Glossary


Abnormal interpretation rate

—a measure of the number of women whose mammogram interpretation leads to additional imaging or biopsy. See also Recall rate.

Accreditation

—in terms of mammography, the recognition of a facility that has been reviewed and meets specific measures of quality set forth by the Mammography Quality Standards Act (MQSA).

Adverse event

—an undesirable experience associated with mammography activities within the scope of MQSA, as defined by MQSA regulations.

Area under the receiver operating curve (AUC)

—can be interpreted for mammography as a measure of the ability of a diagnostician to discriminate a mammogram showing breast cancer from one not showing breast cancer when two such mammograms have been randomly selected and presented together.

Asymptomatic

—having no signs or symptoms of disease.

Automatic exposure control (AEC)

—a device that automatically controls one or more technique factors in order to obtain a desired quantity of radiation at a pre-selected location; such a device automatically terminates the exposure when the selected quantity of radiation has been delivered.

Axillary lymph node

—a lymph node in the armpit region that drains lymph channels from the breast. Axillary lymph node dissections are performed on women to determine if breast cancer cells have spread from the breast; the presence or absence of positive axillary lymph nodes is one of the most important predictors of patient outcome.


Benchmarks

—standard points of reference for performance measurements by which interpretive performance can be evaluated or compared.

Benign

—a non-cancerous growth or tumor; benign tumors do not spread to tissues around them or to other parts of the body.

BRCA1

—a gene located on the short arm of chromosome 17; when this gene is mutated, a woman is at greater risk of developing breast or ovarian cancer, or both, than women who do not have the mutation.

BRCA2

—a gene located on chromosome 13; a germ-line mutation (an inherited mutation found in all cells in the body) in this gene is associated with increased risk of breast cancer.

Breast biopsy

—refers to a procedure that involves obtaining a breast tissue specimen for microscopic analysis to establish a diagnosis; can be done surgically or with needles.

Breast Imaging Reporting and Data System (BI-RADS)

—a method used by radiologists to interpret and report in a standardized manner the results of mammography, ultrasound, and MRI used in breast cancer screening and diagnosis. There are currently seven BI-RADS assessment categories: Category 0, Need Additional Imaging Evaluation and/or Prior Mammograms for Comparison; Category 1, Negative; Cate-



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Improving Breast Imaging Quality Standards Glossary Abnormal interpretation rate —a measure of the number of women whose mammogram interpretation leads to additional imaging or biopsy. See also Recall rate. Accreditation —in terms of mammography, the recognition of a facility that has been reviewed and meets specific measures of quality set forth by the Mammography Quality Standards Act (MQSA). Adverse event —an undesirable experience associated with mammography activities within the scope of MQSA, as defined by MQSA regulations. Area under the receiver operating curve (AUC) —can be interpreted for mammography as a measure of the ability of a diagnostician to discriminate a mammogram showing breast cancer from one not showing breast cancer when two such mammograms have been randomly selected and presented together. Asymptomatic —having no signs or symptoms of disease. Automatic exposure control (AEC) —a device that automatically controls one or more technique factors in order to obtain a desired quantity of radiation at a pre-selected location; such a device automatically terminates the exposure when the selected quantity of radiation has been delivered. Axillary lymph node —a lymph node in the armpit region that drains lymph channels from the breast. Axillary lymph node dissections are performed on women to determine if breast cancer cells have spread from the breast; the presence or absence of positive axillary lymph nodes is one of the most important predictors of patient outcome. Benchmarks —standard points of reference for performance measurements by which interpretive performance can be evaluated or compared. Benign —a non-cancerous growth or tumor; benign tumors do not spread to tissues around them or to other parts of the body. BRCA1 —a gene located on the short arm of chromosome 17; when this gene is mutated, a woman is at greater risk of developing breast or ovarian cancer, or both, than women who do not have the mutation. BRCA2 —a gene located on chromosome 13; a germ-line mutation (an inherited mutation found in all cells in the body) in this gene is associated with increased risk of breast cancer. Breast biopsy —refers to a procedure that involves obtaining a breast tissue specimen for microscopic analysis to establish a diagnosis; can be done surgically or with needles. Breast Imaging Reporting and Data System (BI-RADS) —a method used by radiologists to interpret and report in a standardized manner the results of mammography, ultrasound, and MRI used in breast cancer screening and diagnosis. There are currently seven BI-RADS assessment categories: Category 0, Need Additional Imaging Evaluation and/or Prior Mammograms for Comparison; Category 1, Negative; Cate-

