Impact of Local Arterial Compliance and Shear Stress on Baroreceptor Function in Children with Repaired Coarctation of the Aorta

Phase contrast MRI images of the ascending and descending aorta; magnitude (top) and velocity (bottom)

Kenny D, Curtis S, Polson J, Martin RP, Wilson DG, Caputo M, Hartley Davies R, Cockcroft JR, Paton JFR, Wolf AR, Hamilton M.

Bristol Heart Institute, Medical Physics & Bioengineering, University Hospitals Bristol and Weston NHS Foundation Trust, University of Bristol, Bristol Congenital Heart Centre, and University of Wales

Aim

MRI may be used to evaluate local arterial compliance and shear stress that may influence arterial remodelling in patients with repaired  coarctation of the aorta. MRI also offers detailed data on flow volumes and velocities and has been used to evaluate wall shear stress.

Methods

Children with early repair of coarctation of the aorta (CoA) and age-matched controls underwent detailed cardiac MRI with evaluation of aortic compliance, flow and pulse wave delay. Shear stress was also calculated using a simple method.

Results

There was a significant difference in aortic arch compliance seen between the Subclavian Flap Repair subgroup and controls (p=0.02).

Conclusions

Normotensive children with early effective repair for CoA have reduced aortic compliance at the level of the aortic arch. This is associated with higher central blood pressure although no difference in aortic shear stress.

For more detailed information on this project, click here.

Velocity profile through the ascending aorta over the cardiac cycle and plot of flow vs time from trigger in the ascending and descending aorta used to calculate the pressure wave delay.

Evaluation of FLASH Ultrasound™ for Detection of Breast Cancer

FLASH Ultrasound™ of known breast cancer

Conventional Ultrasound of known breast cancer

FLASH Ultrasound™ of a tumour

Comventional Ultrasound of a tumour

This project was a collaboration between Medical Physics & Bioengineering University Hospitals Bristol and Weston NHS Foundation Trust, Innervision Medical Technologies Calgary, and North Bristol NHS Trust.

The objective of the clinical evaluation was to demonstrate the possibility of detecting breast cancer, prostate cancer and carotid artery disease using FLASH Ultrasound™ imaging and attribute analysis technology. FLASH Ultrasound™ imaging utilizes synthetic aperture ultrasound imaging technology to reconstruct images which are focused at all depths in both transmit and receive, allowing increased spatial and contrast image resolution compared to conventional ultrasound. The attribute analysis is based on techniques employed in Geophysics and Sonar in addition to recent advances in computational technology. By overlaying the attribute analysis on the FLASH Ultrasound™ images (similar to B-mode and Doppler in conventional ultrasound) this technology can provide additional information, such as speed of sound, to characterise tissue properties.

Scans were performed on a group of breast cancer patients undergoing adjuvant chemotherapy, outpatients attending a Trans-rectal Ultrasound Clinic and patients with suspected carotid artery disease attending a Vascular Studies Unit. The results were compared with conventional images where possible and with clinical results.

The initial results have been encouraging. The simplest processing in the system is used to create the localizing scans enabling real-time visualization of the anatomy and pathology of interest. The imaging results of the more intensive processing algorithms agree with conventional scan results.  Processing for the attribute analysis to characterize particular tissue types has created some results which seem to be specific for diseases, especially in the case of breast and prostate pathologies.

FLASH™ Ultrasound imaging and attribute analysis technology has the potential for patients to benefit from: earlier detection of disease, improved management and reduced complications following treatment.

We are planning further studies to evaluate the potential for real-time FLASH Ultrasound™ and attribute analysis to identify prostate cancer, breast micro-calcification and carotid plaques by comparative studies with biopsy samples.

If the ability to detect micro-calcifications is proven then FLASH ultrasound™ guided biopsy would be less costly than the current method (stereotactic x-ray guided biopsy) and the biopsy could be incorporated into an initial diagnostic ultrasound scan, reducing time to treatment and cost.

Measurement of Cerebral Vascular Reserve using Functional Magnetic Resonance Imaging

In healthy people, when the brain requires more oxygen and nutrients the blood vessels dilate and there is an increase in the volume of blood flowing to the brain. Cerebral vascular reserve (CVR) is a measure of this ability of the blood vessels supplying the brain to respond to increasing demand. In some people the cerebral vascular reserve is impaired and the blood supply does not increase when the brain requires more oxygen.

Assessment of CVR is thought to be clinically important; it could help identify patients at increased risk of stroke and determine the best course of treatment. One method currently used to measure CVR is to use radioactive tracers to measure the blood flow in the brain but this technique requires the use of expensive tracers and needs the patient to attend the hospital on two separate days. 

