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OBJECTIVE To compare the effectiveness of the PAPNET System with conventional rescreening of negative cervical smears in a high-risk population. STUDY DESIGN Three thousand ninety-seven negative cervical smears from women with past history of cervical abnormalities were rescreened manually and with the PAPNET System. There were two reviews of PAPNET images: the first by two cytotechnologists with limited exposure to the instrument, and the second, limited to smears with discrepant diagnoses, by an expert in the use of the system. The remaining discrepant smears were submitted to a blinded microscopic review by a third party. The a priori consensus diagnosis was arbitrarily established when the result of two of the three reviews--manual, PAPNET and the independent third review--were concordant. The results of rescreening were compared with available biopsies. RESULTS On manual rescreening of the 3,097 smears, 2,901 (93.66%) were reported as negative and 170 (5.49%) as abnormal. On the first PAPNET review, 2,938 (94.87%) were reported as negative and 150 (4.84%) as abnormal. There were 144 smears with discrepant diagnoses. After the second PAPNET review of these discrepant smears, the agreement between manual and PAPNET rescreening rose from 94.27% to 95.58%. A final, blinded review of 89 residual discrepant smears was used to establish consensus diagnoses. The diagnoses made by PAPNET-assisted rescreening agreed much better with the consensus diagnoses than did manual rescreening (Kappa = .61 vs. Kappa = -.32, P < .001). When compared with the results of 50 available biopsies, PAPNET-assisted rescreening also had a somewhat lower false negative rate (sensitivity 58.82% vs. 41.18%, P = .17) and a statistically significant lower false positive rate (specificity 63.64% vs. 36.36%, P = .01). CONCLUSION PAPNET-assisted rescreening, when carried out by an experienced person, is more efficient than manual rescreening.

Objective: Cervicography was evaluated as a primary screening method for cervical cancer. Study Design: Cervigrams of 8460 women were taken on enrollment into a population-based study of cervical neoplasia. Cervicography results were compared with a referent diagnosis determined by histologic analysis and 3 cytologic tests, and with the performance of conventional cytologic evaluation. Results: Cervicography identified all 11 cancers, whereas cytologic testing missed 1. Cervicography yielded sensitivities for detecting high-grade squamous intraepithelial lesions or cancer of 49.3% overall (specificity, 95.0%), 54.6% in women younger than 50 years of age, and 26.9% in women 50 years of age and older. Cytologic testing yielded sensitivities for detecting high-grade squamous intraepithelial lesions or cancer of 77.2% overall (specificity, 94.2%), 75.5% in women younger than 50 years of age, and 84.6% in women 50 years of age and older. Conclusions: Cytologic testing performed better than cervicography for the detection of high-grade squamous intraepithelial lesions. Cervicography performed marginally better than cytologic testing for the detection of invasive cervical cancer. Cervicography is not recommended for postmenopausal women. (Am J Obstet Gynecol 1999;180:290-8.)

BACKGROUND Automated cytology devices have utility in quality assurance applications, but the effectiveness of these devices in primary screening is unknown. METHODS Enrollment smears obtained from 7323 women participating in a population-based study sponsored by the National Cancer Institute were screened manually in Costa Rica and then evaluated independently in the U.S. with the PAPNET system (Neuromedical Systems, Inc., Suffern, NY), a semiautomated, neural network-based device. Smears with abnormal PAPNET images were microscopically rescreened and then diagnosed by a U.S. cytopathologist. ThinPrep slides (Cytyc Corporation, Boxborough, MA), prepared from rinses of the cytologic sampler, and cervigrams (National Testing Laboratories, Fenton, MO) were also evaluated. Women with any abnormal cytologic diagnosis or a positive cervigram were referred for colposcopy with biopsy and definitive therapy if indicated. RESULTS Based on the U.S. cytotechnologist's review of the PAPNET images, 1017 (13.9%) of 7323 smears were selected for manual screening, resulting in the selection of 492 (6.7%) possibly abnormal slides for referral to the U.S. pathologist. Ultimately, 312 smears (4.3% of the total) were diagnosed as containing squamous cells of undetermined significance or a more severe abnormality (≥ASCUS), resulting, hypothetically, in the referral of 66.5% of women with a final diagnosis of a squamous intraepithelial lesion or a more severe abnormality (≥SIL) and 86.0% of patients with ≥high grade SIL. Conventional microscopic screening performed in Costa Rica resulted in the hypothetical referral of 6.5% of patients with ≥ASCUS for colposcopy, including 69.5% of patients with ≥SIL and 79.8% of those with ≥high grade SIL. CONCLUSIONS In this study, PAPNET-assisted cytologic screening accurately identified smears obtained from women with high grade SIL or carcinoma. Determination of the clinical cost-effectiveness of PAPNET-assisted screening in routine practice awaits future study. [See editorial on pages 269-72, this issue.] Cancer (Cancer Cytopathol) 1998;84:273-280. © 1998 American Cancer Society.

