1,428 research outputs found
A Semi-parametric Technique for the Quantitative Analysis of Dynamic Contrast-enhanced MR Images Based on Bayesian P-splines
Dynamic Contrast-enhanced Magnetic Resonance Imaging (DCE-MRI) is an
important tool for detecting subtle kinetic changes in cancerous tissue.
Quantitative analysis of DCE-MRI typically involves the convolution of an
arterial input function (AIF) with a nonlinear pharmacokinetic model of the
contrast agent concentration. Parameters of the kinetic model are biologically
meaningful, but the optimization of the non-linear model has significant
computational issues. In practice, convergence of the optimization algorithm is
not guaranteed and the accuracy of the model fitting may be compromised. To
overcome this problems, this paper proposes a semi-parametric penalized spline
smoothing approach, with which the AIF is convolved with a set of B-splines to
produce a design matrix using locally adaptive smoothing parameters based on
Bayesian penalized spline models (P-splines). It has been shown that kinetic
parameter estimation can be obtained from the resulting deconvolved response
function, which also includes the onset of contrast enhancement. Detailed
validation of the method, both with simulated and in vivo data, is provided
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Turbulent jet from a slender annular slot ventilated by a self-induced flow through the open core
The dynamics of an incompressible turbulent air jet from an annular source into otherwise quiescent surroundings are investigated. Focussing on a slender annulus with an open core, the development of the jet is examined using planar and stereoscopic particle image
velocimetry (PIV) from the source to 16 (outer) source diameters downstream. Unique to these annular sources, the jet induces a
flow through the open core - in other words, the core is `ventilated'. Our measurements indicate that the volume flux drawn through the
core exceeds that from the source by approximately 20%. Based on the streamwise development of the jet, we identify four distinct regions: (i) an internal region of induced flow that is bounded by the jet; (ii) a near-field planar-jet-like region; (iii) a transition region; and, ultimately, (iv) a far- field round-jet-like region. We explore the evolution of the jet
towards self-similar behaviour based on cross-stream profiles of time-averaged velocity and turbulence statistics within these different regions. Four distinct length scales are shown to characterise the streamwise extents and behaviours within the regions identified. Finally, to
highlight the role of the open-core (ventilated) annular geometry on jet development, comparisons are made with PIV measurements of turbulent jets issuing from circular sources. These comparisons reveal that the ventilated geometry significantly enhances dilution in the
near field.The authors G.R.H. and S.P. gratefully acknowledge the financial support of Dyson Technology Ltd and the EPSRC Industrial Case Award programme 13440009
Bone imaging in prostate cancer: the evolving roles of nuclear medicine and radiology
The bone scan continues to be recommended for both the staging and therapy response assessment of skeletal metastases from prostate cancer. However, it is widely recognised that bone scans have limited sensitivity for disease detection and is both insensitive and non-specific for determining treatment response, at an early enough time point to be clinically useful. We, therefore, review the evolving roles of nuclear medicine and radiology for this application. We have reviewed the published literature reporting recent developments in imaging bone metastases in prostate cancer, and provide a balanced synopsis of the state of the art. The development of single-photon emission computed tomography combined with computed tomography has improved detection sensitivity and specificity but has not yet been shown to lead to improvements in monitoring therapy. A number of bone-specific and tumour-specific tracers for positron emission tomography/computed tomography (PET/CT) are now available for advanced prostate cancer that show promise in both clinical settings. At the same time, the development of whole-body magnetic resonance imaging (WB-MRI) that incorporates diffusion-weighted imaging also offers significant improvements for detection and therapy response assessment. There are emerging data showing comparative SPECT/CT, PET/CT, and WB-MRI test performance for disease detection, but no compelling data on the usefulness of these technologies in response assessment have yet emerged
Fast Magnetic Resonance Imaging as a Viable Method for Directing the Prostate Cancer Diagnostic Pathway
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The development of turbulent slender open-core annular jets
The very first study of the development of the turbulent isothermal and incompressible air jet which issues at a constant velocity from a slender annular slot, circumnavigating an open core, into an otherwise quiescent and unbounded environment of the same density, is presented. The geometry of this source is defined by three diameters: the outer diameter of the slot ; the inner diameter of the slot ; and the diameter of the (circular) open core . `Slender' refers to a slot for which the inner and outer diameters are approximately equal, i.e. . Our focus lies in understanding the development of the time-averaged flow with distance downstream and the influence of the source geometry on the development of the jet.
