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4-page summary in Adobe Acrobat format (suitable for printing) Health Technology Assessment 2002; Vol. 6: No. 7
Executive summary
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E Berry1*
S Kelly1
ME Westwood1
LM Davies2
MJ Gough3
JM Bamford4
JFM Meaney5
CM Airey6
J Cullingworth5
M Barbieri2
A Jackson7
MA Smith1
1Academic Unit of Medical Physics and Centre of Medical Imaging Research, University of Leeds, UK
2 Centre for Health Economics, University of York, UK
3 Department of Vascular Surgery, Leeds General Infirmary, UK
4 Department of Neurology, St. James’s Hospital, Leeds, UK
5 Department of Radiology, Leeds General Infirmary, UK
6 Division of Public Health, Nuffield Institute for Health, University of Leeds, UK
7 Diagnostic Radiology, University of Manchester, UK
* Corresponding author
The principal manifestations of carotid and peripheral atherosclerosis, respectively, include transient ischaemic attack and stroke, and lower limb arterio-occlusive disease resulting in intermittent claudication (pain on walking), ischaemic rest pain, ulceration or gangrene. The total costs to the NHS of arterial and venous disease, in hospital and primary care, exceed £350 million; the total costs of stroke have been estimated as substantially higher, at 5.8% of total expenditure.
Clinical decision-making relies on evaluation of the vessels in terms of the degree of stenosis, or narrowing. Magnetic resonance angiography (MRA) is a technique for imaging blood vessels that contain flowing blood. It can be performed on most magnetic resonance scanners installed in hospitals today, and represents an alternative to conventional angiographic techniques using X-rays (digital subtraction angiography (DSA)), or more recent imaging developments, including ultrasound. In this review the use of contrast-enhanced MRA and two-dimensional (2D) and three-dimensional (3D) time-of-flight (TOF) MRA for presurgical assessment in carotid artery disease and in peripheral vascular disease is considered.
Studies of the diagnostic performance of MRA in the relevant clinical conditions and performed on humans were included with two provisos: that sufficient data were reported for the construction of a 2 x 2 contingency table, and that application-specific inclusion criteria were satisfied. Non-English-language studies were included. Studies reporting cost data were included, providing resource use and costs for the UK setting were reported separately, and providing the study did not use expert opinion or charge data to estimate costs.
Checklists that covered study design, patient characteristics, technical details and potential biases in study execution were completed independently by two reviewers. Consensus was reached on any disagreements. One reviewer, who worked with another where difficulty arose, extracted results on diagnostic performance. Summaries were written to describe each article. Cost data were extracted and summarised by two team members.
Summary receiver operating characteristic methods were used to combine the results of diagnostic performance studies, grouped by MRA technique and diagnostic threshold. The thresholds used were:
Study validity was investigated using a multiple linear regression analysis. Overall event rates were calculated by pooling patient results from the included studies. A decision analytic model was used to combine information from the literature and cost estimates, in order to determine the relative cost-effectiveness of MRA and DSA in the two clinical applications. The analysis was performed from the perspectives of the healthcare purchaser and clinician. Sensitivity analysis was performed.
Ten articles on carotid artery stenosis satisfied all the inclusion criteria and a further 24 satisfied at least four inclusion criteria. There were too few articles on the latest contrast-enhanced techniques for quantitative synthesis, but the results appear better than those for 2D and 3D TOF methods. The TOF methods are highly accurate for detecting occlusion and 70–99% stenoses, but are less accurate for 50–99% stenoses. The decision analytic model showed that over 10 years following its use, MRA is expected to cost £194 less than DSA, with no difference in expected quality-adjusted life-years (QALYs). Providing the equipment is used at more than 10% of capacity, MRA is associated with lower expected costs than DSA.
Twenty articles on peripheral vascular disease satisfied all the inclusion criteria. Both 2D TOF and contrast-enhanced MRA are highly accurate for distinguishing 0–49% from 50–100% stenoses. The contrast-enhanced techniques show a non-significant trend for improved performance over 2D TOF MRA. The decision analytic model showed that there is no difference in expected QALYs for MRA and DSA. If the equipment is used at under 100% of capacity, 2D TOF MRA is associated with higher expected costs than DSA, but contrast-enhanced MRA has lower expected costs.
In carotid artery disease, 2D and 3D TOF MRA techniques are accurate for identifying both occlusions and 70–99% stenoses as defined by conventional angiography. The evidence does not support their use for identifying 50–99% stenoses. If the utilisation rate for an MRA system to evaluate all patients (with and without carotid artery disease) is greater than 10%, then MRA is likely to be a cost-effective option.
In peripheral vascular disease the evidence supports the use of 2D TOF and contrast-enhanced MRA techniques for identifying occlusions and 50–100% stenoses. If both DSA and MRA are already available in the local setting, then MRA is more cost-effective than DSA, especially if contrast-enhanced MRA is available.
The conclusions about cost-effectiveness are valid only for high-quality diagnostic studies. Such examinations can only be performed following training and adequate experience. Consequently, there is a case for guidelines, training and accreditation schemes to be established by the relevant professional bodies.
Berry E, Kelly S, Westwood ME, Davies LM, Gough MJ, Bamford JM, et al. The cost-effectiveness of magnetic resonance angiography for carotid artery stenosis and peripheral vascular disease: a systematic review. Health Technol Assess 2002;6(7).
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The research reported in this monograph was funded as project number 97/13/04.
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