-
DIAGNOSTIC ULTRASOUND THE VIEW FROM DOWN UNDER bjr G . Kossoff
This paper was presented at the Dallas meeting of the American Institute of Ultrasound in Medicine, November 1 , 1977.
This year marks the 25th anniversary of cross-sectional echography. I would like on this occasion t o review the progress that has been achieved by diagnostic ultrasound, look a t the various factors that have influenced the acceptance of the different ultrasonic procedures, and try t o predict some of the developments that are likely to occur in the future. The first report in the literature t o discuss the potential applications of echographic examination was published in 1949 by Ludwick and Strutters, who discussed the use of ultrasound to detect gallstones. That year, Wild in Minneapolis and Howry in Denver also commenced their studies on ultrasound. In 1950, Wild was the first investigator to publish an A mode echogram of diseased tissue, a strip of human stomach tissue containing a malignant ulcer. That same year Wild showed that echoes could be obtained from cerebral tumors. It quickly became apparent that an interdisciplinary approach was necessary to achieve advances in the field. Thus Wild joined forces with Reid, while I-lowry obtained engineering assistance from Bliss. In 1952, 25 years ago, these investigators published the first cross-sectional images of the breast and abdomen respectively. The two other major ultrasonic examination techniques were described shortly after. The M mode technique was developed by Edler and Hertz in 1954 and the Doppler technique by Satamura and Nimura in 1955. That year Howry and Holmes elaborated on cross-sectional echography and formulated the principle of compound scanning. They illustrated the application of the method by some superb images of the neck. The enunciation of the fundamental principles of echography was completed in 1958, when Donald and Brown described contact scanning and applied this method of couplFrom lhv Ultrasonics Institute. S v d n e v . Australia. For reprints c o n t a c t : G . Kossoff. Ultrasonics 5 Hirkson Road. Sydnev 2000 Australia. 144
Institule.
ing t o obstetrical and gynecological examinations. A common feature of all of these developments is that they were initiated by a physician interested in advancing the clinical state of art of his specialty and an engineer consultant on the technical aspects of the project. The Ultrasonic Research Section of the Commonwealth Acoustic Laboratories of Australia, now the Ultrasonics Institute, was created in 1959. The brief of the Institute is to undertake research into phenomena that occur during the propagation of ultrasound in tissue. For this reasonnot because we live down u n d e r a t our Institute the roles of the physician and the engineer are reversed: physicians act as consultants to engineers on the clinical applications of the projects. Most new medical applications take about 1 0 years t o reach clinical acceptance. It is not surprising that the main developments in the 1960s were concerned with technological advances. In 1963 Physionics introduced the first commercial contact scanner. The next major development occurred in 1966, when Siemens Equipment released its first real time scanner. A number of major technological advances followed in quick succession: Fry introduced computers into echography in 1967, Somer published the first paper on phased array systems in 1968, Peranneau developed the pulsed Doppler system in 1969, and our Institute introduced the concept of gray scale echography in 1971. Several major clinical developments occurred during the 1960s. Probably the most important of these were Donald's introduction in 1961 of the use of the biparietal diameter to determine the gestational age of the fetus and the visualization of the placenta by the Denver group in 1965. These two developments played a major role in the clinical acceptance of diagnostic ultrasound in obstetrics. The M mode JCU. Vol. 6. 1 4 3 - 2 1 4 (1978).3 1 9 7 8 . J o h n Inc.. 0091 275117810006-0144 $01.00.
%ilt,v
arid S o n s .