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Improving Breast Imaging Quality Standards gory 2, Benign Finding(s); Category 3, Probably Benign Finding—Short Interval Follow-Up Suggested; Category 4, Suspicious Abnormality—Biopsy Should Be Considered; Category 5, Highly Suggestive of Malignancy—Appropriate Action Should Be Taken; and Category 6, Known Biopsy—Proven Malignancy—Appropriate Action Should be Taken. Breast imaging specialist —specializes in interpreting the results of mammographic and non-mammographic imaging examinations of the breast, and performs interventional procedures including image-guided biopsies of the breast. Breast MRI —a magnetic resonance image taken of the breast. See also Magnetic resonance imaging. Breast ultrasound —an ultrasound image of the breast. See also Ultrasound. Cancer —a general term for more than 100 diseases in which abnormal cells divide without control. Cancer cells can invade nearby tissues and can spread through the bloodstream and lymphatic system to other parts of the body. There are several main types of cancer. Carcinoma is cancer that begins in the skin or in tissues that line or cover internal organs. Sarcoma is cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Leukemia is cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the bloodstream. Lymphoma is cancer that begins in the cells of the immune system. Cancer detection rate —the number of women identified as having breast cancer per 1,000 women examined. Cancer outcome —as defined in this report, the presence or absence of cancer as determined by the results of a biopsy. Cancer staging —performed after a cancer is diagnosed and generally derived from pathology reports; used in conjunction with other tumor prognostic indicators (such as tumor grade, hormone receptor status, and other factors) to determine the patient’s prognosis and treatment options. Cancer status —as defined in this report, the presence or absence of cancer in a given individual. Centralized interpretation —expert interpretation at one central location of either films or digitized data collected at multiple remote locations. Certification —as defined by MQSA regulations, the process of approval of a facility by FDA or a certification agency to provide mammography services. Clinical image —as defined by MQSA regulations, a mammogram. See also Mammogram. Clinical trial —a formal study carried out according to a prospectively defined protocol that is intended to discover or verify the safety and effectiveness of procedures or interventions in humans. The term may refer to a controlled or uncontrolled trial. Randomized controlled clinical trials are considered the gold standard for clinical evidence. Cohort study —an observational study in which outcomes in a group of patients that received an intervention are compared with outcomes in a similar group, that is, the cohort, either contemporary or historical, of patients that did not receive the intervention. In an adjusted- (or matched-) cohort study, investigators identify (or make

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Improving Breast Imaging Quality Standards statistical adjustments to provide) a cohort group that has characteristics (e.g., age, gender, disease severity) that are as similar as possible to the group that experienced the intervention. Collimator —a device on the mammography unit used to control the size and shape of the x-ray beam. Compression paddle —a component of the mammography unit used to compress the breast in order to spread the breast tissue evenly for the x-ray; the correct amount of compression allows for the highest quality image with the lowest possible radiation dose. Compression paddles are regulated under MQSA. Computed tomography (CT) —a special radiographic modality that uses a computer to assimilate multiple x-ray images into a two-dimensional, cross-sectional image, which also can be reconstructed into a three-dimensional image. This can reveal many soft tissue structures not shown by conventional radiography. Computer-aided detection (CAD) —use of sophisticated computer programs designed to recognize patterns in images and provide assistance to interpreters to detect the presence of disease. This approach has been used along with mammography for the detection of breast cancer. Confidence interval —a range within which an estimate is deemed to be close to the actual value being measured. In statistical measurements, estimates cannot be said to be exact matches, but rather, are defined in terms of their probability of matching the value of the characteristic being measured. Confounding factors —factors for which data adjustment is needed because they are entangled with other factors related to the disease or condition of interest. Consensus double reading —see Double reading. Conspicuity —the ability of a lesion or abnormality to be seen over the background “noise” of a mammogram; conspicuity=lesion contrast/background complexity. Context bias —as defined in mammography, when an individual is more likely to consider a mammogram abnormal when it is reviewed in a specially assembled sample with high disease prevalence than when the same film is interpreted as part of a group with lower disease prevalence. Core-needle biopsy —procedure in which a hollow needle is used to remove small cylinders of tissue from a suspected tumor. Cost-benefit analysis —a comparison of alternative interventions in which costs and outcomes are quantified in common monetary units. Cumulative risk —a quantitative measure of the probability of an occurrence over a specific time period. Cytological screening —examination of cells for changes indicative of a disease or risk of disease, for example, Papanicolaou test (Pap smear) for cervical cancer. Cytology —the study of cells using a microscope to examine the characteristics of formation, structure, and function of cells. Darkroom fog —added optical density on a film due to light leaks or safe lights in a darkroom; degrades image contrast and must be tested and eliminated to ensure image quality. Detection —identifying disease. Early detection means that the disease is found at an early stage, before it has grown large or spread to other sites.