Issues Computerized technologies probably will revolutionize the field of gynecologic cytology in the next century. Such technologies will be useful in both training and evaluating proficiency. However, manual screening/review of gynecologic cytology preparations is the current "gold standard" for both training and assessment of proficiency. Consensus position Training programs for cytotechnologists and pathologists should provide instruction and experience in new technologies, but their introduction may depend on the availability of equipment and staff. Advantages of digital images for training include standardization of teaching sets and interactive capabilities, allowing educational feedback. Computerized support/assistance devices aid in complete screening of the slide during training and provide feedback to cytologists on screening techniques. Liquid-based cytopreparatory instruments facilitate multiple glass slides for teaching or testing. Proficiency testing (PT) in cytology has similar quality assurance goals as in other areas of the laboratory, but the subjective nature of cytologic analysis poses many challenges for implementation. There is consensus that all cytology practitioners would like to know the proficiency of the laboratory. However, the majority question the value and validity of any large-scale formal testing programs. Locator and diagnostic skills are both critical in cytology, but assessment of each skill may occur in different ways using computerized technologies. Any type of assessment should provide educational feedback to participants. Psychometric issues in PT include the consideration of different types of validity, including face, content, construct and criterion related. The reliability or consistency of the testing event is also critical. A valid and reliable correlation between work performance and performance on a PT needs to be established. The goal is to ensure that PT will identify submarginal practitioners and that persons successful on PT are in fact competent. Any cytology PT program should also be considered in the context of other laboratory quality assurance tools and the entire cervical cancer screening program. Regulatory agencies should evaluate entire laboratory performance, while each laboratory director should assume primary responsibility for evaluating and documenting the competency and daily performance of each practicing cytologist. Professional scientific organizations should take the lead in recommending methods and standards of performance assessment. Ongoing issues A reliable method of correlating daily competency with results on PT is not yet established. Methods may evolve ever time using new technologies. The use of computerized techniques and images for assessment will require careful deliberation by experts as well as validation by practicing cytologists. Variables include diagnostic categories for testing, numbers of challenges per testing event, types of slide preparations and characteristics of the digital images. Availability of equipment and staff will affect the introduction of new technologies in different regions.

Issues Cell Preparation Methods Standardized fixation and optimal staining Sampling of cervix, sampling error, homogenization of sample, subsampling Assessment of liquid-based preparations: efficacy and economic impact Training and transitional procedures before full implementation of new technologies Criteria for Sample Adequacy Clinician responsibility for collecting and providing representative sample to laboratory Collection instruments, number of slides Cellular content of samples: evidence of transformation zone (TZ) sampling, number of squamous cells present, obscuring factors Screening issues CONSENSUS POSITION The conventional cervical smear remains the standard method of cervical cancer screening but has limitations in individual test sensitivity and specificity. Sample takers should: (1) receive appropriate training in sample collection, (2) be held responsible for providing the laboratory with appropriate samples, and (3) have their performance monitored. The instruments used for sampling should collect cells from both the ectocervix and endocervix; optimally, TZ sampling, represented by the presence of endocervical or squamous metaplastic cells, should be identifiable in samples other than atrophic specimens. The adequacy of a specimen (as judged microscopically) does not guarantee that it is representative of the cervix. Each cytology report should include a comment on cellular content/adequacy of the specimen. Liquid-based preparations may overcome many of the inherent problems with the conventional cervical smear. Ongoing issues We need further data on the cost-effectiveness of making two slides from cervical specimens and/or using two samplers rather than a single one. Do we have enough information to make recommendations as to the appropriate type of sampler to be used in particular situations, such as routine screening? What is the best method of screening for/detecting endocervical glandular neoplasia? How are such terms as unsatisfactory and inadequate defined in cervical cytology classifications other than the Bethesda System? What number and types of epithelial cells should be present (visualized) in a cervical smear or liquid-based preparation for it to be considered adequate? Do we need to have evidence of TZ sampling in specimens taken during the follow-up period after treatment of squamous intraepithelial lesion or after detection of endocervical glandular neoplasia? What criteria for obscuring factors, such as blood and inflammation, should be used in assessing adequacy? Cost-benefit analyses of utilizing liquid-based preparations are needed. Should we inform women about the technical details of the test methods available or chosen by the laboratory? Are women in a position to decide which method is the most appropriate to assess their cervical scrape sample? We need to obtain more information about the properties of proprietary liquid fixative/transport media with respect to inactivation of viral pathogens, tuberculosis and other bacterial pathogens and suitability for immunobiologic and molecular tests, etc. We need to obtain more information on the use of stoichiometric stains and the limitations of Papanicolaou stain for image analysis systems. The use of liquid-based preparations for nongynecologic cytopathology and ancillary tests must be considered, including criteria for adequacy. We need to obtain more information on the time required for and best methods of training experienced cytotechnologists to become competent at assessing liquid-based cervical preparations.

