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Obstetrics and perinatology
Ultrasound in Med. & Biol., Vol. 26, Supplement 1, pp. S82–S84, 2000 Copyright © 2000 World Federation for Ultrasound in Medicine & Biology Printed in the USA. All rights reserved 0301-5629/00/$–see front matter
PII S0301-5629(00)00173-3
● Part II: Clinical Applications OBSTETRICS AND PERINATOLOGY ROY A. FILLY* and LAWRENCE D. PLATT† *Department of Radiology, University of California, San Francisco, California, USA; and †Department of Obstetrics and Gynecology, Cedars-Sinai Medical Center, Los Angeles, California, USA
INTRODUCTION
going education of the physicians and the appropriate use of and supervision of sonographers. The role of accreditation of practices such as those directed by the American Institute of Ultrasound in Medicine or the American College of Radiology seems critical in assuring the patient’s best interest.
Sonography was first considered for use in pregnant women because the acoustic energy employed to visualize the interior of the uterus appeared safe for the fetus. Now, after decades of study, that presumption appears to have been correct, as sonographic energy continues to demonstrate a high benefit/risk factor in obstetrical imaging. To date, there have been no reproducible bioeffects on the human fetus arising from the use of diagnostic ultrasound (US). However, it is sonography’s remarkable image quality and not its safety record that has revolutionized modern obstetrical care. Sonography has been so safe (without bioeffects) and helpful in obstetrical management that the indications for acoustic imaging are extremely liberal and are routine in many countries, but there are still no mandates for routine US. More than 95% of pregnant Americans desire sonography during their pregnancy (Kazerooni et al. 1997). Their reasons vary. Some want to know the gender of the fetus. Some just want to “see” the fetus. All want whatever information they can gather that increases their confidence that the fetus is “OK.”
TECHNOLOGY The technological fronts on which obstetrical sonography will undoubtedly make significant advances in the future are: tissue harmonic imaging, contrast agents, and three-dimensional (3-D) imaging. Also, the field will advance through analysis of sonographic results compared to other imaging modalities (specifically magnetic resonance imaging, MRI). We will discuss the last one first. When computed body tomography (CT) arrived, many thought that it would result in the demise of abdominal sonography. This did not occur. Instead, there were two different results. First, clinicians developed an increased awareness and confidence in sonography. They were more easily able to understand sonographic images by comparing them to the more intuitively interpreted CT scans. Second, sonographic practitioners benefited from the ability to compare the results of the two modalities, greatly accelerating their learning curve for the interpretation of abdominal sonograms. To date, we have had no serious contender to compete with sonography in obstetrical imaging. Now, magnetic resonance imaging (MRI) will assume this role. We anticipate a rapid learning curve in our ability to interpret obstetrical sonograms as we compare the sonographic results with the MRI results. Other practitioners, it stands to reason, will similarly benefit. Although we can anticipate that advancements enabling increasingly rapid acquisition of MR images will quickly carry this technology into the world of obstetrical imaging (Levine et al. 1998), MRI will undoubtedly continue to have a secondary role to ultrasonic imaging.