Given the absence of information on jets issuing from the sources of interest, the investigation follows an approach reminiscent of the classic investigations into round jets. That is, it begins with the development of a nozzle and experimental set-up which are suitable for studying the slender open-core annular jet. In addition to the experimental measurements, a complementary mathematical model was developed to describe the unique near-field behaviour of the open-core jet. Measurements were acquired using flow visualisation and Particle Image Velocimetry. On examining the streamwise development of the flow, the slender almost fully open-core jet was delineated into four key regions and the characteristic scalings identified. The regions were as follows: a bounded induced-flow region; a near-source planar-jet region; a transitional region; and a far-field round-jet region. Fluid induced through the open core of the nozzle and subsequently entrained into the jet significantly enhanced the near-field dilution of the jet.
Following on from this, the influence of the diameter ratio and ventilation ratio on jet coalescence was examined. Over the range of diameter ratios examined (), experimental measurements and the predictions from mathematical modelling indicated that significantly influenced the volume flux induced through the core while the coalescing behaviour of the jet and the far-field region remained largely unchanged.
Over the range of ventilation ratios examined (), experimental measurements demonstrated that controlled the restriction experienced by fluid induced through the open core and significantly influenced the far-field behaviour of the jet.
Our findings suggest that jet of interest is then uniquely characterised by the momentum flux , the diameter ratio , and the ventilation ratio .EPSRC Industrial CASE award - Dyson Ltd
Developments in MRI-targeted prostate biopsy
PURPOSE OF REVIEW: MRI-targeted prostate biopsy may be an attractive alternative to systematic biopsy for diagnosing clinically significant prostate cancer. In this narrative review, we discuss the new developments that have occurred in the advancement of MRI-targeted prostate biopsy, over the past 24 months. RECENT FINDINGS: MRI-targeted biopsy offers enhanced diagnostic accuracy, when compared with the current standard of care of systematic transrectal ultrasound-guided (TRUS) biopsy, by decreasing the overall number of biopsies needed, maintaining or improving significant prostate cancer detection, and reducing the detection of clinically insignificant prostate cancer. The necessity of combining systematic prostate biopsy with MRI-targeted biopsy is still debated. The use of MRI--ultrasound fusion systems for lesion-targeting is promising for optimizing significant cancer detection, but recent evidence suggests that additional cognitive biopsy cores are still useful in detecting additional cancers. SUMMARY: MRI-targeted biopsy in selected men with positive MRI offers a number of benefits over systematic biopsy in all men, and as such, may emerge as the new standard of care for the diagnosis of clinically significant prostate cancer
Whole-body magnetic resonance imaging (WB-MRI) for cancer screening in asymptomatic subjects of the general population: review and recommendations.
BACKGROUND:The number of studies describing the use of whole-body magnetic resonance imaging (WB-MRI) for screening of malignant tumours in asymptomatic subjects is increasing. Our aim is to review the methodologies used and the results of the published studies on per patient and per lesion analysis, and to provide recommendations on the use of WB-MRI for cancer screening. MAIN BODY:We identified 12 studies, encompassing 6214 WB-MRI examinations, which provided the rates of abnormal findings and findings suspicious for cancer in asymptomatic subjects, from the general population. Eleven of 12 studies provided imaging protocols that included T1- and T2-weighted sequences, while only five included diffusion weighted imaging (DWI) of the whole body. Different categorical systems were used for the classification and the management of abnormal findings. Of 17,961 abnormal findings reported, 91% were benign, while 9% were oncologically relevant, requiring further investigations, and 0.5% of lesions were suspicious for cancer. A per-subject analysis showed that just 5% of subjects had no abnormal findings, while 95% had abnormal findings. Findings requiring further investigation were reported in 30% of all subjects, though in only 1.8% cancer was suspected. The overall rate of histologically confirmed cancer was 1.1%. CONCLUSION:WB-MRI studies of cancer screening in the asymptomatic general population are too heterogeneous to draw impactful conclusions regarding efficacy. A 5-point lesion scale based on the oncological relevance of findings appears the most appropriate for risk-based management stratification. WB-MRI examinations should be reported by experienced oncological radiologists versed on WB-MRI reading abnormalities and on onward referral pathways
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