OBJECTIVE: To provide effectiveness metrics for the clinical utility of an interactive, neural network-assisted (INNA) system by compiling results from clinical studies, classifying them according to a systematic protocol and pooling data from comparably designed studies. STUDY DESIGN: This investigation synthesized evidence from published and recently completed, unpublished clinical reports evaluating INNA screening. Using a taxonomy developed to classify study results, effectiveness estimates were derived by pooling results according to similarity of study design and effectiveness metric. RESULTS: INNA sensitivity estimates range from 89% to 100%, assuming an 85% baseline sensitivity for unassisted screening. Relative yield metrics for INNA rescreening effectiveness range from 1.08 to 1.49, resulting in overall sensitivity estimates of 92-100% when applied to a baseline sensitivity of 85%. Estimates for another relative yield metric, representing INNA use in a primary screening mode (non-United States studies), show 1840% increases in the yield of abnormality with INNA screening when compared with unassisted screening alone. CONCLUSION: The findings of this investigation indicate that a relatively extensive evidence base exists for INNA screening, and the effectiveness estimates suggest that INNA screening can provide sensitivity for cervical epithelial abnormality that exceeds that of unassisted screening when INNA is used in either a substitutive or augmentative role.

ISSUES The colposcope was developed in 1925 and is well established in clinical gynecologic practice for defining and delineating cytologically detected lesions mainly of the cervix but also the vagina and vulva. Additionally, various endoscopic procedures in gastroenterology, pulmonary and urologic lesions enhance the cytologic detection and histologic verification of precancerous and cancerous lesions. The cost-effectiveness of all these devices and their applicability, particularly in countries with a limited health budget, is a major issue. This task force considered aspects of the present state of the art and the challenges in the 21st century. CONSENSUS POSITION Automated cytology can interface with colposcopic examination in a number of significant ways. Automated cytologic analysis of conventional cervical smears can potentially direct colposcopic examination by predicting the nature of a lesion, assist in determining which patients should receive colposcopy and, in some settings, thereby reduce the number of colposcopies. Potentially, various combinations of automated cytology and colposcopy may be used to generate screening protocols that might result in more effective and inexpensive screening. The role of cervicography, or high-resolution cervical photography, as a screening device remains to be defined. Sensitivity for high grade lesions is generally no greater than that in cytology, and specificity appears lower. The interpretation of cervical photographs in triage of mildly abnormal cytology may prove to be useful in countries with established cytology programs. In areas of the world where cytology screening programs are not in place, the interpretation of cervical photographs may have its most dramatic effect. Cost-effectiveness analyses are needed. There are, at present, insufficient data for the evaluation of speculoscopy, a procedure using chemiluminescent illumination of the cervix for visualization of acetowhite areas. Basic training in colposcopy should be integrated into the residency programs of obstetrics and gynecology. Criteria for the adequate training of colposcopists should be developed. Continuing education programs in colposcopy should be developed when they are not already in existence. The cost-effectiveness of integrating colposcopy as a primary screening technique should be evaluated. Following a high-grade squamous intraepithelial lesion (HSIL) cytology result, colposcopically directed punch biopsy should be taken with or without endocervical curettage. This generally should precede the loop electrosurgical excision procedure (LEEP); however, in certain circumstances direct LEEP may be indicated. LEEP under colposcopic vision is an efficient way to treat an HSIL lesion of the cervix because the histologic extent and margins can be determined, unlike with laser surgery or cryosurgery. It is also more cost-effective than cold knife conization because general anesthesia and an operating room are unnecessary. Following LEEP, the endocervical canal should be examined colposcopically for any evidence of involvement. Lesions in the endocervix can then be removed with a different-shaped loop. Further research into Raman spectroscopy as a diagnostic aid in cervical pathology is needed, as is the use of micrococolpohysteroscopy for in vivo cytologic analyses, especially of the endocervical canal and transformation zone. Hysteroscopy is the most direct method for the diagnosis and treatment of intrauterine diseases. Hysteroscopic endometrial biopsy is more accurate than conventional biopsy methods. Cervical invasion of endometrial cancer can be detected by hysteroscopy. The depth of invasion, however, is more accurately determined by magnetic resonance imaging or computed tomography. ONGOING ISSUES Many topics for ongoing research and/or implementation are mentioned under "Consensus Position," above. (ABSTRACT TRUNCATED)

