Diamond Juan

M. Taveras,

Past,

was one of the last branches of surgery to develop. The first successful removal of a brain tumor was reported by William MacEuen in 1879, who excised a meningioma and also removed some subdural hematomas. In 1884, both Durante in Rome and Godlee in London reported successful removal of intracranial tumors. In 1887, Victor Horsley in London removed a spinal canal tumor localized clinically by his colleague, William Cowers. Around the same period of time, Sir William Cowers stated, “The nervous system is almost enticely inaccessible to direct observation. The exceptions to this are trifling: the termination of one nerve, the optic, can be seen; some of the nerve trunks in the limbs can be felt, either in their normal state or when enlarged by disease. As a rule, the state of the nervous system can be ascertained only by the manner in which its work is done, and morbid states reveal their presence by the derangement of function which they cause.” In 1893, Starr reported 84 operations for brain tumor (1). In 32, the tumor was not found, and the patient died. Similar experiences were reported by others. The announcement of the discovery of x rays by Roentgen on December 28, 1895, was received with considerable enthusiasm by everyone, but it was particularly meaningful to neurologists and surgeons, who saw the obvious need for a means of loEUROSURGERY

Index tory Radiology

term:

Radiology

1990;

Lecture

MD

Neuroradiology:

N

Jubilee

and

radiologists,

his-

175:593-602

1 From the Department of Radiology, Massachusetts General Hospital, 32 Fruit St. Boston, MA 02114. From the 1989 RSNA annual meeting. Received January 19, 1990; accepted January 23. Address reprint requests to the author. RSNA, 1990

Present,

Future’

calizing the lesions of the central nervous system better than clinical evaluation alone. Harvey Cushing, the father of neurologic surgery, reported a case of a gunshot wound in the neck that he had evaluated with x rays in November 1896 (2). One of the earliest published cases of brain tumor diagnosed with x rays was a cerebellar tumor that was in all likelihood well calcified so that it could be seen by this means, even with the rather poor technique available at the time (1899) (3). X rays were used extensively by the U.S. Army during the war with Spain in 1898, and this experience resulted in the publication of a book (4). Many of the patients had problems involving trauma to the skull and bullet wounds. In the United States, an early worker in this field was George E. Pfahler (1874-1957) (5) from Philadelphia, who reported successful diagnosis of some brain tumors. However, the most important contributor to skull radiography was Arthur Sch#{252}ller, from Vienna (1874-1957) (6). He wrote two books on skull radiography, in 1905 and in 1912. The latter was translated into English by F. F. Stocking in 1918 (7). Even though Sch#{252}ller was not a surgeon, he described three operations, including transphenoidal hypophysectomy and anterolateral cordotomy. His name is associated with HandSch#{252}ller-Christian disease, and he also described osteoporosis circumscripta, the early stage of Paget disease in the skull. It is interesting, however, that Sch#{252}ller did not embrace the new techniques of cerebral pneumography and angiography. He left Vienna in 1938 for political reasons and emigrated to Australia at the age of 64. He died 19 years later, in 1957. Abbreviations: communications

ASNR systems.

=

American

Society

DEVELOPMENTAL PERIOD, PART 1 (1918-1939) This period represents the beginning of neuroradiology and started with the introduction of methods that employ contrast material-cerebral pneumoencephalography, myelography, and angiography. Pneumoencephalography Ventriculography

and

In 1913, in the American Journal of Roentgenology (8), Stewart described and provided illustrations of a patient who, after fracture of the posterior wall of the right frontal sinus, developed extensive filling of the ventricular system of the brain with air. The case was also reported by Luckett in Surgery, Gynecology and Obstetrics in 1913 (9). However, the development of ventriculography in 1918 and pneumoencephalography in 1919 by Walter E. Dandy, a neurosurgeon at Johns Hopkins, was done without knowledge of either case report. Rather, Dandy stated, “It is largely due to frequent comment by Dr Haisted on the remarkable power of the intestinal gases to ‘perforate bone’ that my attention was drawn to its practical possibilities in the brain” (10,11). Dandy was working with hydrocephalic children, and thus it was easy to carry out the puncture and the injection of air in exchange for removed cerebrospinal fluid. In fact, he continued to do ventriculography in hydrocephalic subjects for some months before attempting this examination on an adult. Pneumoencephalography and yentriculography developed rather slowly. Harvey Cushing, the most prominent neurosurgeon at that time, used it very little in 1924 and gradually increased the number of ventriculogra-