technique was introduced in the USA in 1962 by Joyner and Reid. For the first few years the technique was restricted to the examination of the mitral valve. Major advances were achieved when it was shown that the method could also examine the left ventricle. With this development, cardiology was the second specialty to accept diagnostic ultrasound in its range of diagnostic procedures. The clinical acceptance of diagnostic ultrasound in an ever-increasing variety of applications is characterizing the seventies. Despite the fact that the number of centers providing ultrasonic diagnostic services is doubling every two years, most centers report that the number of patients that they examine also doubles every two years. Many centers have now more than one scanner, and it is estimated that more than half of next year’s sales will go to departments that already have one instrument. The estimated market in the USA alone exceeds $100 million, and most market surveys project that the field will grow at an annual rate exceeding 15%well into the eighties. An interesting phenomenon has arisen in the last several years. As a new technique or procedure develops, it attracts a considerable amount of attention at the clinical research level and a large percentage of papers presented at meetings are devoted to a detailed analysis of the technique. Then, as the major issues raised by the method are resolved, the technique is relegated to routine clinical use and attention focuses on the next development. Thus in 1973-74, considerable attention was given to the application of ultrasound to the visualization of the liver and the kidneys. These two years are sometimes referred t o as “the golden years of the abdomen.’’ By 1975, most manufacturers had released gray scale equipment and the attention of investigators had turned t o gray scale echography. To me, 1975 was the year of gray scale. One of the major applications of gray scale is the visualization of the vasculature of the upper abdomen-this information can be used to localize the pancreas. Thus by 1976, most investigators had shifted to the examination of the pancreas. Indeed, some people have used the ability to visualize the pancreas as a measure of equipment performance. Nineteen seventy-six was the year of the pancreas. A major advance in real time technology was made in 1973 by the development of the lineararray and the focused phased-array transducers. This development stimulated a number of manuVOLUME 6 . NUMBER 3
facturers t o release a variety of mechanical and electronical real time equipment; 1977, I believe, is the year of real time. The major factor that has influenced the acceptance of ultrasound in obstetrics was its ability to provide accurate dimension information. This has allowed measurement of the size of the fetus; by repeat examinations we can estimate growth rate. It is perhaps a backward step that we express the result of the ultrasonic examination in terms of the fetal gestational age rather than specific dimensions. This estimate involves the correlation factor that exists between the size of the fetus and its gestational age’; while we know that this correlation holds well in early pregnancy, it is less reliable in late pregnancy. A more reliable method which is well understood by obstetricians and which is well-suited to the dimensional measurement capability of ultrasound would be to express the size of the fetus by its weight. This measurement can be performed easily by measuring the area of the fetus on serial echograms, and it can be easily implemented on automated scanners that rapidly acquire a set of such images. Cardiology was the second specialty to accept ultrasound in its range of diagnostic procedures. Ultrasound did not gain widespread acceptance until it could be shown that the technique could be applied t o a range of applications. It behooves those of us whose careers are devoted to the development of new techniques to address ourselves to techniques that are likely to be applied broadly. Gray scale echography has had the shortest transition phase between development and acceptance. The method allows accurate distinction between cystic and solid lesions and the reliable identification of liquid-filled structures as small as 2 mm in diameter. It can also portray abnormal and pathological tissues by their characteristic patterns. However, it is probably the transformation of the schematic sections that used to be obtained with bistable equipment to images that resemble anatomical sections that has played the greatest role in its acceptance. Ultrasonic images can now be interpreted by less well-trained personnel and the referring physician no longer regards the interpretation of ultrasonic images as some form of educated guess work, We must remember that the majority of patients are referred for examination by physicians who have little expertise in ultrasound, and anything that can be done to improve their appreciation of the value of the ultrasonic information will increase the number of patients that are referred for examinations. 145
F I G U R E 1. A breast echogram in patient with multiple cysts in both breasts.
The original gray scale technique developed in our Institute was implemented on mechanized scanners using a photographic film as a display. The technique was also applied in our Institute on manually scanned equipment. This equipment was operated by skilled sonographers and in their hands the technique provided highquality images. Unfortunately the magnitude of an echo displayed on an integrating device such as a photographic film also depends on the speed of scanning and the degree and nature of the. scan. Thus less consistent results are obtained with less well-trained personnel. The major impact of scan converters has been to reduce the dependence of the quality of manually scanned images on the skill of the operator. This development, which produces reliable results in average hands, has played an important role in the acceptance of the gray scale technique. Automation will have a significant role because it will ensure that a constant speed and scanning pattern is undertaken in all procedures and thus provide repeatable images. It is always difficult to predict developments that are likely to occur in the future. I suspect that the concentration of attention will continue over the next few years. On this premise, I believe that the attention of investigators next year will continue to focus on real time. By 1979, however, I believe that the attention of investigators will turn to the examination of the breast. This superficial organ, which was the first organ to be examined 25 yeak ago, has only in the last five years come within the realm of investigation by diagnostic ultrasound. The primary reason for this long latent period has been the highly heterogeneous echo pattern that is obtained from the constituent tissues of the breast. This means that the detection and the diagnosis of pathological changes is much more difficult. Only in the last five years has research with water bath instruments shown that ultrasound has a role in the examination of the breast, particularly in young women where it is desirable t o avoid ionizing radiation exposure. Figure 1 illustrates the type of information that ultrasound can obtain about the constituent tissues of the breast. Ultrasound will not 146
F I G U R E 2. Two transverse sections through the abdomen. The stdmach and the duodenum are filled with methylcellulose.
