RELM) and hypoattenuating aortic leaflet thickening (HALT). Although CT is used to exclude BPVT in symptomatic patients and those with increased valve gradients, the value of screening and prophylactic anticoagulation is debatable.

Display colour scale effects on diagnostic performance and reader agreement in cardiac CT and prostate apparent diffusion coefficient assessment.

AIM: To investigate the effect of colour scale choice on diagnostic performance in the interpretation of medical images. MATERIALS AND METHODS: Twelve clinicians interpreted 210 myocardial computed tomography (CT) perfusion (CTP) examinations, and nine clinicians interpreted 165 magnetic resonance imaging (MRI) apparent diffusion coefficient (ADC) prostate images. In three separate sessions, each participant read the same image set using greyscale, hot-iron, and rainbow scales, respectively. Participants scored their level of confidence for tumour presence in the ADC study, and for ischaemia in the CTP study, from 0 to 100. The area under the receiver operating characteristic (ROC) curve (AUC) was used as the performance metric. For cases that scored >50, CTP readers' agreement on the ischaemic transmural extent was analysed, and ADC map readers' selected values and coordinates for the lowest ADC within the detected tumour were compared across different colour scales. RESULTS: For CTP detection, the AUC was up to 0.10 higher with greyscale, 0.67±0.02 (standard error), compared to rainbow, 0.56±0.02, and detection with hot-iron was in between (0.61±0.03). For ischaemic transmural lesion categorisation, observed inter-reader agreement was highest with greyscale for category 25-50%. There is a small tendency for rainbow and greyscale to outperform hot-iron in the detection of prostate tumours. The selected lowest ADC value and pixel localisation was similar with all colour scales. CONCLUSIONS: The present findings suggest that colour visualisation has a measurable effect on CTP and ADC performance. Further investigation is necessary to determine the magnitude of the effect in diagnostic tasks.

Trans Arterial Embolization of Spontaneous Intra-Abdominal Haemorrhage from Omental Lipoma.

We describe 3 cases of omental lipoma of whom 2 presented with symptomatic haemorrhage. Notably the haemorrhage in the 2 reported cases was from foregut arteries. Thorough knowledge of anatomy and embryology is critical in identifying the source of haemorrhage and differentiating this condition from other common causes of mesenteric haemorrhage. To the best of our knowledge, this is the first case series reporting this uncommon cause for abdominal haemorrhage. The successful management of this condition using superselective embolization is discussed. Clinicians need to exercise diligence and caution in omental lipomas presenting with spontaneous haemorrhage and this notion is exemplified in our reported cases.

Multimodality quantitative assessments of myocardial perfusion using dynamic contrast enhanced magnetic resonance and 15O-labelled water positron emission tomography imaging.

Kinetic modelling of myocardial perfusion imaging data allows the absolute quantification of myocardial blood flow (MBF) and can improve the diagnosis and clinical assessment of coronary artery disease (CAD). Positron emission tomography (PET) imaging is considered the reference standard technique for absolute quantification, whilst oxygen-15 (15O)-water has been extensively implemented for MBF quantification. Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) has also been used for MBF quantification and showed comparable diagnostic performance against (15O)-water PET studies. We investigated for the first time the diagnostic performance of two different PET MBF analysis softwares PMOD and Carimas, for obstructive CAD detection against invasive clinical standard methods in 20 patients with known or suspected CAD. Fermi and distributed parameter modelling-derived MBF quantification from DCE-MRI was also compared against (15O)-water PET, in a subgroup of 6 patients. The sensitivity and specificity for PMOD was significantly superior for obstructive CAD detection in both per vessel (0.83, 0.90) and per patient (0.86, 0.75) analysis, against Carimas (0.75, 0.65), (0.81, 0.70), respectively. We showed strong, significant correlations between MR and PET MBF quantifications (r=0.83-0.92). However, DP and PMOD analysis demonstrated comparable and higher haemodynamic differences between obstructive versus (no, minor or non)-obstructive CAD, against Fermi and Carimas analysis. Our MR method assessments against the optimum PET reference standard technique for perfusion analysis showed promising results in per segment level and can support further multi-modality assessments in larger patient cohorts. Further MR against PET assessments may help to determine their comparative diagnostic performance for obstructive CAD detection.