of Neuroradiology,

PACS

=

picture

archiving

and

593

phy examinations per year until about 1929, when he began to use it frequently (Cushing performed it in three cases in 1924, in 11 in 1928, in 17 in 1929, and in 53 in 1930) (12). An improved apparatus for skull radiography and pneumoencephalography was devised by Erik Lyshoim of Stockholm; this apparatus came to be known as the Lyshoim skull table (manufactured by Schonander) (13). A number of important contributions and a book were published in the United States by Leo Davidoff, who was a neurosurgeon, and Cornelius Dyke, who was a full-time neuroradiologist at the Neurological Institute of New York at Columbia Presbyterian Medical Center. Their book, The Normal Encephalogram, published in 1937, was a classic (14,15). Although Merrill Sosman at the Peter Bent Brigham Hospital, Harvard Medical School, was a general radiologist, his work with Cushing’s neurosurgical patients gave him significant experience, and he became quite knowledgeable in the area, claiming a high degree of accuracy (16,17). He may have influenced Cornelius Dyke, one of his trainees in radiology, to become the first full-time neuroradiologist in the United States as Dyke went to New York to work at the Neurological Institute. The other general radiologist in the 1920s who became quite competent in radiology of the nervous system was John Camp, who worked at the Mayo Clinic (18). Myelography Myelography was first described by Sicard in Paris (19,20). Initially he used iodized oil to treat sciatica and other neurologic conditions. However, perhaps an inadvertent injection of the contrast medium into the subarachnoid space led to the observation that it dropped to the bottom of the spinal canal, and he then got the idea of utilizing it to diagnose obstructions to the normal flow of spinal fluid. Sicard was, in fact, the first investigator to introduce the use of positive contrast media for diagnosis of conditions of the central nervous system. It may well be that he influenced Egas-Moniz, who was a friend of his in Paris. According to Bull (21), air myelography was introduced by H. G. Jacobaeus of Stockholm, who published an article in 1921 (22). After the original description of surgical repair of herniated intervertebral disks by Mixter and Barr in 594.

Radiology

1934, the first article published in a radiology journal dealing with myelographic diagnosis was by Hampton and Robinson (23); all of these authors were from Massachusetts General Hospital. The quality of the images in the latter article is outstanding. Iodized oil was used to perform myelography for a little over 20 years until the introduction of iophendylate in 1944. Cerebral

Angiography

Cerebral angiography required considerably more development and experimentation than did ventriculography and pneumoencephalography. It was originally described by Antonio Caetano de Abreu Freire Egas-Moniz, an extraordinary man. Born and raised in Portugal, he had his medical education in Coimbra, a famous Portuguese university north of Lisbon. His neurology training was in Bordeaux and later in Paris, where at the time there were men like Babinski, Marie, and Dejerine. During the First World War, EgasMoniz was appointed ambassador to Spain, and later foreign minister, and as such, he headed the Portuguese delegation to Versailles to sign the peace treaty with Germany (1919). To determine the most suitable contrast medium for visualization of the arterial system of the brain, EgasMoniz began doing experiments with cadavers and skulls. He tried rubidium, lithium, strontium, ammoniurn, potassium, and sodium iodide at concentrations of 100%, 50%, 20%, and 10%. He also did the same with solutions of lithium, strontium, ammonium, sodium, and potassium bromide. After performing a fair amount of experimental work in dogs and cats, he started using a 70% solution of strontium bromide in humans. In the first three patients Egas-Moniz performed percutaneous puncture of the carotid artery. After three failures, he called in a neurosurgeon, Almeida Lima, to do a cutdown operation and to puncture the carotid artery under direct observation. However, he did not succeed in his next two or three cases, and he switched to 25% sodium iodide, which he knew was well tolerated intravenously. He finally succeeded in his ninth case (24). This story is extremely well recounted by James Bull in his article, “The History of Neuroradiology” (21). Egas-Moniz received the Nobel Prize in physiology and medicine in 1949 for his discovery of the thera-

peutic value of leukotomy in certain psychoses and not for his development of cerebral angiography, although the latter may have been taken into account. Egas-Moniz wrote two books on cerebral angiography, in 1931 (25) and in 1934 (26). It is surprising how much detailed information about cerebral angiography can be found in these early books. Despite Egas-Moniz’s publications in books (which were in French) and in journals outside of Portugal (including the United States), cerebral angiography developed very slowly outside of Portugal. For instance, as late as 1941, Dyke wrote, “Its main indication, in my opinion, is to determine whether or not an aneurysm or an arteriovenous angioma exists; in other words, to differentiate a mass formed by enlargement of one of several blood vessels from a true tumor” (27). Egas-Moniz was able to perform Serial angiography earlier than anyone else because of the development made by one of his radiologic colleagues, J. P. Caldas. Caldas devised an apparatus called a radiocarousel, which permitted the taking of one radiograph per second for 6 seconds. Egas-Moniz was thus able to make some physiologic observations on the circulation of the brain (28). When Egas-Moniz was investigating contrast media, he was not aware of an article that had been published in the United States by Barney Brooks, a surgeon from Washington University Medical Center in St Louis. Brooks described the injection of 100% sodium iodide into the femoral arteries to detect arterial occlusion or lack of occlusion in problem cases. He performed the examination with the patient under nitrous oxide general anesthesia. His report was preceded by an article on experimental work in animals carried out in 1923 (29). DEVELOPMENTAL PART

PERIOD,

2 (1939-1972)

The year 1939 marks an important event that influenced the development of neuroradiology: the First Special International Conference on Cranial Radiology, organized by otolaryngologists Thiempont from Antwerp and Chauss#{233}from Paris. The conference took place in Antwerp, Belgium, in July 1939. While it was not then called Symposium Neuroradiologicum, it nevertheless was considered as the first of these. After an

