Magnetic resonance imaging in acute head injury.

Using cardiorespiratory monitoring and support equipment compatible with a low field (0.15 T) system, magnetic resonance imaging (MRI) of patients suffering acute head injuries proved to be both feasible and safe. An abnormality was demonstrated by magnetic resonance imaging in 46 of 50 patients examined within 7 days of head injury using T2 weighted (SE2200/80) and T1 weighted (IR2000/600/40) multislice sequences. IN contrast, computed tomography (CT) demonstrated abnormalities in only 31 of the 50 patients. Intracranial extracerebral space-occupying collections of blood were well shown by magnetic resonance imaging which provided especially clear definition in the posterior fossa, subtemporal and subfrontal regions. Magnetic resonance imaging was more sensitive to cerebral abnormalities associated with traumatic unconsciousness and detected parenchymal lesions both in patients in coma and in those who had lost consciousness for only a few minutes. Lesions seen with MRI but not with CT included non-haemorrhagic contusions and abnormalities thought to reflect shearing injuries of white matter and intracerebral vessels. Magnetic resonance imaging is an effective alternative to CT; the additional information it can provide should be valuable in increasing the understanding of the early effects and late consequences of a head injury.

Accuracy of stereotaxic localisation using MRI and CT.

The accuracy of stereotaxic coordinates determined using the Leksell apparatus with CT and MRI was investigated using an Agar filled head phantom. Both imaging techniques were found to produce an accuracy of better than 2 mm with the exception of the Z coordinate as measured by CT (2.3 mm). This latter error is greater because of the 3 mm slice width used. Direct coronal views were used to determine Z more accurately using MRI. The measurement procedures are described and it is shown that the Leksell system of using orthogonal coordinates enables the scaling of images, which is particularly necessary with MRI, to be done easily.

Brain lesions detected by magnetic resonance imaging in mild and severe head injuries.

50 patients were studied by magnetic resonance imaging (MRI) within one week of a head injury. Abnormalities indicating primary brain damage were found in 46 patients, almost twice as many as with computed tomography. Cortical contusions were the most common finding, irrespective of the effect of injury on the level of consciousness. Intracerebral lesions were seen only in patients who had lost consciousness and were present in 29 of 42 patients whose consciousness was still impaired on arrival at hospital. Lesions in the deep white-matter of the cerebral hemispheres were seen in 15 patients; they were significantly more frequent in patients in coma but were also seen in patients who had lost consciousness for no more than 5 min. The findings indicate that lesions in the cerebral hemispheres may be the primary factor in traumatic unconsciousness. MRI studies may also clarify the sequelae of head injuries.

Clinical evaluation of two methods of subdural pressure monitoring.

Recordings from two different types of subdural pressure monitor with simultaneous intraventricular pressure (IVP) tracings are compared in 20 head-injured patients. In the first 10 patients a fluid-filled catheter was placed subdurally and connected to an external transducer, and in the second 10 the Gaeltec model ICT/b solid state miniature transducer was used. The latter system has the advantage that both zero and calibration checks can be carried out after insertion. Only 44% of the fluid-filled catheter readings corresponded with IVP in series of 10-mm Hg ranges, while 53% of readings were lower; this tendency was more marked at higher pressures. With the Gaeltec transducer, 72% of subdural pressure readings corresponded with IVP, while only 9% were lower and 19% were higher than IVP. The differences may have been due to technical causes or to true pressure differentials. The subdural catheter appears too unreliable for routine clinical use, but the Gaeltec transducer may be a satisfactory alternative to ventricular pressure monitoring.

Analysis of the cerebrospinal fluid pulse wave in intracranial pressure.

The configuration of the intracranial pressure (ICP) pulse wave represents a complex sum of various components. Amplitude variations of an isolated component might reflect changes in a specific intracranial structure. Fifteen awake patients suffering from hydrocephalus, benign intracranial hypertension, or head injury underwent ICP monitoring through a ventricular catheter and were subjected to three standardized maneuvers to alter the intracranial dynamics: head elevation, voluntary hyperventilation, and cerebrospinal fluid (CSF) withdrawal. A 12 degrees head elevation and fractionated CSF withdrawal caused a mild ICP drop and a proportionate amplitude reduction of all the wave components. Voluntary hyperventilation caused a comparable fall in ICP, and a disproportionate reduction in the amplitude of the wave components, especially the P2 component. It is postulated that the decrease in amplitude of the P2 component reflects the reduction of the cerebral bulk caused by hyperventilation. Head elevation and CSF withdrawal caused a decrease of global ICP but no specific changes in any intracranial structure, and consequently the configuration of the pulse wave remained unchanged. The establishment of relationships between anatomical substrate and particular wave components is promising since potentially it could be useful for monitoring conditions such as vasoparalysis, impaired cerebrovascular reactivity, and cerebral edema.