Assessment of myocardial fibrosis with T1 mapping MRI.

Myocardial fibrosis can arise from a range of pathological processes and its presence correlates with adverse clinical outcomes. Cardiac magnetic resonance (CMR) can provide a non-invasive assessment of cardiac structure, function, and tissue characteristics, which includes late gadolinium enhancement (LGE) techniques to identify focal irreversible replacement fibrosis with a high degree of accuracy and reproducibility. Importantly the presence of LGE is consistently associated with adverse outcomes in a range of common cardiac conditions; however, LGE techniques are qualitative and unable to detect diffuse myocardial fibrosis, which is an earlier form of fibrosis preceding replacement fibrosis that may be reversible. Novel T1 mapping techniques allow quantitative CMR assessment of diffuse myocardial fibrosis with the two most common measures being native T1 and extracellular volume (ECV) fraction. Native T1 differentiates normal from infarcted myocardium, is abnormal in hypertrophic cardiomyopathy, and may be particularly useful in the diagnosis of Anderson-Fabry disease and amyloidosis. ECV is a surrogate measure of the extracellular space and is equivalent to the myocardial volume of distribution of the gadolinium-based contrast medium. It is reproducible and correlates well with fibrosis on histology. ECV is abnormal in patients with cardiac failure and aortic stenosis, and is associated with functional impairment in these groups. T1 mapping techniques promise to allow earlier detection of disease, monitor disease progression, and inform prognosis; however, limitations remain. In particular, reference ranges are lacking for T1 mapping values as these are influenced by specific CMR techniques and magnetic field strength. In addition, there is significant overlap between T1 mapping values in healthy controls and most disease states, particularly using native T1, limiting the clinical application of these techniques at present.

Ten years of imaging for pulmonary embolism: too many scans or the tip of an iceberg?

AIM: To examine the number and nature of investigations performed for suspected pulmonary embolism (PE) in a large teaching hospital and the change in incidence and severity of PE over a decade. MATERIALS AND METHODS: In this retrospective study, all patients investigated for suspected PE using computed tomography pulmonary angiography (CTPA) or lung scintigraphy during 10 years to March 2012 were identified and their records reviewed. In the final year, all reportedly positive CTPA cases were reviewed and PE severity calculated, for comparison with similar historical data. RESULTS: From 2002 to 2012, total annual investigations for suspected acute PE increased by 163% (805 to 2121). CTPA increased by 325% (475 to 2019). Detection of PE increased by 121% (193 to 426 per annum), with stable distribution of severity scores. The positive scan rate decreased from 24% to 20%. The mean age of patients being investigated for PE increased from 56 to 63 years. CONCLUSIONS: Increased detection of PE is not due to disproportionate increase in small PEs, but to increased detection of PE of all severities. This finding supports the hypothesis that PE is more common in the general population than previously appreciated, which may represent an iceberg phenomenon of previously undetected disease.

Perioperative elafin for ischaemia-reperfusion injury during coronary artery bypass graft surgery: a randomised-controlled trial.