June

1990

interruption caused by World War II, the second conference (Symposium Neuroradiologicum) was held in Amsterdam in 1949. In the United States, Harold Peterson of the University of Minnesota organized the first postgraduate course in neurologic radiology in November 1939. It is of interest that only about 20% of the program of the international conference in Antwerp was dedicated to the brain, whereas 100% of the postgraduate course at Minnesota was devoted to neurologic radiology. The influence of the symposia on the development of neuroradiology was great because they stimulated interest in the nervous system among established workers and young radiologists. A list of symposia is given in the Table. The 14th symposium will take place in London in June 1990 under the presidency of George DuBoulay. The period from 1939 to 1973 represents the most important period of development for neuroradiology because of improvements in existing techniques and development of new ones. Improvements Techniques

in Existing

Cerebral pneumography.-This technique achieved a pinnacle with the introduction of the fractionated technique of pneumoencephalography in the late 1940s and early 1950s by Eric Lindgren and colleagues in Sweden (30). Other technical improvements, such as autotomography, were introduced (31). Perhaps the final important development in pneumoencephalography was the introduction, in 1963-1964, of a special somersaulting apparatus by Kurt Amplatz (32) and Potts and myself (33) that permitted complete management of the air within the cranial cavity by rotating the patient up to 360#{176} to facilitate Volume

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filling of the part of the ventricular system being examined. Ten years later, pneumoencephalography was eliminated as a diagnostic procedure following the advent of computed tomography (CT). Myelography.-Myelography underwent an important advance with the introduction, in 1944, of the clinical applications of a new contrast medium (iophendylate) by Ramsey, French, and Strain. lophendylate became the most widely used contrast agent for myelography throughout the world (34,35). In some countries, such as Sweden, air continued to be used instead of positive contrast material for a number of years. Harold Peterson was one of the first to perform and recommend the removal of the contrast agent, first iodized oil and later iophendylate (36). Of course, it was much easier to remove the iophendylate because it was not nearly as viscous as iodized oil. The removal of the contrast material became standard practice in the United States and most other countries. Further developments occurred later, with the introduction of watersoluble contrast media for myelography. The earliest water-soluble contrast agent, abrodil, was very irritating to the meninges and the nerve roots and required spinal anesthesia (37). In the late 1960s the organic iodine compound iothalamate (same as Conray [Mallinckrodt, St Louis] for cerebral angiography) was being employed for lumbar myelography only, and later a dimer (two bound molecules of the iothalamate compound) was used extensively in Europe and South America but not in the United States (38,39). These compounds were less irritating than abrodil and did not require general anesthesia, but some patients developed severe muscle spasms in the trunk and lower extremities (40). Metrizamide was finally developed and marketed in the middle 1970s (41,42). Cerebral angiography. -Cerebral angiography progressed and expanded greatly during this period. The slow development of cerebral angiography in the 2 decades following EgasMoniz’s descriptions was undoubtedly related to three problems. The first one was that it required a cutdown procedure despite the fact that routine percutaneous puncture was described in the late 1930s by Loman and Myerson of Boston in 1936 (43) and by Shimidzu of Tokyo in 1937 (44). Perhaps the greatest single advance in cerebral angiography was

the introduction, by Seldinger, of the catheter to replace the needle (45). Interestingly enough, the Seldinger method was not used routinely for cerebral angiography until a full decade later. Amundsen of Oslo deserves credit for introducing this technical advance (46), as well as Kurt Amplatz of the University of Minnesota (47). The second problem was that the radiographic technique and the absence of serial apparatus made the examination somewhat limited. The early development by Caldas, mentioned previously, was not adopted by others, but in the 1940s and early 1950s, serial apparatuses were manufactured and marketed. Among these are the Sanchez-Perez serialograph, capable of up to eight exposures (approximately one per second); the Fairchild camera, an adaptation of an aerial survey camera used during World War II, capable of four exposures per second; and the Schonander film changer, capable of six exposures per second. These units were used sparingly for cerebral angiography in the early periods. Wood and Taveras were the first ones to perform routine serial cerebral angiography since 1952. In 1956, Greitz published his classic work on the study of cerebral circulation with cerebral angiography and established the physiologic norms for the arterial, capillary, and venous phases (48). The third reason why cerebral angiography did not progress as rapidly as it should have in the 1930s and 1940s was the lack of good contrast media. Thorotrast was used and recommended by Egas-Moniz and by Lima, but this was a colloidal suspension that was permanently stored in the reticuloendothelial system of the body, and thorium is slightly radioactive. Diodrast (Winthrop, New York) (and its equivalent in Europe), a 35% solution of an organic iodide compound, was not satisfactory because it was somewhat irritating to the blood vessels of the brain, sometimes leading to convulsions, and it was not very opaque (49,50). Solutions of higher concentration would have been more opaque, but they would have provoked more frequent convulsions and would have caused severe pain when injected into the external carotid branches. In the 1950s Urokon (Mallinckrodt) was introduced, but although it was significantly more opaque than Diodrast, it was still far from being an ideal contrast medium. Diatrizoate (Hypaque; Winthrop-Breon, Radiology

595

#{149}

New York) was a much better contrast medium, and in the late 1950s it virtually replaced all other contrast media for cerebral angiography in the United States. Two technical advances in cerebral angiography are worth mentioning: magnification angiography and subtraction. The former became possible because of industrial production of xray tubes with submillimeter focal spot size but with sufficient output to allow serial angiography. The magnification technique represented a significant improvement in angiography. Subtraction was introduced in 1961 by Ziedses des Plantes at the Symposium Neuroradiologicum in Rome (51). We still use subtraction routinely in angiography of the brain and the spinal cord, and this technique has been further developed by the introduction of digital subtraction angiography, in which the subtraction process is done automatically via a computer. New