A technique called Blood-Oxygen-Level-Dependent functional MRI (fMRI BOLD) has been shown to measure changes in blood flow to the brain. We are investigating whether fMRI can measure CVR in place of the existing technique. It does not use radioactivity and can be completed during one scanning session. The patient is asked to lie in the scanner and to carry out a series of breath holds (for up to 20s) while being scanned. 

We undertook a pilot study in which 5 patients and 3 normal volunteers were scanned. The data showed that when analysising the patient population with breath-hold BOLD fMRI the data can be very different to the standard model, which could have implications for the accuracy of the analysis of this data in the future.

For more detail on the project, click here.

Figure 1 SPM8 analysis of fMRI BOLD in a healthy volunteer   Figure 2 Functional data overlaid on a structural MRI                                                                                                                     scan                                                                                                     

For more information, contact:

Sian.Curtis@UHBW.nhs.uk, Claire.Doody@NBT.nhs.uk

Synthetic Aperture Radar Detection of Breast Tumours

Introduction

A novel breast imaging technique has been developed based upon a synthetically-focussed but real-aperture multistatic radar and is known as MARIA (Multistatic Array processing for Radiowave Image Acquisition).

The technology was founded by Professor Ian Craddock (currently Professor, University of Bristol, and scientific project leader, heading the University's radar imaging group (www.bristol.ac.uk/engineering )) and Professor Alan Preece (previously Head of Biophysics Unit, Department of Medical Physics and Professor of Medical Physics, University of Bristol). Micrima (www.micrima.com), a spin-off company from the University of Bristol led by executive chairman Roy Johnson, are developing the radiowave radar technology for medical imaging applications.

The radiowave radar technology is non-invasive, non-ionising and inexpensive. It has undergone extensive validation in the laboratory and is now undergoing further clinical trials at Southmead Breast Care Centre, North Bristol NHS Trust (lead clinician, Dr Mike Shere) supported by researchers (clinical scientists) from the Department of Medical Physics and Bioengineering, University Hospitals Bristol and Weston NHS Foundation Trust.

Synthetic Aperture Radar

Breast tumours have an additional property that can distinguish them from normal and this is defined by the dielectric value.  This has two components - the dielectric constant which affects the velocity of propagation of radio waves and therefore their wavelength, and the conductivity which affects the rate of attenuation. In the microwave region this difference is quite large. Typically a tumour has a dielectric constant of 45-50 and a conductivity of 2S/m, whereas breast fat is 5-15 and 0.2-1S/m respectively but with considerable range.  Normal glandular tissue is intermediate.

What is the purpose of the study?

The purpose of the study is to clinically evaluate the latest modifications and improvements to MARIA equipment hardware, software and data analysis techniques against conventional imaging modalities (x-ray mammograms, ultrasound and MRI) used in the diagnosis of breast disease in a cohort of symptomatic patients.

Refinement of a thin wafer detection system for real-time 2D verification of modulated radiotherapy.

Funded by UH Bristol NIHR Research Capability Funding Call.  Started Jan 2013.

Clinical scientists and radiographers at BHOC, and academics from Bristol and Swansea universities, have been developing a novel radiation detector device to reduce the risks of mistreatments during radiotherapy. 

Advances in the way radiation is delivered to patients to treat cancer mean that tumours can be much more accurately targeted, greatly reducing the damage from radiation to surrounding tissue and sensitive organs. Finely engineered components in the treatment machine shape the radiation field directed at the tumour. 

A consequence of this complex technology is that changes to the radiation beam cannot be easily recognised and if faults occur, they may not be immediately spotted. This can result in mistreatments if radiation beam components are misaligned. 

The project team offers expertise in the fabrication of radiation detectors and the modelling of clinical radiation equipment. We have developed a novel solution using a detector based on very thin silicon camera systems which does not interfere with the radiation beam. We have been able to prove this concept with a static system but now need to extend the work to dynamic treatments and a range of machines.  The aim is also to speed up data collection and validate the system in real time.  Ultimately this will provide the radiographer with an instantaneous real time image of the beam as it is delivered. Any errors can then be corrected before adversely affecting the patient.

This project builds on developments from a previous NIHR i4i-funded project led by Mrs Cathy Hall (UH Bristol) and Dr Jaap Velthuis (University of Bristol) in partnership with Prof Richard Hugtenburg (University of Swansea). This interim grant has enabled us to bid successfully for further NIHR i4i funding.  See NIHR i4i TRAPS project.