Journal ofNeurology, Neurosurgery, and Psychiatry, 1972, 35, 912-918 Two-dimensional echoencephalography with electronic sector scanning Clinical experiences with a new method H. A. C. KAMPHUISEN, J. C. SOMER, AND W. A. OOSTERBAAN Department of Clinical Neurophysiology, University of Utrecht, and the Institute of Medical Physics T.N.O., Utrecht, The Netherlands SUMMARY A new form of ultrasound diagnostic possibility is presented (the electroscan). The basic principles of this two dimensional method are described. Special attention is given to the probe consisting of an array of 21 elements of piezo-electric material. The results of this method in four patients are discussed (meningioma, arteriovenous aneurysm, subdural haematoma, and a baby with hydrocephalus). The baby with hydrocephalus showed diagnostic problems which could be under- stood from the pneumoencephalographic findings. The electroscan method seems to offer good possibilities for the diagnosis of brain lesions, ifthese have a consistency different from that of normal brain tissue. Conventional echoencephalography is based on difficulty from an echo answering from a real the pulse-echo method, in which a transducer layer, as would be possible in a two-dimensional transmits short ultrasound pulses, the echoes of scanning system. which are received back during the intervals. These echoes are visualized as vertical excursions on an oscilloscope-screen, while the position on ELECTRONIC SCANNING PRINCIPLE the screen is a measure for the distance at which (Somer, 1968) the reflecting structure is situated. The direction Two-dimensional scanning for obtaining cross- of the emitted ultrasound pulses is always per- sectional pictures can be performed both mech- pendicular to the surface of the probe and thus it anically and electronically. The mechanical B- can be changed only by moving the probe. The scan and compound scan do not provide the poss- essential advantage of this so-called A-scan ibility of instantaneous and continuous pictures method is that the repetition-frequency of the and are not suited for searching for the optimal pulses can be so high as to allow one to visualize echo-pattern. An electronic scanning system may the echo-pattern on the screen as a practically overcome these defects, whereas it has all the instantaneous and continuous picture. Slight advantages of the cross-sectional display. variations in the position of the transducer cause The Research Group of Ultrasound-diag- variations in the echo-pattern, so that a search nostics of the Institute of Medical Physics can be made for the optimally interpretable T.N.O. in Utrecht has developed such an echo-pattern, because the oscilloscope-screen electronic scanning system, the so-called 'electro- can be observed continuously for the best pic- scan'. Both a mechanical compound scan and ture. this electroscan-machine are in use now at the The essential disadvantage is that only one EEG department of the University Hospital in unidirectional exploration in depth can be made Utrecht. In this communication only the elect- and that simultaneous multidirectional explora- ronic scanning method is discussed. tions are impossible. Because of this, a random Publications in the field of radar and sonar echo sometimes may be distinguished with induced us several years ago to develop an 912 Two-dimensional echoencephalography with electronic sector scanning 913 FIG. la. Construction of the multiple 'array' with 21 separate elements. direction of propagation /~~~~~~~~~ T T TqTTT T;TT TTTTT n_21 FI./b rnilshort wavefba ( omto h iecino hc a evre lcrnclyi oscillator time delaiy C~~ ~~~-~~ cir:.uitIIt I t I J_from trigger pulse oscillator /I.Ib rnil f emfraintedreto fwihcnblcrncl,vre 914 H. A. C. Kamphuisen, J. C. Somer, and W. A. Oosterbaan electronic sector scan system for diagnostic while the probe is stationary, and again a search purposes and this resulted in the construction of a can be made for an optimal representation. The prototype which is now used experimentally by disadvantage of the unidirectional exploration, us. This system is equipped with a probe of however, has now been overcome and larger special construction, an 'array' consisting of a parts of structures can be depicted. series of 21 small elements, which can be excited individually. Figure la shows this array with elements of piezo-electric material, spaced CLINICAL INVESTIGATION half a wavelength apart. Each of these elements The well known unidirectional A-scan echo- can convert a short electrical pulse into a short encephalography has proved in the last decade mechanical oscillation and thus produce an to be of great value in clinical neurological ultrasound impulse with an almost circular wave- investigation. The method provides information front. which is almost exclusively limited to midline Figure b shows that each element is con- echo structures. Occasionally some information nected to an electrical source for exciting the is obtained concerning the width of a ventricle element. This