Rapid neuroimaging of acute stroke patients

Stroke patients can respond well if rapid diagnosis is followed by prompt and appropriate therapy. For example in ischaemic stroke timely administration of thromobolytic or “clot-busting drugs” can prevent the progression of symptoms from transient to permanent. Delays in diagnosis can however lead to irreversible cerebral damage. The principal diagnostic challenge in overall stroke management is to differentiate brain ischaemic attacks from haemorrhages and stroke-like disorders. While timely non-contrast CT imaging distinguishes between haemorrhagic and ischaemic stroke, many hospitals cannot offer continuously available CT scanning in the radiology department. A dedicated, head/neck scanner in the ER facilitates rapid differential stroke diagnosis.
by Dr David B. Weinreb

Stroke is the third most frequent cause of mortality after ischaemic heart disease and cancer, and the primary cause of disability in adults worldwide. In 2005, there were an estimated 62 million stroke survivors. Over 15 million people suffer a stroke each year and of these, approximately five million will die as a result, and another five million will be permanently disabled. One of the most important challenge facing physicians globally is to reduce the unacceptable burden of stroke.

Prompt differential diagnosis is essential, but achieving rapid imaging in the Emergency Room (ER) is challenging, both for small community hospitals and large academic centres. There are numerous, frequently-encountered clinical scenarios for which there is an urgent need to briskly transport patients to the radiology suite: suspected intracranial haemorrhage, pulmonary emboli or ruptured aneurysms. Delays in obtaining the appropriate diagnostic imaging study create delays in correct management. This is particularly significant for patients presenting to the ER with signs of acute stroke.

Thrombolytic, or “clot-busting,” drugs offer tremendous hope to stroke patients, breaking apart the clots that deprive the brain of oxygen, preventing symptoms from progressing from transient to permanent. However, thrombolytic agents may be contraindicated in many patients. First and foremost, clinical guidelines dictate that thrombolytic drugs be administered within three hours of symptom onset. If administered after this three-hour window, the potential risks of bleeding complications tend to outweigh the benefits. For example, in about 83% of acute stroke patients their symptoms are secondary to a clot starving the brain of oxygen [1]. For the remaining 17% the stroke may be consequent to a site of haemorrhage in the brain [1]. In all such cases, administration of a clot-busting drug will exacerbate the hemorrhage. It is crucial to rapidly image such patients and “triage” them accordingly: those with oxygen-depriving clots may indeed be candidates for thrombolytic drugs; haemorrhage within the brain is an absolute
contraindication to such therapy.

Non-contrast CT imaging
The first step in the evaluation of acute stroke patients is to distinguish between patients whose symptoms are due to bleeding (haemorrhagic stroke) and those patients presenting with stroke due to clots (ischaemic stroke). This can be achieved with non-contrast CT imaging [Figure 1a and 1b]. Within the few hours of the onset of a haemorrhagic stroke, the non-contrast CT scan will identify the presence of haemorrhage. These patients require close neurological monitoring and possible neurovascular/neurosurgical interventions to control the bleeding.
By comparison, within the first hours of an ischaemic stroke, non-contrast CT imaging may likely be completely normal: the clot is barricading the flow of oxygen-rich blood to the brain, but it is too early to see any changes in the brain apparent on CT imaging. Generally, greater than 24 hours after the onset of symptoms, repeat CT imaging will demonstrate areas of low attenuation, corresponding to brain territory that has been deprived of blood flow.

Non-contrast CT imaging should therefore be performed as briskly as possible in patients with suspected acute stroke. The National Institute of Neurological Disorders and Stroke (NINDS) urges that CT imaging be completed within 25 minutes of the patient arriving in the ER; the images should be interpreted within 45 minutes [2]. For various reasons, compliance with these time guidelines may be more easily attained in large academic centres. Specifically, these larger institutions may have a stroke team consisting a specialised nurse and stroke neurologist on-call to evaluate patients in the ER. Additionally, the radiology department may have continuously available CT scanning in the ER, staffed around the clock by teams of technologists.
However, the situation may be quite different in smaller community hospitals, and such differences have constructed barriers to ideal care. First, many community hospitals may not have a CT scanner in the ER; their imaging facilities may be located in another building and, in many cases, off-site. Additionally, the CT department may not be staffed 24 hours a day. These obstacles to the “25-minutes to CT” guideline represents challenges facing smaller community hospitals. This is particularly and painfully relevant given that the overwhelming majority of stroke patients initially present to community hospital ERs.

Use of a dedicated head/neck CT scanner
First, one creative solution is a dedicated head/neck CT scanner, stationed in the ER, ready at a moment’s notice for an arriving stroke patient. One manufacturer, NeuroLogica Corporation in Massachusetts, has developed a light-weight (700-lb), portable 8-slice scanner [Figure 2]. Designed specifically for head imaging, this scanner is stored in the ER, eliminating the need for stroke patients to be transported to the radiology suite. In many of the community hospitals where this novel scanner is currently operating, it has helped clinicians achieve the “25-minute” guideline [3].

A recent investigation has explored the clinical utility of the portable CT scanner for ER patients [3]. The study was conducted in the 16-bed ER of Salem Hospital/North Shore Medical Center (Salem, Massachusetts). At Salem Hospital, it typically took 25-35 minutes from the time of initial arrival at the ER door until the CT scan was completed. This delay in transporting the patient to the radiology suite for CT imaging was one of the several factors that slowed the entire process of clinically assessing patients presenting with an acute ischaemic stroke. Thus, interventions were necessary to provide more rapid diagnostic imaging for ER patients.
Following the implementation of a dedicated scanner in the ER, these times was drastically reduced to less than 17 minutes; a large percent of ER stroke patients were imaged fewer than 12 minutes [Figure 3]. These preliminary results suggest that increasing the availability of CT in community or rural hospitals may have a tremendously positive impact on the ability to these hospitals to more effectively care for acute stroke patients.

In summary, providing rapid diagnostic imaging when and where it is needed the most is an enormous challenge. Nowhere is this challenge more apparent than in community hospitals, faced with the arrival of a stroke patient within the three hour period for thrombolytic interventions. The emergence of new technologies is helping to surmount this challenge, though new approaches and strategies at the community level are still needed.