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Improving Breast Imaging Quality Standards Diagnosis —definitive confirmation of a specific disease usually by imaging procedures and from the use of laboratory findings. Diagnostic mammography —x-ray-based breast imaging undertaken for the purpose of diagnosing an abnormality discovered by physical exam or screening mammography. Women who have physical symptoms, a personal history of breast cancer, or breast implants also often undergo diagnostic mammograms. Digital mammography —see Full field digital mammography. Dosimetry —measurement or calculation of radiation dose. Radiation dose is the energy absorbed per unit mass of tissue. Double reading —a process by which a mammogram is reviewed twice for any potential abnormalities. Independent double reading is when both readers interpret the mammography films without knowledge of the other’s assessment and the most abnormal reading is acted upon. Consensus double reading is when both readers learn the other’s interpretation result and resolve the differences together (arbitration). Duct —a hollow passage for gland secretions. In the breast, a passage through which milk passes from the lobule (which makes the milk) to the nipple. Ductal carcinoma in situ —a lesion in which there is proliferation of abnormal cells within the ducts of the breast, but no visible evidence of invasion into the duct walls or surrounding tissues; sometimes referred to as “precancer” or “preinvasive cancer.” Established operating level —the value of a particular quality assurance parameter that has been established as an acceptable normal level by a mammography facility’s quality assurance program. Exposure reproducibility coefficient of variation evaluation —a test performed to ensure radiation exposure levels from a radiographic unit are reproducible within a certain range; ensures consistency in the amount of radiation emitted from a radiographic device. Facility —as defined in this report, a hospital, outpatient department, clinic, radiology practice, mobile unit, office of a physician, or other facility that conducts mammography activities, including the following: operation of equipment to produce a mammogram, processing of the mammogram, initial interpretation of the mammogram, and maintaining viewing conditions for the interpretation. False-negative result —a test result that incorrectly indicates that the abnormality or disease being investigated is not present when in fact it is present. False-positive rate —the number of false-positive results per 100 women screened. False-positive result —a test result that indicates that the abnormality or disease being investigated is present when in fact it is not. There are three levels of false-positive measurement in mammography: FP1, no known cancer within one year of a BI-RADS Category 0, 4, or 5 assessment (of a screening mammogram); FP2, no known cancer within one year of a BI-RADS Category 4 or 5 assessment (usually from a diagnostic mammogram); and FP3, no known cancer within one year of a BI-RADS Category 4 or 5 assessment, for which biopsy was actually performed. Federal Certificates of Confidentiality —a certificate issued by the federal government that protects those with access to research data from being compelled to identify re-