source is connected to a starting but in most cases certainty on this is obtained pulse generator by means of a delay circuit. This only by means of pneumoencephalography. delay circuit causes the corresponding element The two-dimensional electronic sector scan to be excited at a required time after the starting echoencephalography (electroscan) makes it pulse. possible to obtain clear information concerning The delay circuits are adjusted in such a way spatial relations inside the skull. The pictures that the first element is excited first, the second obtained by the electroscan are usually complex afterwards, and the following elements at sub- and not easily interpreted. The midline structures sequent equal time intervals, and reversed. At the are easily recognized and their location may be moment that the last element is excited the wave measured accurately, but for this determination front of the first has travelled over a certain conventional A-scan echoencephalography is distance, the wave front of the second element more convenient. The electroscan has proved to over a shorter distance, etc. According to be useful in particular for the study of abnormal Huygens's principle, all wave fronts together structures in a cerebral hemisphere. The evalua- build up a resultant flat wave front with a certain tion of the results is carried out afterwards on the angle to the probe. The angle of this resultant basis of measurements on photographs made wave front depends on the time intervals be- from the TV screen. Usually 24 to 30 photo- tween the subsequent excitations. The direction graphs are taken in each case. These pictures are of the beam is perpendicular to the wave front obtained from probe situations on homologous and therefore also depends on the time delays places on the right and left sides of the skull. The between the subsequent excitations. Since the probe is placed either in a horizontal or a delays are obtained electronically, they can be vertical direction. varied very rapidly and thus the direction of the Some results, obtained in a small series of beam can be changed quickly. By varying the patients in whom the echo pictures could be delays systematically, a sector can be scanned verified anatomically, will be described. repetitively. In this way a sector of 90° can be scanned in about 30 different directions (at 3° CASE 1 steps) whereby a repetition rate of 30 scans/sec A woman, aged 55 years, had since her youth com- is achieved easily. When receiving the echoes, plained of headaches, localized particularly in the variable delays are again applied in order that posterior part of the head. Lately, vision had deteriorated. The woman was obese (103 kg), the directions of reception and transmission are loquacious, and somewhat confused. The blood always the same. On the screen echoes are pressure was 220/110 mm Hg. The ocular fundi visualized as variations of brightness of the spot. showed hypertensive change, and, on the right side, Because of the scanning rate of 30 scans/sec papilloedema was noted. the advantage of the A-scan is retained and an The left pupil was slightly wider than the right. instantaneous and continuous picture appears There was slight bilateral exophthalmos and a slight Two-dimensional echoencephalogragphy with electronic sector scanning 915 FIG. 2. Case 1. Picture of a horizontal electroscan probe left temporal. In the right hemisphere (arrow) there is a massive shadow which was interpreted as pathological. At operation a large meningioma was encountered in this area and subsequently removed. ptosis on the left side. No other neurological ab- revealed this mass to be a large meningioma in the normalities were encountered. Elsewhere the dia- right fronto-basal area. The meningioma was nosis of pituitary tumour had been considered. removed. The electroencephalogram (EEG) was markedly with hypofunctional abnormal and asymmetrical, CASE 2 abnormalities dominating in the right frontal areas spreading over the entire hemisphere and to the left In a man aged 34 years cerebral angiography had frontal area. revealed an unusually large arteriovenous aneurysm. Conventional echoencephalography showed a The location of this aneurysm was not known to the displacement of midline structures to the left side, electroscan investigator at the time of the examina- amounting to 5%0 in the temporocentral areas. tion. When the probe was placed on the right The electroscan investigation was carried out by frontal area in this patient, unequivocal echo com- an investigator who was kept ignorant of information plexes were noted in the left frontal area. When the described above. When the probe was placed on the probe was placed on the right central area con- left temporal and left central areas a massive spicuous shadows were also seen in the left fronto- 'shadow' was observed in the right frontotemporal central areas. When the probe was moved gradually area, relatively close to the skull base and side (Fig. to posterior parts of the skull echo complexes were cm 2).