Techniques

Ultrasound.-As early as 1947, Dussik et al of Vienna suggested the possibility of using ultrasound (US) to examine the brain (52). The first suggested use of US may well have applied to the brain. However, it was not until 1956 when a Swedish neurosurgeon, Leksell, published an article (and later a monograph) on the use of US to examine the brain after trauma (53). He termed this procedure “echoencephalography.” The absorption of the ultrasound beam and reflected beam by the skull in the adult represented a significant impediment to further development of B-mode US for examination of the brain, but echoencephalography continued to be used for the following 2 decades until other more important procedures, such as CT, came into general use. Brinker and I can be credited with producing some of the early crosssectional images of the brain, which were of fairly low spatial resolution because of the equipment then available. The first portable pivotal-arm US scanner was specially manufactured by the Physionics Laboratory of Denver (54). During the 1960s, much improvement in equipment took place, and this pattern continued in accelerated fashion into the 1970s. The latest development, which started about 10 years ago, is the conversion of analog images into digital images. Some of the newer scanners are entirely digital, and this technol596

#{149} Radiology

ogy has improved spatial resolution of the sonic images. Radionuclide encephalography.-Despite the fact that radioactive iodine was being used to evaluate the function of the thyroid gland in the early 1940s, I credit George Moore, a genera! surgeon at the University of Minnesota, with demonstrating the feasibility of expanding the uses of radioactive isotopes for diagnosis. In 1948, he published a report in Science dealing with the diagnosis of brain tumors by a radioactive isotopic method (55). Moore had been using fluorescein and an ultraviolet lamp to detect abdominal metastases for some time, and he got the idea to Iabel the molecule with radioactive iodine and to use an external probe to detect the radioactivity in the brain. He was extremely enthusiastic about this new technique and claimed over 90% detection accuracy with use of an external counting method. I presume that the high percentage of correct detections that he reported was probably owing to the relatively small group of brain tumors that he examined and, possibly, their large size. However, he stimulated a lot of interest that led to further developments and contributed to the creation of the new specialty of nuclear medicine. An early publication in the new field by Brownell and Sweet at the Massachusetts General Hospital dealt with the use of positron emitters to diagnose brain tumors (56). Radionuclide encephalography became an important noninvasive diagnostic approach for pathologic conditions of the brain. Its use lasted until 1973, when CT was introduced. Although the clinical use of radionuclide encephalography declined, the technique led to other developments such as measurement of cerebral blood flow with krypton-87 and xenon-133 and, later, positron emission tomography, which is now receiving increasing attention. Radionuclides were first used more extensively for diagnosis of neurologic conditions than for diagnosis of lesions of any other organ except the thyroid gland. Diskography.-Diskography was introduced by Lindblom in Stockholm (57). It never became very popular but has been variously used until the present. In this country, Harold Peterson performed about 300 diskography procedures after Lindblom’s visit to Minneapolis but gave it up after deciding that it was not useful compared with myelography. Others were somewhat more enthusiastic about diskography, but in some cen-

ters it was never used extensively. I never accepted diskography as a good diagnostic procedure (58). In the past several years, diskography has become a necessary procedure preceding the treatment of herniated intervertebral disks with the enzyme chymopapain, but again its routine use has been discontinued because the contrast media may interfere with the enzymatic effects. Lindblom tried to perform percutaneous aspiration of intervertebral disks in the early 1950s but did not succeed. More recently in the United States, Gary Onik has succeeded in developing a sufficiently strong suction apparatus that will aspirate disk material through a thin trochar inserted percutaneously, and the method is now undergoing clinical trials in the United States and elsewhere (59). Interventional neuroradiology.-The entire concept was started by a neurosurgeon, Alfred Luessenhop from Georgetown University Hospital in Washington, DC; in 1960, he performed an embolization procedure to treat an arteriovenous malformation of the brain (60). Luessenhop also performed experimental work to determine whether intraarterial manipulations of cerebral vessels would lead to spasm or thrombosis (61,62). Aside from the publications by Luessenhop relatively few publications on interventional neuroradiology appeared in the literature until early 1970. The approach was chiefly restricted to use during intracranial surgery, which meant that it was done either by neurosurgeons or in the operating room with a neuroradiologist assisting the neurosurgeon (63-66). Two case reports that appeared in 1968 (Newton and Adams; Doppman, Di Chiro, and Omaya) dealing with percutaneous embolization of a spinal cord angioma opened new avenues for the treatment of arteriovenous malformations. Although the case report by Newton and Adams appeared in Radiology in 1968, the case was presented informally at the VIII Symposium Neuroradiologicum in Paris in September 1967 (67,68). At the IX Symposium Neuroradiologicum in Gothenberg, Sweden in 1970, three presentations indicated increasing interest in the interventional field on the part of the neuroradiologists. The presentations dealt with magnetically guided catheters, embolization of vascular malformations, and the development of a balloon catheter technique for the treatJune