Comparison of cerebral blood flow after venesection of bronchitic secondary polycythaemic and primary polycythaemic patients.

Cerebral blood flow was measured before and after lowering of haematocrit in four patients with primary polycythaemia and in nine with polycythaemia secondary to chronic obstructive airways disease. Cerebral blood flow values in each group were abnormally low to a similar degree at the start of the study and the degree of rise in cerebral blood flow per unit fall in haematocrit after venesection also was similar in each. Oxygen delivery fell despite increased cerebral blood flow and symptomatic benefit was infrequent. In male secondary polycythaemic patients rise in cerebral blood flow was not associated with any improvement in hypothalamo-pituitary-testicular function which we had previously noted to be suppressed in such hypoxic subjects. Our findings suggest viscosity changes rather than alteration in blood oxygen carriage to be responsible for cerebral blood flow improvement. It is concluded that therapeutic venesection in such patients should be applied with caution.

A clinical comparison of subdural screw pressure measurements with ventricular pressure.

Simultaneous recordings of intracranial pressure (ICP) from a single-lumen subdural screw and a ventricular catheter were compared in 10 patients with severe head injury. Forty-one percent of the readings corresponded within the same 10 mm Hg ranges, while 13% of the screw pressure measurements were higher and 46% were lower than the associated ventricular catheter measurements. In 10 other patients, also with severe head injury, pressure measurements obtained with the Leeds-type screw were similarly compared with ventricular fluid pressure. Fifty-eight percent of the dual pressure readings corresponded, while 15% of the screw measurements were higher and 27% were lower than the ventricular fluid pressure, within 10-mm Hg ranges. It is concluded that subdural screws may give unreliable results, particularly by underestimating the occurrence of high ICP.

Cerebral blood flow and intelligence rating in persons over 90 years old.

Cerebral blood flow (CBF) and intellectual rating scale (IRS) measurements were carried out in 54 subjects over the age of 90. Two successive measurements of CBF by the xenon-133 inhalation method, 20 min apart, were made in 38 of these persons under the same conditions in order to measure the precision (repeatability) of the CBF technique on this subject category. A statistically significant lower mean cerebral blood flow was found for this over-90-year-old group compared to young adults. The subjects were divided into subgroups according to their IRS score from normal to severely demented. Resting CBF in the various IRS groups did not differ significantly. However at low IRS values there was much less variability between successive CBF measurements in the same individual suggesting failing vasomotor tone with senile dementia.

Atraumatic xenon-133 techniques and the measurement of cerebral blood flow in the investigation room, operating theatre and intensive care unit.

The ideal CBF measurement technique should be completely atraumatic, the investigation time should be short, and repeated regional measurements, having a precision such that clinically significant CBF changes can be detected, should be possible. The Glasgow methods have been designed around these principles. The inhalation technique has been applied to CBF measurement during trial carotid artery compression, drug assessment, paraplegia and polycythaemia. The intravenous injection technique has proved useful in the investigation of patients with severe head injuries and raised intracranial pressure and in indicating a suitable level of hypotension during aneurysm surgery.

Measurement of CBF and carotid artery pressure compared with cerebral angiography in assessing collateral blood supply after carotid ligation.

Angiographic assessment of collateral circulation to the brain at the circle of Willis was compared with measurements of cerebral blood flow (CBF) and internal carotid artery pressure during temporary carotid clamping in the prediction of tolerance of unilateral carotid ligation as treatment for intracranial carotid aneurysms in 92 patients. From CBF studies it was predicted that a substantial number of patients (27%) would suffer severe cerebral ischemia if carotid ligation were carried out. No single angiographic feature provided this predictive information. Bilateral fetal type of posterior communication arteries were associated with significantly lower carotid artery back pressure on temporary carotid occlusion, and unilateral absence of posterior communicating arteries was related to llower CBF, but neither feature was associated with a signifiant reduction in the rate of successful carotid ligation. We believe that preliminary percutaneous digital corotid compression with electroencephalographic monitoring, followed by intraoperative measurement of the change in regional CBF and internal carotid artery pressure during temporary carotid clamping provides a safe method of selecting patients for carotid ligation. Carotid angiography with or without contralateral carotid compression is of little value in this respect.