TRAINING Unfortunately, the solace and assurance they seek may not be forthcoming from their “screening sonogram.” It is ironic, indeed, that this increasingly sophisticated technology is often performed by marginally trained practitioners (Clair et al. 1992; Ewigman et al. 1993). If the patient is ever going to benefit appropriately from advancements in acoustic imaging technology, the future of obstetrical sonography must first address problems in training, rather than simply focusing on new sonographic tools. This would include the issues of on-
Address correspondence to: Dr. Roy A. Filly, Department of Radiology, University of California, San Francisco, 505 Parnassus Avenue, L-374, San Francisco, CA 94143-0628 USA. S82
Obstetrics and Perinatology ● R.A. FILLY
Harmonic imaging, recently introduced, has already revolutionized obstetrical imaging. We now use it in virtually every scanning situation, to the exclusion of fundamental beam reflection. This technique “looks” at the acoustic signals generated in tissue by the insonating beam, rather than the reflected wave of the insonating beam. The effect is greatly to reduce the distortion caused as sound passes through the abdominal wall. Therefore, it works best in those patients who have previously been the most difficult to scan (i.e., obese patients). Harmonic imaging produces an easily visible and significant improvement in signal-to–noise ratio. Refinements and embellishments of this technology could remarkably improve the quality of ultrasonic images. Even in its current state, we consider harmonic imaging to be among the most significant technical advancements since color Doppler sonography. Sonologists are currently evaluating commercially available contrast agents (Schmiedl et al. 1998). Contrast agents will undoubtedly have a dramatic impact on acoustic imaging. Imagine CT without iodinated contrast agents and MRI without gadolinium contrast agents. The day will come, probably within the next decade, when sonologists will have equivalent image-enhancing agents. No other event, in our opinion, will have a more profound effect on the future of sonographic imaging. Unfortunately, although useful, we do not believe this remarkable future will come from the microbubble contrast agents currently available or from enhancements of these products (other aspects of harmonic imaging may alter this conclusion) (Burns 1996). Sonologists need an agent that produces similar effects as iodinated contrast agents in computed tomography. When that product arrives, every attitude toward US in clinical imaging will require reevaluation. Contrast agents will probably not alter fetal imaging to any great extent. However, placental imaging may be greatly improved for the detection of infarction and abruption. The potential fetal effects of some contrast agents have and will continue to have a negative impact on their development for and use in pregnancy. 3-D ultrasonography in obstetrical imaging is showing progressive improvements in speed, image quality and affordability (Johnson et al. 1997). This new technology will undoubtedly have a dramatic impact on obstetrical imaging. The magnitude of the impact is, as yet, difficult to predict. However, if volume imaging (inherent to 3-D imaging) with later computer reconstruction of images approaches the image quality that can be obtained by selectively moving the transducer over the body surface, selecting an appropriate image, then freezing and storing the image (i.e., the current “fluoroscopic” method), we believe this will completely replace our current methodology.
AND
L.D. PLATT
S83
Nothing that we have seen before would do more to decrease the perception that sonography is highly operator-dependent. Volume imaging could, as well, greatly improve the precision of fetal weight estimation. Additionally, the use of surface rendering will play an important role in syndrome recognition. Of late, the incorporation of 3-D into clinical and research practices appears to be at a rate similar to or in excess of that seen with real-time scanning. CONCLUSIONS Undoubtedly, advances in US have played the most dramatic role in the field of perinatal medicine. The ability not only to make in utero diagnosis, but also to use ultrasound to direct in-utero treatment has been nothing short of revolutionary. Landmark diagnosis of fetal abnormalities, such as anecephaly, to current techniques in diagnosing congenital heart defects have changed the course of obstetrical management. The role of US role in fetal blood sampling via “PUBS” opened this route to the fetus by at least a 1000-fold over fetoscopy. Its role in evaluating the Rhsensitized fetus by direct blood sampling to IV transfusion has led to dramatic increases in survival in these cases. The use of US to help evaluate the risk of fetal aneuploidy has helped many women avoid invasive testing, and moving away from age alone risk adjustments to those incorporating multiple ultrasound markers in the first and second trimester has become standard. If risks for aneuploidy remain high, ultrasound has proven valuable at the time of invasive testing (CVS, amniocentesis) and the complication rates for these procedures have been dramatically reduced. Perinatal medicine in the new millennium would be nowhere without ultrasound. Although in-utero diagnosis of fetal malformations often places patients in positions of quandary and hopelessness, newer uses of US help to guide treatments, such as placement of vesico-amniotic shunts in cases of bladder neck obstruction, have proven invaluable. Its role in prediction of preterm labor by cervical length measurement has led to decreased perinatal mortality. Although hardly an exact science, US assessment of fetal age and weight has also contributed to this reduction in fetal morbidity. Perhaps, as stated earlier, 3-D US has the potential to improve fetal weight evaluation to an even greater degree. While ultrasound has been regularly used for fetal dating, placental location and fetal anatomy surveys, its role in evaluation of fetal well-being is widely known. The development of the fetal biophysical profile some 20 y ago has proven invaluable in helping the clinician to assess whether leaving the fetus in-utero an elective delivery is appropriate. Although Doppler
S84
Ultrasound in Medicine and Biology
is addressed elsewhere, its role in perinatal medicine must be emphasized. Whether it is used to screen uterine arteries for the risk of PIH and/or intrauterine growth retardation (IUGR) or to screen the umblical arteries for IUGR, many studies have demonstrated its utility is highest in the assessment of the growthrestricted fetus. The application of Doppler in other vessels, particularly in the central nervous system (middle cerebral arteries), has also been shown to be invaluable. In summary, perinatal medicine has dramatically changed since the introduction of US. From early firsttrimester diagnosis of malformation through late pregnancy fetal assessment, to the new uses in open fetal surgery, US has been the common denominator in allowing us to treat the fetus as a patient.