OBJECTIVE: To compare cytologists' detection of abnormalities when using neural network-assisted (NNA) review, as employed by the PAPNET Testing System and to compare the effectiveness of this mode of review to that of unassisted, conventional rescreening of cervical smears initially diagnosed as negative. STUDY DESIGN: The study was undertaken as part of a multicenter clinical trial involving over 10,000 smears from 10 investigation sites (9 academic institutions and 1 private laboratory). Using a subset of negative control smears from three university laboratories, the false negative detection yields of NNA review (performed using the PAPNET System) and conventional microscopic rescreening (performed as part of routine quality control practice) were compared. The false negative detection yield was defined as the percentage of rescreened negatives reclassified as abnormal. RESULTS: The results demonstrate that using NNA review, the detection yield offalse negative smears, as a proportion of negative smears reexamined, is statistically significantly greater than that obtained using conventional quality control rescreening. The false negative yield generated using NNA analysis was 6.2% (142/2293) versus 0.6% (82/13761) for conventional rescreening. A statistically significant improvement in identification of abnormality is observed for NNA review as opposed to unassisted rescreening despite constraining the comparison in the following ways: (1) comparing the yields of rescreening of negative smears obtained from the same time intervals for both methods, (2) comparing the yields of rescreening of negative smears obtained from the years after the Clinical Laboratory Improvement Act (1990 and 1991) for both methods, and (3) disregarding the identification of atypical squamous cells of undetermined significance/ atypical glandular cells of undetermined significance cases and comparing only the identification ofsquamous intraepithelial lesions using the two methods. CONCLUSION: Using neural network-assisted review, cytologists uncovered a significantly higher proportion of previously undetected cervical abnormalities per smear reexamined than they did using unassisted, conventional rescreening.

ISSUES General definitions of quality assurance and quality control (QA/C) have existed in many forms for decades, and a new discipline guides their application to diverse industrial and recently medical processes without much fanfare. However, in the field of cervical cytology screening, the range of QA/C options has recently broadened and become controversial. With the advent of new systems of terminology, larger-scale laboratories and new technologies--plus strong governmental and legal pressures in some nations--the range of extremely difficult and sometimes expensive QA/C choices our community faces is greater than ever. CONSENSUS POSITION At our conference, the basic definitions of QA/C posed little difficulty. Presentation of the range of methods in use today and of those based on new technologies where use is proposed or has just begun also was achieved with little or no dispute. However, there was lack of consensus on exactly how QA/C methods are to be assessed. Indeed, there was little consistency in the use of different outcome measures with which we can judge success or failure of specific QA/C options. In addition, the tension between pressure to adopt sometimes uncertain or expensive method enhancements and pressure to maintain affordability and the widest possible access for populations that most need cervical cytology screening is greater than ever. ONGOING ISSUES More data are required that would enable assessment of QA/C options with the clearest possible understanding of cost/benefits and current or new assumptions of risk. Other task forces, such as medicolegal, cost/benefit and those devoted to new technologies, are our essential partners in meeting the challenges described above.