The construction and use of nomograms for cerebral blood flow calculation using a 133Xe inhalation technique.

Measurement of cerebral blood flow (CBF) using a 133Xe inhalation technique requires monitoring the clearance rate of the radioisotope from the head using externally situated detectors and also from arterial blood using a detector to monitor the expired air activity. The end-tidal concentration function is assumed to be proportional to the arterial concentration function and this has to be deconvoluted from the clearance functions obtained from the head to enable CBF to be calculated. A digital computer is generally considered to be essential for this. In this paper a procedure using three-dimensional nomograms is derived and tested. It is shown that results obtained using the nomograms do not differ significantly from results obtained using a full deconvolution procedure, and so it is not essential to use a computer to calculate CBF by the inhalation technique.

Two minute slope inhalation technique for cerebral blood flow measurement in man. 1. Method.

The two minute slope method of measuring cerebral blood flow (CBF) by inhalation of 133Xe is described. It requires the subject to remain still for only two minutes and is thus applicable to a wide variety of patients and to investigations involving brief physiological stimuli. The influence of extracerebral blood flow on CBF calculated by this method has been studied. Results from the two minute slope inhalation method using two minutes of data correlate well with those obtained by carotid injection using either two minutes or 10 minutes of data.

Two minute slope inhalation technique for cerebral blood flow measurement in man. 2. Clinical appraisal.

The two minute slope technique for measuring CBF was devised primarily to study the response of the cerebral circulation to physiological stimuli. In this paper, measurements of the precision of the technique when applied to various groups of people are described, and measurements on normal subjects of the global and regional CBF changes in response to hyperventilation and hypercapnia are presented. It is shown that CBF measured using this technique during percutaneous carotid compression may prove useful in the prediction of cerebral ischaemia in patients who are candidates for carotid ligation.

Spinal cord blood flow measured by a hydrogen clearance technique.

Spinal cord blood flow (SCBF) has been measured in segments of the thoracolumbar cord of dogs using the hydrogen clearance technique. Clearances were recorded and flows calculated from electrodes placed in grey and white matter. The position of the recording electrodes was marked by diathermy and confirmed in each experiment. The SCBF in the white matter for 82 clearances was 13.7+/-4.5 ml/100 g/min using pentobarbitone anaesthesia. In the grey matter both monoexponential and biexponential clearances were recorded from electrodes placed in grey matter. There was no difference in flows calculated from the monoexponentail and slow components. SCBF from the slow components or monoexponentials was 12.0+/-4.5 ml/100g/min. The flow from the fast component was 69+/-11 ml/100 g/min. with pentobarbitone anaesthesia and 97.5+/-32.9 ml/100g/min with alpha-chloralopse anaesthesia. The flow calculated from the fast component did not correlate to changes of PaCO2. The slow component of any biexponential clearances was used to calculate flows from electrodes placed in the grey matter. There was no significant difference between flows from the grey matter (calculated from the slow component) and the white matter. Simultaneously recorded cortical and sub-cortical -lows were higher than in spinal grey and white matter. There was considerable variation in flow from animal to animal. The area of spinal grey matter is small and surrounded by white matter and the flow recorded from electrodes placed in grey matter is probably the average SCBF representing a mixture of grey and white flow. This will arise because of the rapid diffusibility of hydrogen gas between the tissues. It is therefore difficult to ascribe the flow from a centrally placed cord electrode to a definite anatomical compartment.

Raised intracranial pressure and cerebral blood flow. 5. Effects of episodic intracranial pressure waves in primates.

The effects of episodic waves of intracranial pressure on cerebral blood flow were studied in primates. Six pressure waves each of 20 minutes' duration and ranging from 50 to 100 mmHg in magnitude were induced in baboons, at intervals of 30 minutes, in an attempt to simulate clinical plateau waves. With pressure waves up to 75 mmHg, cerebral blood flow remained at control levels despite falling cerebral perfusion pressures. Between the initial pressure waves a marked hyperaemia developed, with cerebral blood flow increasing by as much as 100%, and this appeared to be a means whereby adequate flow was maintained during pressure waves. Later pressure waves, up to 100 mmHg, eventually reduced blood flow below control levels, although moderately high flows were maintained during periods of very low perfusion pressure. Brain metabolism was affected by eht episodic pressure waves, although no consistent change was seen.