replace xeroradiography, as current results indicate that the techniques are complementary. Ultrasound works best in the young breast in which the low level of echoes associated with malignant changes is more readily visualized in the complex of stronger echoes obtained from glandular tissue. Xeroradiography , on the other hand, works best in the older breast where the large amount of fat infiltration makes the changes associated with malignancy more difficult t o determine by ultrasound. If ultrasound can identify high-risk patients, they could then be examined regularly by ultrasound or other methods such as thermography and xeroradiography. Potentially, ultrasound may also be developed to show premalignant changes in the breast, which would open up a new vast area of application. By 1980, the examination of the stomach will become of major interest. Work at the Royal Hospital for Women, Sydney has demonstrated that, much like using the full bladder t o lift the uterus above the symphysis pubis, filling the stomach and the duodenum with an inert J O U R N A L O F CLINICAL U L T R A S O U N D
F I G U R E 3. Two horizontal sections of brain of a 2 weeks old infant with moderate hydrocephaly,
liquid may be used t o push the bowel out of the way t o create an acoustic window. This allows the examination of organs such as the pancreas, which are often shadowed by these air-filled structures. An ingested methyl cellulose suspension produces small echoes that allow demonstration of the outlines of the stomach wall, particularly the anterior wall which is difficult to visualize by radiography. Figure 2 shows two transverse sections through the abdomen of a patient. The figure illustrates the type of detail that can be obtained from the stomach, the duodenum, and posterior structures. The examination of the stomach is more easily performed on a prone patient, as any remaining air in the stomach floats into the fundus or abuts the posterior wall. In the supine position, the remaining air floats against the anterior wall and shadows all posterior information. By 1980, pediatric echography will also be more extensively used. In some applications the examination will use the experience developed in adults with the extra requirements necessary for the visualization of similar but smaller structures in .the infant. Other applications, such as examination of the brain, will be unique to pediatrics. The less ossified skull of infants does not impede t o the same extent the passage of ultrasound and this allows the visualization of detail which rivals that obtained by computerized tomography without the necessity of exposing the infant to ionizing radiation or anesthesia. Figure 3 is an example of two head echograms showing enlarged lateral and third ventricles in a young infant with moderate hydrocephaly. Similarly in infants, the bony sternum and the ribs do not impede t o the same extent the passage of ultrasound and the cross-sectional examination the breast and mediastinum will provide unique diagnostic information. In the early eighties, our interest will also center on the measurement of blood flow in deep vessels. Preliminary results on the marriage of VOLUME 6 . NUMBER 3
Average velocity
C jD
=
-
2f*COS0
F I G U R E 4. Combined B mode and pulsed doppler method for quantitative measurement of blood flow in umbilical vein of fetus.
B mode echography with pulsed Doppler has shown that, by combining these two methods, one can identify and measure the diameter of vessels, select the optimum line of sight, and by picking only the Doppler frequency shift signal originating from the selected area, measure quantitatively the blood flow in that vessel. We have performed quantitative measurements of blood flow in the fetal umbilical vein and in the right branch of the portal vein. The application of the method is illustrated in Figure 4 and some of the measured values are shown in Table I. Note that the umbilical blood flow in fetus of various gestational ages appears constant at 105 ml/min/kg fetal weight. It is probably unwise to speculate on developments that are likely t o occur in the later eighties. I suspect that tissue characterization studies will have come into their own and that the increased range of application studies will have opened new frontiers in ultrasonic examination. For instance, tissue characterization of fetal lung development would open up a new and broad field of application in obstetrics that would allow us t o dispense with amniocentesis and the lecithin sphingomyelin ratio test to estimate fetal maturity. 147
TABLE I Gestational Age weeks
25% 28 30 % 30% 35 36 36 36% 37 37 Y 2 38 % 40
Weight of Fetus Kg
Diameter of Vein mm
Average Velocity cm sec-1
Flow in Vein mi min-1
ml min-lkg-1
0.88 1.I 1.4 1.4 2.4 2.6 2.6 2.7 2.8 2.9 3 .O 3.2
5.0 6.5 6.3 6.0 7.5 7.5 7.3 6.6 9.0 8.2 6.6 8.5
8.4 6.3 6.7 9.7 11.2 9.4 8.3 17 6.1 8.0 16.0 9.8
99 125 125 165 297 249 208 349 233 253 328 334
112 114 90 118 126 96 80 129 83 87 109 104
No discussion of the future role of diagnostic ultrasound would be complete without some mention of the impact that computerized tomography (CT) has made on organ imaging. Before the advent of CT and to a lesser extent of gray scale echography, a relatively clear distinction existed between the roles of radiology, nuclear medicine, and ultrasound. Radiology was used primarily to examine highcontrast structures. It produced projected views of the examined organs. Nuclear medicine also provided projected views, but the resolution of the images was relatively poor and the technique was used primarily to determine the functional status of tissue. Ultrasound bridged those two disciplines and provided cross-sectional views of soft-tissue organs. The situation has now changed dramatically. Xray and nuclear CT provides cross-sectional views of soft-tissue organs while gray scale visualizes the texture of tissues seen as hot or cold spots on nuclear scans. Doppler ultrasound provides functional blood flow information. Thus the distinction between anatomy and function has become blurred, and I believe it is more appropriate to refer to the actual parameters of tissues that are measured by the three specialties, namely the xray absorption in radiology, the uptake of radiopharmaceutical agents in nuclear medicine, and the acoustic reflectivity and attentuation of ultrasound. These three basic properties of tissue are independent, and it is unlikely that any one technique will supplement the other. Nevertheless the high cost of the equipment and the enthusiasm that has accompanied the purchase of CT equipment has attracted the attention of administrators who have the respon148