1990

ment of intracranial aneurysms (6971). At the same symposium, Hilal discussed what this branch of neuroradiology should be called. The terms “remedial radiology” and “interventional radiology” were mentioned. Starting in the early 1970s, a steadily increasing number of publications began to appear dealing with embolization procedures, techniques, equipment, and materials. Two deserve special mention (72,73). However, the credit belongs to Serbinenko, a neurosurgeon from Moscow, for really opening up what we call modern interventional neuroradiology. Training

in Neuroradiology

Two other aspects of the development of neuroradiology during this period deserve special mention. The first is the establishment of special training in neuroradiology. In Europe before 1960 it was possible to obtain fellowships for training in neuroradiology in Sweden (under Lindgren at Serafimer Hospital and Wickbom in Gothenburg), England (under Bull at the National Hospital for Nervous Diseases in London), and France (under Fischgold at La Pitie in Paris). In the United States there was no organized training until 1959-1960, when the National Institute of Neurological Diseases and Blindness established special fellowships for 2-year training programs in neuroradiology for individuals who had completed a full general radiology program. The first two programs established were at the Neurological Institute of Columbia-Presbyterian Medical Center in New York (under me) and the Albert Einstein Medical Center, also in New York (under Mannie M. Schechter) (74). Soon, other programs were established at the University of Minnesota; New York University; Washington University’s Mallinckrodt Institute (St Louis); New York Hospital, Cornell; University of Pittsburgh; University of California, Los Angeles; University of California, San Francisco; Massachusetts General Hospital; Yale Medical Center; Johns Hopkins; University of Miami; and possibly others. When the program ended around 1977, over 200 trainees had been supported for 2 years of training. Thus, in the United States, the National Institutes of Health can be credited with the development of neuroradiology through support of this fellowship training program. Without this support, the young candidates could Volume

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not have afforded 2 additional years of training, and at that time the hospitals would not have agreed to more support beyond residency. By the middle 1970s, institutions and professional groups began to provide the needed support, and thus the training programs continued in greatly expanded fashion to the present. Organizations

in Neuroradiology

The other event of special note was the formation of the American Society of Neuroradiology (ASNR), which I initiated as president of the VII Symposium Neuroradiologicum, to be taking place in New York in 1964. The Society began in 1962 with 14 founding members. The ASNR has grown greatly and has been a source of stimulus for the young radiologists who enter the field of neuroradiology. It has grown, in 27 years, to a membership of about 1,300. The European Society of Neuroradiology was founded in Colmar, France, in September 1969, during a colloquium that was organized by J. P. Braun with the assistance of Wackenheim, Fischgold, Gros, Philipides, Rhomer, Wellauer, and Woringer. A number of local societies in various countries have now been established. Probably the largest of these outside the United States is the Japanese Society of Neuroradiology. In Japan the society’s membership is composed mostly of neurosurgeons, but this may change in the future as more neuroradiologists are trained in Japan. MODERN

PERIOD,

1973-1989

The second developmental period ended with the discovery of CT. A truly dramatic announcement was made by Hounsfield and Ambrose at the meeting of the British Institute of Radiology in April 1972 (75,76). Few Americans attended this meeting, but Dr James Bull brought the inventor, Godfrey Hounsfield, to New York to present his work at a postgraduate course organized by Schechter at the Albert Einstein Medical Center in May 1972. Some of us in neuroradiology were on the faculty of that course and were most impressed with the presentation. I personally got Hounsfield to spend a day or two at the Massachusetts General Hospital, and we immediately started working on research in CT. The following year the first two instruments, pro-

duced by the EMI Company of England, were delivered in the United States, the first to the Mayo Clinic and the second, almost at the same time, to the Massachusetts General Hospital. Afterward, the new technology evolved rapidly. A number of corporations entered the field and some new corporations were formed to exploit the new technology. Possibly the first successful of these was the Ohio Nuclear Corporation, later called Technicare. But even some drug companies, not previously involved in the manufacture of imaging equipment, entered the field. These include G.D. Searle Corporation, Syntex Laboratories, Pfizer Laboratories, and later, Johnson & Johnson through the acquisition of the Technicare Corporation. None of these remained in the CT business for long. The entire business eventually reverted to the usual manufacturers of x-ray imaging products. One of the reasons why CT was such an important development is that it signaled the marriage of the computer to the x-ray beam, and later to other approaches, for generation of images. Magnetic

Resonance

Since its inception over 40 years ago, nuclear magnetic resonance (NMR) spectroscopy has been used as a powerful analytical tool by chemists and physicists. It was originally described in the 1940s by Bloch (from Stanford) and Purcell (from Harvard University), who worked independently (77,78). In spectroscopy all measurements were averaged over the entire sample. Credit is due Paul Lauterbur from Stony Brook, New York, for publishing the first spatially differentiated NMR measurements or NMR images (79). Damadian had published a report dealing with tumor diagnosis but not utilizing NMR imaging (80). Shortly after the publication of Lauterbur’s article, a number of scientists, particularly in England, began investigating this approach. The article by Waldo Hinshaw, an American working in England, and coauthors from Nottingham University demonstrated striking resolution in an image of the human wrist; these images attracted a lot of attention and demonstrated the potential of this new approach for producing high-resolution images (81). I became interested in the possibilities of magnetic resonance (MR) at that time, and the same publication must have Radiology