BACKGROUND: Elafin is a potent endogenous neutrophil elastase inhibitor that protects against myocardial inflammation and injury in preclinical models of ischaemic-reperfusion injury. We investigated whether elafin could inhibit myocardial ischaemia-reperfusion injury induced during coronary artery bypass graft (CABG) surgery. METHODS AND RESULTS: In a randomised double-blind placebo-controlled parallel group clinical trial, 87 patients undergoing CABG surgery were randomised 1:1 to intravenous elafin 200 mg or saline placebo administered after induction of anaesthesia and prior to sternotomy. Myocardial injury was measured as cardiac troponin I release over 48 h (area under the curve (AUC)) and myocardial infarction identified with MRI. Postischaemic inflammation was measured by plasma markers including AUC high-sensitive C reactive protein (hs-CRP) and myeloperoxidase (MPO). Elafin infusion was safe and resulted in >3000-fold increase in plasma elafin concentrations and >50% inhibition of elastase activity in the first 24 h. This did not reduce myocardial injury over 48 h (ratio of geometric means (elafin/placebo) of AUC troponin I 0.74 (95% CI 0.47 to 1.15, p=0.18)) although post hoc analysis of the high-sensitive assay revealed lower troponin I concentrations at 6 h in elafin-treated patients (median 2.4 vs 4.1 µg/L, p=0.035). Elafin had no effect on myocardial infarction (elafin, 7/34 vs placebo, 5/35 patients) or on markers of inflammation: mean differences for AUC hs-CRP of 499 mg/L/48 h (95% CI -207 to 1205, p=0.16), and AUC MPO of 238 ng/mL/48 h (95% CI -235 to 711, p=0.320). CONCLUSIONS: There was no strong evidence that neutrophil elastase inhibition with a single-dose elafin treatment reduced myocardial injury and inflammation following CABG-induced ischaemia-reperfusion injury. TRIAL REGISTRATION NUMBER: (EudraCT 2010-019527-58, ISRCTN82061264).

Feasibility of radiation dose reduction using AIDR-3D in dynamic pulmonary CT perfusion.

AIM: To assess the feasibility of radiation dose reduction with adaptive iterative dose reduction (AIDR-6 3D) reconstruction in dynamic pulmonary CT perfusion. MATERIALS AND METHODS: CTP examinations of 10 patients acquired at 100 kVp/50 mAs were reconstructed with filtered back projection (FBP) and AIDR-3D. Artificial noise was added to raw data (pre-reconstruction projection data) to simulate lower tube current scanning. Radiodensity (in Hounsfield units), noise, and perfusion values were compared. RESULTS: There was no significant difference in noise between the full and simulated reduced tube current with AIDR-3D reconstruction (p = 1). There was significantly lower noise in lung tissue with AIDR-3D images when compared to reconstructions without AIDR-3D (p = 0.005) and no significant change in the radiodensity (p = 1; mean difference <6 HU). Mean perfusion values increased significantly at lower tube currents (25 and 12.5 mAs), compared to 50 mAs (p = 0.005). This effect was significantly greater in larger patients compared to thin patients. CONCLUSION: AIDR-3D produced significantly lower noise images than FBP-based algorithms and maintained consistent noise levels in lung at 12.5 mAs, indicating this algorithm is suitable for reduced dose lung perfusion imaging. Iterative reconstruction allows significant radiation dose reduction of up to fourfold in smaller patients, and up to twofold in the medium/large size patients. The increase in perfusion values at 25% simulated tube currents is attributed to attenuation bias.

Imaging of cardiovascular risk in patients with Turner's syndrome.

Turner's syndrome is a disorder defined by an absent or structurally abnormal second X chromosome and affects around 1 in 2000 newborn females. The standardised mortality ratio in Turner's syndrome is around three-times higher than in the general female population, mainly as a result of cardiovascular disorders. Most striking is the early age at which Turner's syndrome patients develop the life-threatening complications of cardiovascular disorders compared to the general population. The cardiovascular risk stratification in Turner's syndrome is challenging and imaging is not systematically used. The aim of this article is to review cardiovascular risks in this group of patients and discuss a systematic imaging approach for early identification of cardiovascular disorders in these patients.

Iterative reconstruction and individualized automatic tube current selection reduce radiation dose while maintaining image quality in 320-multidetector computed tomography coronary angiography.