Flow/Weight
sibility for the distribution of medical funds. Recommendations are establishing scientific investigations to determine the role of the various modalities to assure optimum utilization of the finite resources that exist in all countries for the provision of patient care. The political pressures generated by these factors may force the creation of organ imaging centers where the referring physician, in consultation with the organ imaging specialist, will decide which test should be employed t o obtain the necessary diagnostic information at minimum cost to the community. Because the different skills that exist in radiology, nuclear medicine, and ultrasound are likely to become more complex, it is unlikely that there will be a sufficient number of organ imaging specialists who will have sufficient expertise in all three fields. One approach that is being adopted in some hospitals in Australia has been the establishment of organ imaging centers consisting of the departments of radiology, nuclear medicine, and ultrasound. The independent status of the three specialties is respected; but common requirements are pooled to minimize cost. Although diagnostic ultrasound is now an established, rapidly expanding, special branch of medical practice, diagnostic ultrasound is limited because no certificates of professional competence are issued nor is the specialty recognized as such by the medical authorities. Recognizing these limitations and being aware of the types of abuses that could result if these deficiencies were not corrected, the Australian Society for Ultrasound in Medicine and Biology has in the past year initiated action that should help to overcome some of these difficulties. The J O U R N A L O F CLINICAL ULTRASOUND
Australian Society is a body similar t o the AIUM. It is a professional society of investigators interested in advancing the knowledge and application of diagnostic ultrasound. The Society a t present has over 350 members. Approximately 250 of these are medical practitioners, and 60% are radiologists. In September 1976, following a motion passed at its general meeting, the Society looked a t the various areas of applications covered by ultrasound and a t the specialties in Australia that provide training in ultrasound. At a special meeting held three months later, it was unanimously agreed that, due t o the broad area of medical specialties that employ ultrasound and the paucity of training provided by the existing specialties, ultrasound was not directly related t o any one specialty and that the only national body in Australia with expertise in the field was the Australian Society itself. It was then moved that the Society should establish a standard of training required for the practice of diagnostic ultrasound and that this would be best served by establishing the Diploma of Diagnostic Ultrasound which would be open to medical practitioners registered in Australia and New Zealand. The qualifications for the Diploma were to be similar to those which currently apply to other specialties. Exemptions were created for candidates who already hold specialist qualifications in radiology, nuclear medicine, obstetrics and gynecology, surgery, general medicine, cardiology, and ophthalmology. These candidates could apply for examination for the Diploma after two years of experience in ultrasound. A Board of Examiners was set up and invitations for foundation memberships were announced. Eighty-five applications were received for foundation membership. The Board of Examiners of the Society elected that the Foundation Diploma be awarded to 46 applicants. Nineteen applicants were invited to take the examination
V O L U M E 6. N U h l B E R 3
later in the year and another 25 applicants were invited t o take the examination next year. The examinations of the first 19 applicants were held in June 1977 and the Diploma was awarded to 17 candidates. Six of these were cardiologists. Since then, 20 more applications for examinations have been received. By late 1978 it is likely that over 100 Diplomas will have been awarded. If one considers that the population of Australia is a fifteenth that of the USA, similar action by an appropriate body in the USA would award over 1,500 Diplomas t o US medical practitioners with experience in diagnostic ultrasound. The Australian Society has also approached the National Specialist Qualification Advisory Committee of Australia t o recognize diagnostic ultrasound as a medical specialty. The application is under review and a decision on the matter will be made later this year. The Australian Society also has a sonographers' section similar to ASU'l'S, and the question of certification of sonographers is also being considered. As yet this application is not as fully developed, as it was considered that the certification of medical practitioners was by far the more pressing issue. The Australian Society is closely following the action of ASUTS on this subject and will probably adopt many of the requirements recommended by ASUTS . In summary it is clear that over the last 25 years diagnostic ultrasound has developed into a major specialty and that this specialty will continue t o grow. Many of us in Australia consider that as more medical practitioners take up ultrasound on a full time basis, a critical number of people will be reached that will ensure that ultrasound will become recognized as a new medical specialty. We believe that this development, when coordinated and integrated with other specialties, will improve the practice of organ imaging and thus contribute in real terms t o t h e quality of care provided to the patient. 4~
149
DIAGNOSTIC ULTRASOUND THE VIEW FROM DOWN UNDER bjr G . Kossoff
This paper was presented at the Dallas meeting of the American Institute of Ultrasound in Medicine, November 1 , 1977.