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influenced others in the United States. We were able to recruit Waldo Hinshaw to join us at the Massachusetts General Hospital in 1978, and a laboratory was soon developed there with the assistance of Technicare Corporation, which had just been acquired by Johnson & Johnson. Other laboratories were established elsewhere in the United States, such as at the University of California, San Francisco, and at Vanderbilt University. Companies were also busy investigating the potential of MR imaging, including General Electric, Siemens, Picker, and Philips. The more advanced imaging work at that time, however, was being carried out in England (81,82), and the earliest MR imaging unit utilizing a superconducting magnet applied to clinical imaging was manufactured by Picker X-Ray Corporation and was installed at the Hammersmith Hospital in London in 1981. It yielded excellent images (83). However, the earliest images of the head were produced by the Thorn-EMI group, with which Hounsfield was associated, starting in 1978 (84). The Nottingham group was an early contributor (they used a resistive magnet), and so was the Aberdeen group (they used very low power magnets, eg, 200-400 C) (8590). The company Oxford Instruments of England deserves credit for producing the great majority of the early human-size superconducting type magnets, which could go up to 1 T and higher. The resistive magnets could not go above 0.15 T and produced a magnetic field that was less homogeneous than that produced by the superconducting magnets. In the United States, General Electric introduced instruments for imaging with higher magnetic field strength (1.5 T). Although the controversy persists as to whether one needs these high values for imaging as compared with lower values of 0.5-1.0 T, I believe everyone agrees that a field strength of 1.5 T or higher would be required to perform spectroscopy. Interventional Neuroradiology

Radiology

PRESENT

AND

FUTURE

Neuroradiology may now be defined as that branch of radiology that deals with disorders of the nervous system. It includes all those modalities utilized in the diagnosis of these conditions, including plain radiography, CT, MR. noninvasive tests to diagnose carotid artery disease, US, myelography, and angiography. We recently included interventional procedures that fall under the category of interventional neuroradiology. Neuroradiology does not ordinarily include head and neck radiology, but in many institutions the neuroradiology staff may handle this area as well. I take some credit (with Dr E. H. Wood) for providing an early definition of what neuroradiology should be, through the publication of the first edition of Diagnostic Neuroradiology in 1964. (The definition was restated in the second edition in 1976.) The concept of neuroradiology has expanded with the introduction of MR and the development of interventional procedures.

(Surgical)

The basic developments that had taken place in the preceding period represented the foundation of what has now become an important branch of neuroradiology. Credit must go to F. A. Serbinenko, a Russian neurosurgeon working at the Burdenko Institute in Moscow, for introducing the technique of using microballoons to facilitate flow598.

directed advancement of the catheter while allowing the inflated microballoon to be detached in place (91). This development revolutionized the field, stimulated the interest of neuroradiologists and some neurosurgeons, and created a rapidly advancing field based on the desire for improved therapy for certain vascular conditions of the brain and spinal cord. Soon thereafter, others in Europe and the United States adopted these technical advances and introduced modifications of their own (92-96). Among these, Debrun deserves special mention (94). I have selected some references from the numerous publications that appeared in the late 1970s. Undoubtedly there are others not included here. With the exception of the late Ren#{233} Djindjian, the early contributing authors listed here still contribute heavily to the field.

Research I continue to be disappointed with the amount of basic research being carried out by neuroradiologists. Research is extremely important because a specialty of medicine that does not generate new knowledge through research will tend to disappear and be absorbed by other specialties. Few neuroradiologists have organized a research program of

their own and have received support from the research-granting institutions such as the National Institute of Neurological Disorders and Stroke (NINDS). This is partly because there is not enough basic training in our programs in radiology and neuroradiology to prepare the individual for research. However, there is another problem that we often disregard. This problem was described well by Dr Murray Goldstein, who is now the Director of the NINDS. In 1975, he was asking for more monies to support more training programs in neuroradiology. As it turned out, the neuroradiology programs were discontinued a year or two later. Nevertheless, his final comment, made in 1975, may still be pertinent to the question of research: “The critical problem in neuroradiology is one of numbers for the future. As numbers increase, the relative proportion of time available for the teaching and research activities of neuroradiologists would increase.” That is, if there are not enough individuals in neuroradiology-if there are always clinical jobs available and the neuroradiologists are busy with clinical work-there is no time left to do research. Technology The future will bring some changes provoked by recent technical and scientific advances. I expect there will be more changes (progress) in MR imaging and spectroscopy than in any other area. The improvements that we may expect could be listed as follows. 1. The speed of data gathering for obtaining images of all types will increase. This hopefully will be done without significant loss of spatial resolution. 2. Single MR images and cine MR images obtained by using a modified form of the echo-planar or other techniques will be perfected, and the resolution will be much better than it is now. 3. Diffusion imaging techniques will improve and will be utilized clinically to differentiate certain tumors and to determine whether some lesions, such as those of multiple sclerosis, are new or old. Diffusion imaging may be applicable to the early diagnosis of ischemic infarction and to the study of certain neoplasms. 4. MR arteriography will be commonplace and will continue to improve through elimination of arti-