Volume 26, Supplement 1, 2000
REFERENCES Burns PN. Harmonic imaging with ultrasound contrast agents. Clin Radiol 1996; 51 Supp.1 :50 –55. Clair MR, Kessler HB, Pasto M, et al. US Healthcare (HMO PA/NJ) obstetrical ultrasound quality assurance program. Radiology 1992; 185(P):143. Ewigman BG, Crane JP, Frigoletto FD, et al. Effect of prenatal ultrasound screening on perinatal outcome: RADIUS study. N Engl J Med 1993; 329: 821– 827. Johnson DD, Pretorius DH, Riccabona M, et al. Three dimensional ultrasound of the fetal spine. Obstet Gynecol 1997;89:434 – 438. Kazerooni EA, Trever K, Bree RL, et al. Patients’ perception on the use of screening ultrasound during pregnancy. Radiology 1997:205(P): 224 –225. Levine D, Barnes PD, Sher S, et al. Fast fetal MR imaging: reproducibilty, technical quality, and conspicuity of anatomy. Radiology 1998;206:549 –554. Schmiedl UP, Komarniski K, Winter TC, et al. Assessment of fetal and placental blood flow in primates using contrast enhanced ultrasonography. J Ultrasound Med 1998;17:75– 80.
PII S0301-5629(00)00173-3
● Part II: Clinical Applications OBSTETRICS AND PERINATOLOGY ROY A. FILLY* and LAWRENCE D. PLATT† *Department of Radiology, University of California, San Francisco, California, USA; and †Department of Obstetrics and Gynecology, Cedars-Sinai Medical Center, Los Angeles, California, USA
INTRODUCTION
going education of the physicians and the appropriate use of and supervision of sonographers. The role of accreditation of practices such as those directed by the American Institute of Ultrasound in Medicine or the American College of Radiology seems critical in assuring the patient’s best interest.
Sonography was first considered for use in pregnant women because the acoustic energy employed to visualize the interior of the uterus appeared safe for the fetus. Now, after decades of study, that presumption appears to have been correct, as sonographic energy continues to demonstrate a high benefit/risk factor in obstetrical imaging. To date, there have been no reproducible bioeffects on the human fetus arising from the use of diagnostic ultrasound (US). However, it is sonography’s remarkable image quality and not its safety record that has revolutionized modern obstetrical care. Sonography has been so safe (without bioeffects) and helpful in obstetrical management that the indications for acoustic imaging are extremely liberal and are routine in many countries, but there are still no mandates for routine US. More than 95% of pregnant Americans desire sonography during their pregnancy (Kazerooni et al. 1997). Their reasons vary. Some want to know the gender of the fetus. Some just want to “see” the fetus. All want whatever information they can gather that increases their confidence that the fetus is “OK.”