This year marks the 25th anniversary of cross-sectional echography. I would like on this occasion t o review the progress that has been achieved by diagnostic ultrasound, look a t the various factors that have influenced the acceptance of the different ultrasonic procedures, and try t o predict some of the developments that are likely to occur in the future. The first report in the literature t o discuss the potential applications of echographic examination was published in 1949 by Ludwick and Strutters, who discussed the use of ultrasound to detect gallstones. That year, Wild in Minneapolis and Howry in Denver also commenced their studies on ultrasound. In 1950, Wild was the first investigator to publish an A mode echogram of diseased tissue, a strip of human stomach tissue containing a malignant ulcer. That same year Wild showed that echoes could be obtained from cerebral tumors. It quickly became apparent that an interdisciplinary approach was necessary to achieve advances in the field. Thus Wild joined forces with Reid, while I-lowry obtained engineering assistance from Bliss. In 1952, 25 years ago, these investigators published the first cross-sectional images of the breast and abdomen respectively. The two other major ultrasonic examination techniques were described shortly after. The M mode technique was developed by Edler and Hertz in 1954 and the Doppler technique by Satamura and Nimura in 1955. That year Howry and Holmes elaborated on cross-sectional echography and formulated the principle of compound scanning. They illustrated the application of the method by some superb images of the neck. The enunciation of the fundamental principles of echography was completed in 1958, when Donald and Brown described contact scanning and applied this method of couplFrom lhv Ultrasonics Institute. S v d n e v . Australia. For reprints c o n t a c t : G . Kossoff. Ultrasonics 5 Hirkson Road. Sydnev 2000 Australia. 144
Institule.
ing t o obstetrical and gynecological examinations. A common feature of all of these developments is that they were initiated by a physician interested in advancing the clinical state of art of his specialty and an engineer consultant on the technical aspects of the project. The Ultrasonic Research Section of the Commonwealth Acoustic Laboratories of Australia, now the Ultrasonics Institute, was created in 1959. The brief of the Institute is to undertake research into phenomena that occur during the propagation of ultrasound in tissue. For this reasonnot because we live down u n d e r a t our Institute the roles of the physician and the engineer are reversed: physicians act as consultants to engineers on the clinical applications of the projects. Most new medical applications take about 1 0 years t o reach clinical acceptance. It is not surprising that the main developments in the 1960s were concerned with technological advances. In 1963 Physionics introduced the first commercial contact scanner. The next major development occurred in 1966, when Siemens Equipment released its first real time scanner. A number of major technological advances followed in quick succession: Fry introduced computers into echography in 1967, Somer published the first paper on phased array systems in 1968, Peranneau developed the pulsed Doppler system in 1969, and our Institute introduced the concept of gray scale echography in 1971. Several major clinical developments occurred during the 1960s. Probably the most important of these were Donald's introduction in 1961 of the use of the biparietal diameter to determine the gestational age of the fetus and the visualization of the placenta by the Denver group in 1965. These two developments played a major role in the clinical acceptance of diagnostic ultrasound in obstetrics. The M mode JCU. Vol. 6. 1 4 3 - 2 1 4 (1978).3 1 9 7 8 . J o h n Inc.. 0091 275117810006-0144 $01.00.
%ilt,v
arid S o n s .