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1990

facts and improvements in spatial resolution. MR venography will also improve. It will be possible to use MR to assess blood flow, that is, to obtain tissue perfusion measurements. Will MR studies replace angiography of the brain? The rapid progress being made indicates that they will replace a certain proportion of diagnostic angiography studies, for instance, those performed to detect carotid artery disease in the neck or intracranial saccular aneurysms. More than likely they will not replace angiography performed before surgery or interventional procedures. B-mode US, Doppler US, and the noninvasive tests used to evaluate the carotid circulation may remain because of their simplicity and lower cost. 5. There will be improvement in and an increase in the clinical applications of MR spectroscopy, especially proton MR spectroscopy. It is usually stated that phosphorus spectroscopy requires higher field strengths than are usually employed in the clinical setting, but improvements are taking place and 1.5 T may turn out to be satisfactory. 6. Spatial resolution will increase because of better techniques for controlling artifacts produced by pulsatile and respiratory motion and better surface coils. 7. Coils that can be introduced into the body (eg, prostate gland, heart, esophagus) are being developed. 8. Three-dimensional techniques will permit volumetric measurement of lesions enhanced with gadolinium before and after therapy. Three-dimensional techniques will be used for brain surface mapping before surgery so that surgeons will know the exact relationship of the lesions to the brain surface. 9. It is possible that the future will see a swing away from superconducting magnets to a recently announced development, superferric magnets. A 4.5-T magnet of this type will have a 5-C line at only 50 cm. A 4.5-T prototype with a 30-cm bore has been constructed and is being studied at Baylor in association with the Houston Area Research Center. Also, almost surely we will have higher temperature superconductors, which will tend to reduce maintenance costs. 10. Organ specific and even disease specific contrast media for MR imaging may be developed. 11. Not much further development in CT is anticipated, aside from the possibility of further speeding up Volume

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the exposure, which now is 1-3 seconds in most units, to possibly 0.10.05 second, such as is possible with the unit currently available from the Imatron Corporation. The future may see some important developments in CT if the possibility of producing monochromatic x-ray beams (such as is possible with the synchrotron light source at Brookhaven’s National Laboratory) to produce cross-sectional CT scans comes to fruition. If so, it would be possible to perform arterial and venous imaging with low doses of iodine because a technique that uses a monochromatic beam of x rays at the optimum keV value for iodine would be five to 10 times more sensitive than ordinary CT scanning. Also, it may be possible to perform multiphoton absorptiometry CT to detect intermediate-z elements such as phosphorus, sulphur, chloride, potassium, and calcium. In the future, twoand three-dimensional reformatting with CT will be done very rapidly and will become nearly routine. 12. All radiography may be converted to digital imaging. I can see conversion of skull and spine radiography to digital imaging, which would allow complete manipulation of the images. I also see continuing development of picture archiving and communications systems (PACS), a technology based on conversion of all images to digital ones. Such conversion would be easier in neuroradiology because the majority of the examinations (CT, MR imaging, the few US studies that we do, and angiography) are already in digital form. Only skull and spine radiography and myelography are not. Myelography could easily be converted to digital form because digital fluoroscopy and spot filming are already a reality. Will this lead to the elimination of xray films? I believe that this may well happen eventually, but it will be a fairly long time before it occurs because it is necessary to create a method that will permit broad distribution of and comfortable access to images and permit comparison of images of different types, such as CT scans and MR images, old with new. This is now easily accomplished by simply putting a radiograph next to another image. Thus, the development of the viewing station is the number one problem in PACS not only because of the need for rapid viewing and rapid recall and transmission but also because of the cost. The initial cost must be brought down to a reasonable level. 13. In the not too distant future,

typed reports will be prepared directly from voice input. It is only a matter of improving the computer equipment and programs that are now being developed. I visualize the neuroradiologist in front of a multiple-screen viewing station without xray films, dictating reports without a secretary or a typical recording unit. I suspect that only a small percentage of the reports, possibly 10%, might require regular dictation. 14. Interventional neuroradiology will grow rapidly and in time will extend to other areas, such as the intervertebral disks. However, the latter aspect will vary between interventional neuroradiologists and between institutions, for it is more than likely that orthopedists and neurosurgeons will be performing percutaneous diskectomies. Training Will training in this field continue as it is now, or will it change? I believe that the 2-year training period following general radiologic training will continue to be the norm in the majority of training programs. The proposal that an individual would be sufficiently trained in neuroradiology in 1 year I consider erroneous. Experience has amply shown that these individuals know more neuroradiology than other radiologists who have not had the same exposure, but they do not have sufficient depth of knowledge and experience to be true consultants. One possibility is implementing programs similar to the program at the Massachusetts General Hospital. This program has already been adopted by some institutions, and I hope it will continue to extend to others. The last year, or equivalent, of the 4-year program is devoted to neuroradiology, and after completion of the 4th year, the individual takes an additional (5th) year of neuroradiology training. In that way, he or she will have 3 years of general radiology and 2 years of neuroradiology. It saves the individual 1 year. How about training in interventional neuroradiology? I believe every neuroradiologist should have some exposure to interventional neuroradiology, but if he or she wishes to concentrate on this area, it would be necessary to have a special program. Instead of 2 years, as indicated above, the training program would consist of 1 year of general neuroradiology, 1 year of interventional neuroradiology, and a 3rd year of neuroRadiology

#{149} 599

surgical training-possibly while continuing involvement in interventional procedures-giving a total of 3 years in general radiology and 3 years in neuroradiology including interventional radiology. The exact program would vary depending on the institution and the circumstances. The