TECHNOLOGY The technological fronts on which obstetrical sonography will undoubtedly make significant advances in the future are: tissue harmonic imaging, contrast agents, and three-dimensional (3-D) imaging. Also, the field will advance through analysis of sonographic results compared to other imaging modalities (specifically magnetic resonance imaging, MRI). We will discuss the last one first. When computed body tomography (CT) arrived, many thought that it would result in the demise of abdominal sonography. This did not occur. Instead, there were two different results. First, clinicians developed an increased awareness and confidence in sonography. They were more easily able to understand sonographic images by comparing them to the more intuitively interpreted CT scans. Second, sonographic practitioners benefited from the ability to compare the results of the two modalities, greatly accelerating their learning curve for the interpretation of abdominal sonograms. To date, we have had no serious contender to compete with sonography in obstetrical imaging. Now, magnetic resonance imaging (MRI) will assume this role. We anticipate a rapid learning curve in our ability to interpret obstetrical sonograms as we compare the sonographic results with the MRI results. Other practitioners, it stands to reason, will similarly benefit. Although we can anticipate that advancements enabling increasingly rapid acquisition of MR images will quickly carry this technology into the world of obstetrical imaging (Levine et al. 1998), MRI will undoubtedly continue to have a secondary role to ultrasonic imaging.
TRAINING Unfortunately, the solace and assurance they seek may not be forthcoming from their “screening sonogram.” It is ironic, indeed, that this increasingly sophisticated technology is often performed by marginally trained practitioners (Clair et al. 1992; Ewigman et al. 1993). If the patient is ever going to benefit appropriately from advancements in acoustic imaging technology, the future of obstetrical sonography must first address problems in training, rather than simply focusing on new sonographic tools. This would include the issues of on-
Address correspondence to: Dr. Roy A. Filly, Department of Radiology, University of California, San Francisco, 505 Parnassus Avenue, L-374, San Francisco, CA 94143-0628 USA. S82
Obstetrics and Perinatology ● R.A. FILLY
Harmonic imaging, recently introduced, has already revolutionized obstetrical imaging. We now use it in virtually every scanning situation, to the exclusion of fundamental beam reflection. This technique “looks” at the acoustic signals generated in tissue by the insonating beam, rather than the reflected wave of the insonating beam. The effect is greatly to reduce the distortion caused as sound passes through the abdominal wall. Therefore, it works best in those patients who have previously been the most difficult to scan (i.e., obese patients). Harmonic imaging produces an easily visible and significant improvement in signal-to–noise ratio. Refinements and embellishments of this technology could remarkably improve the quality of ultrasonic images. Even in its current state, we consider harmonic imaging to be among the most significant technical advancements since color Doppler sonography. Sonologists are currently evaluating commercially available contrast agents (Schmiedl et al. 1998). Contrast agents will undoubtedly have a dramatic impact on acoustic imaging. Imagine CT without iodinated contrast agents and MRI without gadolinium contrast agents. The day will come, probably within the next decade, when sonologists will have equivalent image-enhancing agents. No other event, in our opinion, will have a more profound effect on the future of sonographic imaging. Unfortunately, although useful, we do not believe this remarkable future will come from the microbubble contrast agents currently available or from enhancements of these products (other aspects of harmonic imaging may alter this conclusion) (Burns 1996). Sonologists need an agent that produces similar effects as iodinated contrast agents in computed tomography. When that product arrives, every attitude toward US in clinical imaging will require reevaluation. Contrast agents will probably not alter fetal imaging to any great extent. However, placental imaging may be greatly improved for the detection of infarction and abruption. The potential fetal effects of some contrast agents have and will continue to have a negative impact on their development for and use in pregnancy. 3-D ultrasonography in obstetrical imaging is showing progressive improvements in speed, image quality and affordability (Johnson et al. 1997). This new technology will undoubtedly have a dramatic impact on obstetrical imaging. The magnitude of the impact is, as yet, difficult to predict. However, if volume imaging (inherent to 3-D imaging) with later computer reconstruction of images approaches the image quality that can be obtained by selectively moving the transducer over the body surface, selecting an appropriate image, then freezing and storing the image (i.e., the current “fluoroscopic” method), we believe this will completely replace our current methodology.