technique was introduced in the USA in 1962 by Joyner and Reid. For the first few years the technique was restricted to the examination of the mitral valve. Major advances were achieved when it was shown that the method could also examine the left ventricle. With this development, cardiology was the second specialty to accept diagnostic ultrasound in its range of diagnostic procedures. The clinical acceptance of diagnostic ultrasound in an ever-increasing variety of applications is characterizing the seventies. Despite the fact that the number of centers providing ultrasonic diagnostic services is doubling every two years, most centers report that the number of patients that they examine also doubles every two years. Many centers have now more than one scanner, and it is estimated that more than half of next year’s sales will go to departments that already have one instrument. The estimated market in the USA alone exceeds $100 million, and most market surveys project that the field will grow at an annual rate exceeding 15%well into the eighties. An interesting phenomenon has arisen in the last several years. As a new technique or procedure develops, it attracts a considerable amount of attention at the clinical research level and a large percentage of papers presented at meetings are devoted to a detailed analysis of the technique. Then, as the major issues raised by the method are resolved, the technique is relegated to routine clinical use and attention focuses on the next development. Thus in 1973-74, considerable attention was given to the application of ultrasound to the visualization of the liver and the kidneys. These two years are sometimes referred t o as “the golden years of the abdomen.’’ By 1975, most manufacturers had released gray scale equipment and the attention of investigators had turned t o gray scale echography. To me, 1975 was the year of gray scale. One of the major applications of gray scale is the visualization of the vasculature of the upper abdomen-this information can be used to localize the pancreas. Thus by 1976, most investigators had shifted to the examination of the pancreas. Indeed, some people have used the ability to visualize the pancreas as a measure of equipment performance. Nineteen seventy-six was the year of the pancreas. A major advance in real time technology was made in 1973 by the development of the lineararray and the focused phased-array transducers. This development stimulated a number of manuVOLUME 6 . NUMBER 3
facturers t o release a variety of mechanical and electronical real time equipment; 1977, I believe, is the year of real time. The major factor that has influenced the acceptance of ultrasound in obstetrics was its ability to provide accurate dimension information. This has allowed measurement of the size of the fetus; by repeat examinations we can estimate growth rate. It is perhaps a backward step that we express the result of the ultrasonic examination in terms of the fetal gestational age rather than specific dimensions. This estimate involves the correlation factor that exists between the size of the fetus and its gestational age’; while we know that this correlation holds well in early pregnancy, it is less reliable in late pregnancy. A more reliable method which is well understood by obstetricians and which is well-suited to the dimensional measurement capability of ultrasound would be to express the size of the fetus by its weight. This measurement can be performed easily by measuring the area of the fetus on serial echograms, and it can be easily implemented on automated scanners that rapidly acquire a set of such images. Cardiology was the second specialty to accept ultrasound in its range of diagnostic procedures. Ultrasound did not gain widespread acceptance until it could be shown that the technique could be applied t o a range of applications. It behooves those of us whose careers are devoted to the development of new techniques to address ourselves to techniques that are likely to be applied broadly. Gray scale echography has had the shortest transition phase between development and acceptance. The method allows accurate distinction between cystic and solid lesions and the reliable identification of liquid-filled structures as small as 2 mm in diameter. It can also portray abnormal and pathological tissues by their characteristic patterns. However, it is probably the transformation of the schematic sections that used to be obtained with bistable equipment to images that resemble anatomical sections that has played the greatest role in its acceptance. Ultrasonic images can now be interpreted by less well-trained personnel and the referring physician no longer regards the interpretation of ultrasonic images as some form of educated guess work, We must remember that the majority of patients are referred for examination by physicians who have little expertise in ultrasound, and anything that can be done to improve their appreciation of the value of the ultrasonic information will increase the number of patients that are referred for examinations. 145
F I G U R E 1. A breast echogram in patient with multiple cysts in both breasts.
The original gray scale technique developed in our Institute was implemented on mechanized scanners using a photographic film as a display. The technique was also applied in our Institute on manually scanned equipment. This equipment was operated by skilled sonographers and in their hands the technique provided highquality images. Unfortunately the magnitude of an echo displayed on an integrating device such as a photographic film also depends on the speed of scanning and the degree and nature of the. scan. Thus less consistent results are obtained with less well-trained personnel. The major impact of scan converters has been to reduce the dependence of the quality of manually scanned images on the skill of the operator. This development, which produces reliable results in average hands, has played an important role in the acceptance of the gray scale technique. Automation will have a significant role because it will ensure that a constant speed and scanning pattern is undertaken in all procedures and thus provide repeatable images. It is always difficult to predict developments that are likely to occur in the future. I suspect that the concentration of attention will continue over the next few years. On this premise, I believe that the attention of investigators next year will continue to focus on real time. By 1979, however, I believe that the attention of investigators will turn to the examination of the breast. This superficial organ, which was the first organ to be examined 25 yeak ago, has only in the last five years come within the realm of investigation by diagnostic ultrasound. The primary reason for this long latent period has been the highly heterogeneous echo pattern that is obtained from the constituent tissues of the breast. This means that the detection and the diagnosis of pathological changes is much more difficult. Only in the last five years has research with water bath instruments shown that ultrasound has a role in the examination of the breast, particularly in young women where it is desirable t o avoid ionizing radiation exposure. Figure 1 illustrates the type of information that ultrasound can obtain about the constituent tissues of the breast. Ultrasound will not 146
F I G U R E 2. Two transverse sections through the abdomen. The stdmach and the duodenum are filled with methylcellulose.