AIM: To assess the effect of two iterative reconstruction algorithms (AIDR and AIDR3D) and individualized automatic tube current selection on radiation dose and image quality in computed tomography coronary angiography (CTCA). MATERIALS AND METHODS: In a single-centre cohort study, 942 patients underwent electrocardiogram-gated CTCA using a 320-multidetector CT system. Images from group 1 (n = 228) were reconstructed with a filtered back projection algorithm (Quantum Denoising Software, QDS+). Iterative reconstruction was used for group 2 (AIDR, n = 379) and group 3 (AIDR3D, n = 335). Tube current was selected based on body mass index (BMI) for groups 1 and 2, and selected automatically based on scout image attenuation for group 3. Subjective image quality was graded on a four-point scale (1 = excellent, 4 = non-diagnostic). RESULTS: There were no differences in age (p = 0.975), body mass index (p = 0.435), or heart rate (p = 0.746) between the groups. Image quality improved with iterative reconstruction and automatic tube current selection [1.3 (95% confidence intervals (CI): 1.2-1.4), 1.2 (1.1-1.2) and 1.1 (1-1.2) respectively; p < 0.001] and radiation dose decreased [274 (260-290), 242 (230-253) and 168 (156-180) mGy cm, respectively; p < 0.001]. CONCLUSION: The application of the latest iterative reconstruction algorithm and individualized automatic tube current selection can substantially reduce radiation dose whilst improving image quality in CTCA.

Aortic stenosis, atherosclerosis, and skeletal bone: is there a common link with calcification and inflammation?

AIMS: The pathophysiology of aortic stenosis shares many similarities with atherosclerosis and skeletal bone formation. Using non-invasive imaging, we compared aortic valve calcification and inflammation activity with that measured in atherosclerosis and bone. METHODS AND RESULTS: Positron emission and computed tomography was performed using 18F-sodium fluoride (18F-NaF, calcification) and 18F-fluorodeoxyglucose (18F-FDG, inflammation) in 101 patients with calcific aortic valve disease (81 aortic stenosis and 20 aortic sclerosis). Calcium scores and positron emission tomography tracer activity (tissue-to-background ratio; TBR) were measured in the aortic valve, coronary arteries, thoracic aorta, and bone. Over 90% of the cohort had coexistent calcific atheroma, yet correlations between calcium scores were weak or absent (valve vs. aorta r(2) = 0.015, P = 0.222; valve vs. coronaries r(2) = 0.039, P = 0.049) as were associations between calcium scores and bone mineral density (BMD vs. valve r(2) = 0.000, P = 0.766; vs. aorta r(2) = 0.052, P = 0.025; vs. coronaries r(2) = 0.016, P = 0.210). 18F-NaF activity in the valve was 28% higher than in the aorta (TBR: 2.66 ± 0.84 vs. 2.11 ± 0.31, respectively, P < 0.001) and correlated more strongly with the severity of aortic stenosis (r(2) = 0.419, P < 0.001) than 18F-NaF activity outwith the valve (valve vs. aorta r(2) = 0.167, P < 0.001; valve vs. coronary arteries r(2) = 0.174, P < 0.001; valve vs. bone r(2) = 0.001, P = 0.806). In contrast, 18F-FDG activity was lower in the aortic valve than the aortic atheroma (TBR: 1.56 ± 0.21 vs. 1.81 ± 0.24, respectively, P < 0.001) and more closely associated with uptake outwith the valve (valve vs. aorta r(2) = 0.327, P < 0.001). CONCLUSION: In patients with aortic stenosis, disease activity appears to be determined by local calcific processes within the valve that are distinct from atherosclerosis and skeletal bone metabolism.

MRI of the lung (3/3)-current applications and future perspectives.