AND
L.D. PLATT
S83
Nothing that we have seen before would do more to decrease the perception that sonography is highly operator-dependent. Volume imaging could, as well, greatly improve the precision of fetal weight estimation. Additionally, the use of surface rendering will play an important role in syndrome recognition. Of late, the incorporation of 3-D into clinical and research practices appears to be at a rate similar to or in excess of that seen with real-time scanning. CONCLUSIONS Undoubtedly, advances in US have played the most dramatic role in the field of perinatal medicine. The ability not only to make in utero diagnosis, but also to use ultrasound to direct in-utero treatment has been nothing short of revolutionary. Landmark diagnosis of fetal abnormalities, such as anecephaly, to current techniques in diagnosing congenital heart defects have changed the course of obstetrical management. The role of US role in fetal blood sampling via “PUBS” opened this route to the fetus by at least a 1000-fold over fetoscopy. Its role in evaluating the Rhsensitized fetus by direct blood sampling to IV transfusion has led to dramatic increases in survival in these cases. The use of US to help evaluate the risk of fetal aneuploidy has helped many women avoid invasive testing, and moving away from age alone risk adjustments to those incorporating multiple ultrasound markers in the first and second trimester has become standard. If risks for aneuploidy remain high, ultrasound has proven valuable at the time of invasive testing (CVS, amniocentesis) and the complication rates for these procedures have been dramatically reduced. Perinatal medicine in the new millennium would be nowhere without ultrasound. Although in-utero diagnosis of fetal malformations often places patients in positions of quandary and hopelessness, newer uses of US help to guide treatments, such as placement of vesico-amniotic shunts in cases of bladder neck obstruction, have proven invaluable. Its role in prediction of preterm labor by cervical length measurement has led to decreased perinatal mortality. Although hardly an exact science, US assessment of fetal age and weight has also contributed to this reduction in fetal morbidity. Perhaps, as stated earlier, 3-D US has the potential to improve fetal weight evaluation to an even greater degree. While ultrasound has been regularly used for fetal dating, placental location and fetal anatomy surveys, its role in evaluation of fetal well-being is widely known. The development of the fetal biophysical profile some 20 y ago has proven invaluable in helping the clinician to assess whether leaving the fetus in-utero an elective delivery is appropriate. Although Doppler
S84
Ultrasound in Medicine and Biology
is addressed elsewhere, its role in perinatal medicine must be emphasized. Whether it is used to screen uterine arteries for the risk of PIH and/or intrauterine growth retardation (IUGR) or to screen the umblical arteries for IUGR, many studies have demonstrated its utility is highest in the assessment of the growthrestricted fetus. The application of Doppler in other vessels, particularly in the central nervous system (middle cerebral arteries), has also been shown to be invaluable. In summary, perinatal medicine has dramatically changed since the introduction of US. From early firsttrimester diagnosis of malformation through late pregnancy fetal assessment, to the new uses in open fetal surgery, US has been the common denominator in allowing us to treat the fetus as a patient.
Volume 26, Supplement 1, 2000
REFERENCES Burns PN. Harmonic imaging with ultrasound contrast agents. Clin Radiol 1996; 51 Supp.1 :50 –55. Clair MR, Kessler HB, Pasto M, et al. US Healthcare (HMO PA/NJ) obstetrical ultrasound quality assurance program. Radiology 1992; 185(P):143. Ewigman BG, Crane JP, Frigoletto FD, et al. Effect of prenatal ultrasound screening on perinatal outcome: RADIUS study. N Engl J Med 1993; 329: 821– 827. Johnson DD, Pretorius DH, Riccabona M, et al. Three dimensional ultrasound of the fetal spine. Obstet Gynecol 1997;89:434 – 438. Kazerooni EA, Trever K, Bree RL, et al. Patients’ perception on the use of screening ultrasound during pregnancy. Radiology 1997:205(P): 224 –225. Levine D, Barnes PD, Sher S, et al. Fast fetal MR imaging: reproducibilty, technical quality, and conspicuity of anatomy. Radiology 1998;206:549 –554. Schmiedl UP, Komarniski K, Winter TC, et al. Assessment of fetal and placental blood flow in primates using contrast enhanced ultrasonography. J Ultrasound Med 1998;17:75– 80.