Specialty

of Neuroradiology

Perhaps the most important problem that the neuroradiologist will face in the future is the question of turf relating to interventional procedures. I firmly believe that needs are created by the availability of services and not the other way around. Sometimes new knowledge will call attention to the need, and sometimes the knowledge is there, but if there is no one to provide the services, nothing happens. As soon as the services become available, the need is sharply recognized and demands are made to take care of it. A need has been created in the area that we now call interventional or surgical neuroradiology. Who is demanding these services? The services are in demand by neurosurgeons, who are very interested in helping and solving the problems of the patients who are referred to them for consultation or treatment. Therefore, I believe that if neuroradiologists can provide the services demanded by the neurosurgeons, interventional neuroradiology will remain in neuroradiology. On the other hand, if not enough effort is made to train neuroradiologists, or if no one in neuroradiology is interested in training in interventional procedures, then this branch will be taken over by the neurosurgeons as a matter of necessity. A question being asked today is whether neuroradiology will remain as a whole subspecialty or whether it will split into more subspecialties. The split could be into two parts (for classic and interventional procedures), three parts (classic, MR, and interventional procedures), or even four parts (imaging of the skull and spine, including CT and myelography; MR imaging; angiography [possibly performed by general angiographers]; and interventional procedures). It is my definite opinion that any split would be disastrous for the subspecialty. I would like to quote from some well-known neuroradiologists who I asked to express their thoughts about the present and future of the subspe600

Radiology

#{149}

cialty. Quoting from Professor Hilal at the Columbia-Presbyterian Neurological Institute:

Sadek

I believe that the neuroradiologist may have to become as familiar with the regional metabolic functions of the brain as his familiarity with the regional vascular anatomy. The regional metabolic data will be easily accessible on machines available for regular imaging at an affordable cost. This will lead to a widespread use in an environment where the neuroradiologist may have to protect his turf from the neurologist. I can see an increasing tendency to separate the interventional neuroradiological procedures. It is my position that a total separation will weaken both branches. The rapidly increasing armamentarium of instrumentation and embolization material has made interventional radiology easier and more effective. A larger number of neuroradiologists will be able to carry out a substantial part of neuro interventional procedures. There would always remain some highly specialized procedures that may require referral to the big centers. The turf battle is going to be between the neuroradiologist and the neurosurgeon, and I believe it is the third-party payer that is going to decide on who can do it in a more cost-effective way with least complications. ...

Professor Torgny Greitz from Stockholm, speaking about physiologic investigation, worries that “neuroradiologists need to get more involved and to maintain their involvement in order to learn it well. The only way to keep control of a method is to master this method. One may ask whether it is too late to grasp control of the physiologic aspects of magnetic resonance, ultrasound, and PET.” From Professor Sten Cronqvist of Lund, Sweden: “A specialist is someone who knows most or all about the possibilities of all the different techniques and procedures used in his field-not necessarily mastering all of them personally. To take optimal advantage of this knowledge, the neuroradiologist should be given a problem to solve-not necessarily be asked to perform a specific examination, i.e., we should work and be considered as consultants.” From Professor Hans Newton of .

.

.

the University Francisco:

of California,

San

Although the diagnostic accuracy of neurologic problems has increased dramatically, many of these disease processes cannot be treated. The cost of diagnostic studies are at present so high, that economic recession might have a major impact on diagnostic neuroradiology. This is particularly true since many of the advanced neuroradiologic techniques have not improved patient outcome significantly. The “cost-effectiveness” of the various neuroradiologic techniques will therefore be looked at more closely. With the advent of digital techniques, the nature of neuroradiologic practice has changed dramatically. The advances in MRI as well as future advances in vascular MR imaging will, in my opinion, completely eliminate diagnostic angiography from our field. The recent advance of advanced interventional techniques will result in two types of neuroradiologic practice, namely diagnostic and interventional neuroradiology. In the future, therefore, I believe that diagnostic neuroradiology will be concerned primarily with interpretation of MR, and to a lesser extent, CT scans. Angiographic procedures will be performed primarily in patients requiring interventional techniques. These studies will then be performed by mdividuals particularly adept in these procedures, i.e., the interventional neuroradiologist. .

.

.

.

A most provocative from Professor George from London.

.

.

statement DuBoulay

came

Perhaps an important “groundrule” that controlled the development of our specialty and will continue to influence it, is the relationship between diagnosis and treatment. Neuroradiological diagnosis is not a self-sustaining discipline. [If] or when tumors are zapped by magic bullets (as they may be), degenerative vascular diseases are largely prevented by diet and aspirin (or similar), prenatal genetic analysis avoids developmental and enzyme abnormalities, bacterial infections are even better controlled by antibiotics, and viruses are more easily detectable and at last immobilized, we, in the most healthy naJune

1990

tions, will have nothing but wounds and accidents to treat. As the aging process becomes more fully understood, largely preventable and to a degree reversible, during the first century of the third millennium, the people of the richer nations will have become so wise, and the population so tightly controlled by law and custom, that even accidents and mayhem will be rare. Neuroradiology for humans will wither away. I am not as pessimistic as Hans Newton or George DuBoulay and would like to state that I adhere to the old saying, “The more things change, the more they seem to stay the same.” However, the slow changes that we experience in our lifetime do not occur in the best way if left alone. They require considerable vigilance and effort on the part of those interested in maintaining the existing balances between the medical specialties, medical care in general, individual and institutional providers, and government and the insurance industry. U

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June

1990