replace xeroradiography, as current results indicate that the techniques are complementary. Ultrasound works best in the young breast in which the low level of echoes associated with malignant changes is more readily visualized in the complex of stronger echoes obtained from glandular tissue. Xeroradiography , on the other hand, works best in the older breast where the large amount of fat infiltration makes the changes associated with malignancy more difficult t o determine by ultrasound. If ultrasound can identify high-risk patients, they could then be examined regularly by ultrasound or other methods such as thermography and xeroradiography. Potentially, ultrasound may also be developed to show premalignant changes in the breast, which would open up a new vast area of application. By 1980, the examination of the stomach will become of major interest. Work at the Royal Hospital for Women, Sydney has demonstrated that, much like using the full bladder t o lift the uterus above the symphysis pubis, filling the stomach and the duodenum with an inert J O U R N A L O F CLINICAL U L T R A S O U N D
F I G U R E 3. Two horizontal sections of brain of a 2 weeks old infant with moderate hydrocephaly,
liquid may be used t o push the bowel out of the way t o create an acoustic window. This allows the examination of organs such as the pancreas, which are often shadowed by these air-filled structures. An ingested methyl cellulose suspension produces small echoes that allow demonstration of the outlines of the stomach wall, particularly the anterior wall which is difficult to visualize by radiography. Figure 2 shows two transverse sections through the abdomen of a patient. The figure illustrates the type of detail that can be obtained from the stomach, the duodenum, and posterior structures. The examination of the stomach is more easily performed on a prone patient, as any remaining air in the stomach floats into the fundus or abuts the posterior wall. In the supine position, the remaining air floats against the anterior wall and shadows all posterior information. By 1980, pediatric echography will also be more extensively used. In some applications the examination will use the experience developed in adults with the extra requirements necessary for the visualization of similar but smaller structures in .the infant. Other applications, such as examination of the brain, will be unique to pediatrics. The less ossified skull of infants does not impede t o the same extent the passage of ultrasound and this allows the visualization of detail which rivals that obtained by computerized tomography without the necessity of exposing the infant to ionizing radiation or anesthesia. Figure 3 is an example of two head echograms showing enlarged lateral and third ventricles in a young infant with moderate hydrocephaly. Similarly in infants, the bony sternum and the ribs do not impede t o the same extent the passage of ultrasound and the cross-sectional examination the breast and mediastinum will provide unique diagnostic information. In the early eighties, our interest will also center on the measurement of blood flow in deep vessels. Preliminary results on the marriage of VOLUME 6 . NUMBER 3
Average velocity
C jD
=
-
2f*COS0
F I G U R E 4. Combined B mode and pulsed doppler method for quantitative measurement of blood flow in umbilical vein of fetus.
B mode echography with pulsed Doppler has shown that, by combining these two methods, one can identify and measure the diameter of vessels, select the optimum line of sight, and by picking only the Doppler frequency shift signal originating from the selected area, measure quantitatively the blood flow in that vessel. We have performed quantitative measurements of blood flow in the fetal umbilical vein and in the right branch of the portal vein. The application of the method is illustrated in Figure 4 and some of the measured values are shown in Table I. Note that the umbilical blood flow in fetus of various gestational ages appears constant at 105 ml/min/kg fetal weight. It is probably unwise to speculate on developments that are likely t o occur in the later eighties. I suspect that tissue characterization studies will have come into their own and that the increased range of application studies will have opened new frontiers in ultrasonic examination. For instance, tissue characterization of fetal lung development would open up a new and broad field of application in obstetrics that would allow us t o dispense with amniocentesis and the lecithin sphingomyelin ratio test to estimate fetal maturity. 147
TABLE I Gestational Age weeks
25% 28 30 % 30% 35 36 36 36% 37 37 Y 2 38 % 40
Weight of Fetus Kg
Diameter of Vein mm
Average Velocity cm sec-1
Flow in Vein mi min-1
ml min-lkg-1
0.88 1.I 1.4 1.4 2.4 2.6 2.6 2.7 2.8 2.9 3 .O 3.2
5.0 6.5 6.3 6.0 7.5 7.5 7.3 6.6 9.0 8.2 6.6 8.5
8.4 6.3 6.7 9.7 11.2 9.4 8.3 17 6.1 8.0 16.0 9.8
99 125 125 165 297 249 208 349 233 253 328 334
112 114 90 118 126 96 80 129 83 87 109 104
No discussion of the future role of diagnostic ultrasound would be complete without some mention of the impact that computerized tomography (CT) has made on organ imaging. Before the advent of CT and to a lesser extent of gray scale echography, a relatively clear distinction existed between the roles of radiology, nuclear medicine, and ultrasound. Radiology was used primarily to examine highcontrast structures. It produced projected views of the examined organs. Nuclear medicine also provided projected views, but the resolution of the images was relatively poor and the technique was used primarily to determine the functional status of tissue. Ultrasound bridged those two disciplines and provided cross-sectional views of soft-tissue organs. The situation has now changed dramatically. Xray and nuclear CT provides cross-sectional views of soft-tissue organs while gray scale visualizes the texture of tissues seen as hot or cold spots on nuclear scans. Doppler ultrasound provides functional blood flow information. Thus the distinction between anatomy and function has become blurred, and I believe it is more appropriate to refer to the actual parameters of tissues that are measured by the three specialties, namely the xray absorption in radiology, the uptake of radiopharmaceutical agents in nuclear medicine, and the acoustic reflectivity and attentuation of ultrasound. These three basic properties of tissue are independent, and it is unlikely that any one technique will supplement the other. Nevertheless the high cost of the equipment and the enthusiasm that has accompanied the purchase of CT equipment has attracted the attention of administrators who have the respon148
