56 2011
IMAGING & ONCOLOGY
These are ambitious goals, but will enable prevention of subsequent stroke in cases of TIA, and timely treatment in cases of stroke, reducing the risk of subsequent death and disability. In terms of changes to current service provision, the management of TIAs may represent a more significant challenge than the urgent response to stroke, particularly out of hours and at weekends.
IMAGING WORKLOAD IMPLICATIONS In 2008, the Department of Health published ‘Implementing the national stroke strategy, an imaging guide’7
. This document, produced by a large number of
stakeholders involved in imaging, estimated the expected workload for imaging departments. Within this document, there are calculations on the impact this would have by estimating the number of scans required for a given population. The figures given per 500,000 population are:
For TIAs: • Approximately 30 patients a week presenting with TIAs. • 50% will require brain imaging (66% within 24 hrs). • 80% will require carotid imaging (66% within 24 hrs).
Thus anticipated imaging during the week, 12 MRI/MRA brain and 10 carotid imaging. During the weekend, three MRI/MRA brain and two carotid imaging.
For stroke: • Approximately 25 patients a week presenting with strokes. • Almost 100% will require brain imaging (50% within one hour). • 10-20% of urgent cases will require additional imaging within 24 hours, eg MRI.
Thus anticipated imaging during the week, 15-17 brain CT and 3-4 MRI. During the weekend, 7-9 CTs with 1-2 a month requiring MRI.
This is a significant change from previous management. Although most stroke patients would have previously had some form of brain imaging (usually CT), the new guidelines require the scans within one hour, if urgent (50%), and within 24 hours otherwise. This requires departmental flexibility to accommodate scans at short notice. The implications in TIAs is perhaps more significant because most patients are not, at present, having MRI scans. This may add significantly more than 10 per cent to the workload of a district general hospital MRI scanner, compounding the already fully stretched national MRI capacity.
CURRENT PROVISION FOR TREATMENT Thrombolysis is available in 88 per cent of acute trusts, (RCP audit May 2010) but only 50 per cent are 24/78
. Nevertheless, the availability of thrombolysis has increased significantly over the past two years.
CEA services are variable, with very few acute trusts offering a full 48-hour service. CEA within two weeks is achieved more frequently, but even this timescale is by no means universal. The Royal College of Vascular Surgeons remains committed to trying to improve CEA availability.
MONITORING All primary care trusts will be expected to collect data relevant to imaging, which includes the following: 1. Treatment of higher risk individuals with TIA, defined by a score of 4 or more on the ABCD2 system1
. They will be expected to provide data on the proportion of these patients who are scanned and treated within 24 hours of symptom onset.
2. For lower risk TIA, the same applies but for a seven day period. 3. Percentage of TIA patients with confirmed carotid stenosis receiving carotid intervention within 48 hours. Percentage of stroke patients scanned within one hour and 24 hours.
MOVING FORWARD, NEWER TECHNIQUES AND USAGE Mechanical clot retrieval Pilot trials suggest benefit from intravenous thrombolysis and endovascular mechanical clot retrieval/aspiration, using mechanical devices to dispose of large proximal clot burdens. This can be combined with the ability of lytics to initiate therapy early, or clean up smaller occlusions in distal arteries not accessible to mechanical attack9
. At
present, this is available only in major centres, usually performed by interventional neuroradiologists. Use of the ‘hub and spoke model’ and networking across stroke services should lead to an increase in the use of this technique.
CT perfusion scanning CT perfusion is used widely already, although its role in the acute stroke setting is still under debate. Recent publicity in the United States has muddied the waters because patients having multiple CT brain perfusion scans suffered radiation burns and local hair loss. These reports reached the UK lay press. Nevertheless, the advantage in assessing objectively the ‘penumbra’ is, at present, being used particularly to assess those patients in whom the timing of onset of symptoms is unclear, eg the ‘wake up strokes’. The additional information gained by the concurrent acquisition of a CT cerebral angiogram is helpful in some centres for assessment of arterial occlusion, prior to intra-arterial mechanical clot retrieval.
Carotid imaging During working hours, most carotid imaging is performed using ultrasound, either by sonographers or vascular scientists. However, both CT angiography and MRA of the carotid arteries provide accurate assessment of carotid stenosis. There are issues regarding training both to acquire and to report CT and MRA images, but the availability of both these scans out of hours and at weekends may mean an increase in their usage. Indeed, this is already happening at a number of centres.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72