BACKGROUND: MRI of the lung is recommended in a number of clinical indications. Having a non-radiation alternative is particularly attractive in children and young subjects, or pregnant women. METHODS: Provided there is sufficient expertise, magnetic resonance imaging (MRI) may be considered as the preferential modality in specific clinical conditions such as cystic fibrosis and acute pulmonary embolism, since additional functional information on respiratory mechanics and regional lung perfusion is provided. In other cases, such as tumours and pneumonia in children, lung MRI may be considered an alternative or adjunct to other modalities with at least similar diagnostic value. RESULTS: In interstitial lung disease, the clinical utility of MRI remains to be proven, but it could provide additional information that will be beneficial in research, or at some stage in clinical practice. Customised protocols for chest imaging combine fast breath-hold acquisitions from a "buffet" of sequences. Having introduced details of imaging protocols in previous articles, the aim of this manuscript is to discuss the advantages and limitations of lung MRI in current clinical practice. CONCLUSION: New developments and future perspectives such as motion-compensated imaging with self-navigated sequences or fast Fourier decomposition MRI for non-contrast enhanced ventilation- and perfusion-weighted imaging of the lung are discussed. Main Messages • MRI evolves as a third lung imaging modality, combining morphological and functional information. • It may be considered first choice in cystic fibrosis and pulmonary embolism of young and pregnant patients. • In other cases (tumours, pneumonia in children), it is an alternative or adjunct to X-ray and CT. • In interstitial lung disease, it serves for research, but the clinical value remains to be proven. • New users are advised to make themselves familiar with the particular advantages and limitations.

Radiology curriculum for undergraduate medical studies--a consensus survey.

AIM: To establish an expert consensus of what, when, and how the teaching of radiology should be incorporated into the core undergraduate medical curriculum. METHODS AND MATERIALS: This Delphi survey consisted of four iterative rounds, with feedback given at the start of each successive round in the form of the results of the previous round. The participants consisted of both radiologists and non-radiologists with significant interest and involvement in radiology and undergraduate/Foundation training. The study addressed the questions of how, where, when, and by whom radiology should be taught. RESULTS: The number of responses in rounds 1-4 was 20, 23, 41, and 25 (25, 22, 31, and 61% response rate, respectively). There was good consensus amongst the responders on the following: radiology teaching must be delivered in conjunction with anatomy and clinical case-based teaching, if possible in the department of radiology on picture archiving and communication system (PACS) workstations, and the teaching should be delivered by a competent and credentialled individual. Case-based assessment was the most agreed method of assessment. The majority of the responders concurred that the curriculum should include general indications for commonly requested radiological investigations, consent and safety issues around radiological tests, and their basic interpretation. CONCLUSION: The consensus points reached by the present study not only serve as directive principles for developing a more comprehensive radiology curriculum, but also places emphasis on a broader range of knowledge required to promote the best use of a department of radiology by junior doctors in an attempt to improve patient experiences and care.

Embolization for non-variceal upper gastrointestinal tract haemorrhage: a systematic review.

AIM: To assess the published evidence on the endovascular treatment of non-variceal upper gastrointestinal haemorrhage. MATERIALS AND METHODS: An Ovid Medline search of published literature was performed (1966-2009). Non-English literature, experimental studies, variceal haemorrhage and case series with fewer than five patients were excluded. The search yielded 1888 abstracts. Thirty-five articles were selected for final analysis. RESULTS: The total number of pooled patients was 927. The technical and clinical success of embolization ranged from 52-100% and 44-100%, respectively. The pooled mean technical/clinical success rate in primary upper gastrointestinal tract haemorrhage (PUGITH) only, trans-papillary haemorrhage (TPH) only, and mixed studies were 84%/67%, 93%/89%, and 93%/64%, respectively. Clinical outcome was adversely affected by multi-organ failure, shock, corticosteroids, transfusion, and coagulopathy. The anatomical source of haemorrhage and procedural variables did not affect the outcome. A successful embolization improved survival by 13.3 times. Retrospective comparison with surgery demonstrated equivalent mortality and clinical success, despite embolization being applied to a more elderly population with a higher prevalence of co-morbidities. CONCLUSIONS: Embolization is effective in this very difficult cohort of patients with outcomes similar to surgery.