Issues Optical digital imaging and its related technologies have applications in cytopathology that encompass training and education, image analysis, diagnosis, report documentation and archiving, and telecommunications. Telecytology involves the use of telecommunications to transmit cytology images for the purposes of diagnosis, consultation or education. This working paper provides a mainly informational overview of optical digital imaging and summarizes current technologic resources and applications and some of the ethical and legal implications of the use of these new technologies in cytopathology. Consensus position Computer hardware standards for optical digital imagery will continue to be driven mainly by commercial interests and nonmedical imperatives, but professional organizations can play a valuable role in developing recommendations or standards for digital image sampling, documentation, archiving, authenticity safeguards and teleconsultation protocols; in addressing patient confidentiality and ethical, legal and informed consent issues; and in providing support for quality assurance and standardization of digital image-based testing. There is some evidence that high levels of accuracy for telepathology diagnosis can be achieved using existing dynamic systems, which may also be applicable to telecytology consultation. Static systems for both telepathology and telecytology, which have the advantage of considerably lower cost, appear to have lower levels of accuracy. Laboratories that maintain digital image databases should adopt practices and protocols that ensure patient confidentiality. Individuals participating in telecommunication of digital images for diagnosis should be properly qualified, meet licensing requirements and use procedures that protect patient confidentiality. Such individuals should be cognizant of the limitations of the technology and employ quality assurance practices that ensure the validity and accuracy of each consultation. Even in an informal teleconsultation setting one should define the extent of participation and be mindful of potential malpractice liability. Ongoing issues Digital imagery applications will continue to present new opportunities and challenges. Position papers such as this are directed toward assisting the profession to stay informed and in control of these applications in the laboratory. Telecytology is an area in particular need of studies of good quality to provide data on factors affecting accuracy. New technologic approaches to addressing the issue of selective sampling in static image consultation are needed. The use of artificial intelligence software as an adjunct to enhance the accuracy and reproducibility of cytologic diagnosis of digital images in routine and consultation settings deserves to be pursued. Other telecytology-related issues that require clarification and the adoption of workable guidelines include interstate licensure and protocols to define malpractice liability.

Issues The extension of automation to the diagnostic assessment of clinical materials raises issues of professional responsibility, on the part of both the medical professional and designer of the device. The International Academy of Cytology (IAC) and other professional cytology societies should develop a policy towards automation in the diagnostic assessment of clinical cytologic materials. Consensus position The following summarizes the discussion of the initial position statement at the International Expert Conference on Diagnostic Cytology Towards the 21st Century, Hawaii, June 1997. 1. The professional in charge of a clinical cytopathology laboratory continues to bear the ultimate medical responsibility for diagnostic decisions made at the facility, whether automated devices are involved or not. 2. The introduction of automated procedures into clinical cytology should under no circumstances lead to a lowering of standards of performance. A prime objective of any guidelines should be to ensure that an automated procedure, in principle, does not expose any patient to new risks, nor should it increase already-existing, inherent risks. 3. Automated devices should provide capabilities for the medical professional to conduct periodic tests of the appropriate performance of the device. 4. Supervisory personnel should continue visual quality control screening of a certain percentage of slides dismissed at primary screening as within normal limits (WNL), even when automated procedures are employed in the laboratory. 5. Specifications for the design of primary screening devices for the detection of cervical cancer issued by the IAC in 1984 were reaffirmed. 6. The setting of numeric performance criteria is the proper charge of regulatory agencies, which also have the power of enforcement. 7. Human expert verification of results represents the "gold standard" at this time. Performance characteristics of computerized cytology devices should be determined by adherence to defined and well-considered protocols. Manufacturers should not claim a new standard of care; this is the responsibility of the medical community and professional groups. 8. Cytology professionals should support the development of procedures that bring about an improvement in diagnostic decision making. Advances in technology should be adopted if they can help solve problems in clinical cytology. The introduction of automated procedures into diagnostic decision making should take place strictly under the supervision and with the active participation and critical evaluation by the professional cytology community. Ongoing issues Guidelines should be developed for the communication of technical information about the performance of automated screening devices by the IAC to governmental agencies and national societies. Also, guidelines are necessary for the official communication of IAC concerns to industry, medicolegal entities and the media. Procedures and guidelines for the evaluation of studies pertaining to the performance of automated devices, performance metrics and definitions for evaluation criteria should be established.