Flow/Weight
sibility for the distribution of medical funds. Recommendations are establishing scientific investigations to determine the role of the various modalities to assure optimum utilization of the finite resources that exist in all countries for the provision of patient care. The political pressures generated by these factors may force the creation of organ imaging centers where the referring physician, in consultation with the organ imaging specialist, will decide which test should be employed t o obtain the necessary diagnostic information at minimum cost to the community. Because the different skills that exist in radiology, nuclear medicine, and ultrasound are likely to become more complex, it is unlikely that there will be a sufficient number of organ imaging specialists who will have sufficient expertise in all three fields. One approach that is being adopted in some hospitals in Australia has been the establishment of organ imaging centers consisting of the departments of radiology, nuclear medicine, and ultrasound. The independent status of the three specialties is respected; but common requirements are pooled to minimize cost. Although diagnostic ultrasound is now an established, rapidly expanding, special branch of medical practice, diagnostic ultrasound is limited because no certificates of professional competence are issued nor is the specialty recognized as such by the medical authorities. Recognizing these limitations and being aware of the types of abuses that could result if these deficiencies were not corrected, the Australian Society for Ultrasound in Medicine and Biology has in the past year initiated action that should help to overcome some of these difficulties. The J O U R N A L O F CLINICAL ULTRASOUND
Australian Society is a body similar t o the AIUM. It is a professional society of investigators interested in advancing the knowledge and application of diagnostic ultrasound. The Society a t present has over 350 members. Approximately 250 of these are medical practitioners, and 60% are radiologists. In September 1976, following a motion passed at its general meeting, the Society looked a t the various areas of applications covered by ultrasound and a t the specialties in Australia that provide training in ultrasound. At a special meeting held three months later, it was unanimously agreed that, due t o the broad area of medical specialties that employ ultrasound and the paucity of training provided by the existing specialties, ultrasound was not directly related t o any one specialty and that the only national body in Australia with expertise in the field was the Australian Society itself. It was then moved that the Society should establish a standard of training required for the practice of diagnostic ultrasound and that this would be best served by establishing the Diploma of Diagnostic Ultrasound which would be open to medical practitioners registered in Australia and New Zealand. The qualifications for the Diploma were to be similar to those which currently apply to other specialties. Exemptions were created for candidates who already hold specialist qualifications in radiology, nuclear medicine, obstetrics and gynecology, surgery, general medicine, cardiology, and ophthalmology. These candidates could apply for examination for the Diploma after two years of experience in ultrasound. A Board of Examiners was set up and invitations for foundation memberships were announced. Eighty-five applications were received for foundation membership. The Board of Examiners of the Society elected that the Foundation Diploma be awarded to 46 applicants. Nineteen applicants were invited to take the examination
V O L U M E 6. N U h l B E R 3
later in the year and another 25 applicants were invited t o take the examination next year. The examinations of the first 19 applicants were held in June 1977 and the Diploma was awarded to 17 candidates. Six of these were cardiologists. Since then, 20 more applications for examinations have been received. By late 1978 it is likely that over 100 Diplomas will have been awarded. If one considers that the population of Australia is a fifteenth that of the USA, similar action by an appropriate body in the USA would award over 1,500 Diplomas t o US medical practitioners with experience in diagnostic ultrasound. The Australian Society has also approached the National Specialist Qualification Advisory Committee of Australia t o recognize diagnostic ultrasound as a medical specialty. The application is under review and a decision on the matter will be made later this year. The Australian Society also has a sonographers' section similar to ASU'l'S, and the question of certification of sonographers is also being considered. As yet this application is not as fully developed, as it was considered that the certification of medical practitioners was by far the more pressing issue. The Australian Society is closely following the action of ASUTS on this subject and will probably adopt many of the requirements recommended by ASUTS . In summary it is clear that over the last 25 years diagnostic ultrasound has developed into a major specialty and that this specialty will continue t o grow. Many of us in Australia consider that as more medical practitioners take up ultrasound on a full time basis, a critical number of people will be reached that will ensure that ultrasound will become recognized as a new medical specialty. We believe that this development, when coordinated and integrated with other specialties, will improve the practice of organ imaging and thus contribute in real terms t o t h e quality of care provided to the patient. 4~
149