OBJECTIVE: To evaluate the effectiveness of the PAP-NET Testing System in improving cervical smear screening accuracy as measured during routine screening. STUDY DESIGN: A review of several recently published studies on the effectiveness of PAPNET testing in clinical use. System performance was retrospectively and prospectively evaluated and compared to the conventional method of testing. The use of PAPNET rescreening to identify smears having more significant abnormalities than had been initially diagnosed was investigated. RESULTS: New studies demonstrate that PAPNET testing increases the detection of significant lesions and improves cytotechnologist performance in routine clinical practice. Less variable diagnostic results are achieved with PAPNET testing as compared to conventional methods. The system is effective in identifying atypical smears having more serious abnormalities. CONCLUSION: When used as a supplemental method in routine practice, as studies have shown, PAPNET testing can reduce interobserver variability and increase the detection of abnormality.

The fact that some cervical smears result in false-negative findings is an unavoidable and unpredictable consequence of the conventional (manual microscopic) method of screening. Errors in the detection and interpretation of abnormality are cited as leading causes of false-negative cytology findings; these are random errors that are not known to correlate with any patient risk factor, which makes the false-negative findings a “silent” threat that is difficult to prevent. Described by many as a labor-intensive procedure, the microscopic evaluation of a cervical smear involves a detailed search among hundreds of thousands of cells on each smear for a possible few that may indicate abnormality. Investigations into causes of false-negative findings preceding the discovery of high-grade lesions found that many smears had very few diagnostic cells that were often very small in size. These small cells were initially overlooked or misinterpreted and repeatedly missed on rescreening. PAPNET testing is designed to supplement conventional screening by detecting abnormal cells that initially may have been missed by microscopic examination. This interactive system uses neural networks, a type of artificial intelligence well suited for pattern recognition, to automate the arduous search for abnormality. The instrument focuses the review of suspicious cells by a trained cytologist. Clinical studies indicate that PAPNET testing is sensitive to abnormality typically missed by conventional screening and that its use as a supplemental test improves the accuracy of screening. (Am J Obstet Gynecol 1996;175:1114-9.)

Objective: To determine the sensitivity of cervical cancer smear screening with neural network-assisted ("NNA") rescreening.Methods: The Papnet system of NNA analysis of cervical smears has been in clinical use worldwide for over 3 years and has been the subject of over 22 published manuscripts reporting on data from over 202,000 smears. This investigation reviewed the results of these studies and classified each study according to study design using a systematic protocol based on reference validation, diagnostic threshold for abnormal, and outcome metric. This classification taxonomy allowed for weighted (based on number of cases in each study) pooling of studies for each study design class. The pooled effectiveness metrics were used to derive the sensitivity of cervical cancer screening with NNA rescreening, using a baseline unassisted screening sensitivity of 85%. Other effectiveness metrics determined by this analysis include NNA's sensitivity as a primary screener, comparisons with primary unassisted screening, and comparisons of NNA rescreening and unassisted rescreening.Results: Analyses of the weighted, pooled mean estimates for each of the principal outcome metrics indicate the sensitivity of cervical cancer screening with NNA ranges from 90% to 99%; most pooled estimates fall in the range of 97-99%. An economic analysis using the APL-based "Cervical Cancer Screen" computer model developed by Eddy (Eddy DM. Screening for cervical cancer. Ann Intern Med 1990;113:214-26) and these effectiveness estimates as inputs showed that NNA analysis involves an accepted level of resource expenditure (approximately $40,000 per life year saved) when added to unassisted screening on a triennial basis.Conclusion: The sensitivity of cervical cancer screening with NNA rescreening using the Papnet system yields sensitivities in excess of 90% and approaching 99%.

A practical and effective system for the computer-assisted screening of conventionally prepared cervical smears is presented and described. Recent developments in neural network technology have made computerized analysis of the complex cellular scenes found on Pap smears possible. The PAPNET® Cytological Screening System uses neural networks to automatically analyze conventional smears by locating and recognizing potentially abnormal cells. It then displays images of these objects for review and final diagnosis by qualified cytologists. The results of the studies presented indicate that the PAPNET system could be a useful tool for both the screening and rescreening of cervical smears. In addition, the system has been shown to be sensitive to some types of abnormalities which have gone undetected during manual screening.