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Improving Breast Imaging Quality Standards search subjects in any “Federal, State, or local civil, criminal, administrative, legislative, or other proceedings,” with limited exceptions. Film processor —a machine for developing and treating photographic films (e.g., x-ray films) to produce permanent visible images. Fine-needle aspiration —a procedure by which a thin needle is used to draw up (aspirate) samples for examination under a microscope. Full field digital mammography (FFDM) —similar to conventional mammography (film-screen mammography) except that a dedicated electronic detector system is used to computerize and display the x-ray information. Full-time equivalent —as defined in this report, a person employed full-time (37.5+ hours per week of paid employment for 40 or more weeks per year) and spends at least 80 percent of his or her time performing clinical radiology imaging interpretation or related imaging tasks. Half value layer —the thickness of an absorbing substance necessary to reduce by one half the initial intensity of the radiation passing through it. Health maintenance organization (HMO) —organized system for providing comprehensive prepaid health care that has five basic attributes: (1) provides care in a defined geographic area; (2) provides or ensures delivery of an agreed-upon set of basic and supplemental health maintenance and treatment services; (3) provides care to a voluntarily enrolled group of persons; (4) requires their enrollees to use the services of designated providers; and (5) receives reimbursement through a predetermined, fixed, periodic prepayment made by the enrollee without regard to the degree of services provided. Illumination —the total luminous flux (the amount of energy emitted by a light source in all directions) incident per unit area; refers to the amount of incident light. In situ —in position, localized. In breast tissue, it usually refers to either ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS). Incidence —the number of new cases of a disease that occur in the population per unit of time. Incident screen —screening tests performed at regular intervals after an initial (prevalent) screen for a particular disease. Indemnity payments —compensation for damage, loss, or injury suffered. Independent double reading —see Double reading. Interobserver variability —variability between observers. Interpreting physician —a licensed physician who meets MQSA requirements for interpreting mammograms. Interpretive volume —the number of mammograms an interpreting physician reads over a given period of time. Currently, MQSA requires interpreting physicians to read at least 960 mammograms over a given 2-year period. Interval cancer —a cancer detected between regular screening examinations. See also Screening interval. Interventional mammographic procedures —minimally invasive procedures that are done under the guidance of mammography images, such as needle biopsies and presurgery wire localization of a tumor.

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Improving Breast Imaging Quality Standards Intraobserver variability —variability by the same observer. Invasive cancer —cancers capable of growing beyond their site of origin and invading neighboring tissue. Invasive ductal carcinoma —a cancer that starts in the ducts of the breast and then breaks through the duct wall, where it invades the surrounding tissue; it is the most common type of breast cancer and accounts for about 80 percent of breast malignancies. Invasive lobular carcinoma —a cancer that starts in the milk-producing glands (lobules) of the breast and then breaks through the lobule walls to involve the surrounding tissue; accounts for about 15 percent of invasive breast cancers. Ionizing radiation —a form of electromagnetic radiation capable of removing electrons from atoms in a substance, such as cellular material; examples include x-rays, which can be used in medical diagnosis and treatment. Kilovolt peak (kVp) —a measure of the maximum energy of an x-ray produced across an x-ray tube; standards for accuracy and reproducibility of the clinical kVp for mammography are established under MQSA. Latent distribution —distribution of a continuous variable that cannot be measured directly, but is hypothesized to underlie an observed categorical variable. Lesion —an abnormal change in the structure of an organ or other body part due to injury or disease; especially one that is circumscribed and well defined. Lobular carcinoma in situ —abnormal cells within a breast lobule that have not invaded surrounding tissue. Not cancer per se, but can serve as a marker of future cancer risk. Lobular —of or pertaining to the lobes of an organ, such as the liver, lung, breast, thyroid, or brain. Luminance —the amount of light “reflected” from a surface. Magnetic resonance imaging (MRI) —method by which images are created by recording signals generated from the excitation (the gain and loss of energy) of elements such as the hydrogen of water in tissue when placed within a powerful magnetic field and pulsed with radio frequencies. Malignant —a tumor that has the potential to become lethal through destructive growth or by having the ability to invade surrounding tissue and metastasize. Mammogram —x-ray image of the breast. Mammography —the practice of imaging breast tissue with x-rays for screening or diagnostic purposes in detecting or diagnosing cancer. Mammography Quality Standards Act (MQSA) —enacted by Congress (initially in 1992 and reauthorized in 1998 and 2004) to ensure that all women have access to quality mammography for the detection of breast cancer in its earliest, most treatable stages. MQSA regulations, promulgated by FDA 1993 and updated in 1999, established national quality standards for mammography equipment and personnel. Medicaid —federal- and state-funded health insurance program for certain low-income people. It covers approximately 36 million individuals including children; aged, blind, and/or disabled people; and people who are eligible to receive federally assisted income maintenance payments.

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Improving Breast Imaging Quality Standards Medical audit —a formal examination of the quality of practice in a particular area of medicine; often involves benchmarking against best practice. Medical physicist —an individual who is competent to practice, independently, one or more of the sub-fields of medical physics, including therapeutic radiological physics, diagnostic radiological physics, medical health physics, or medical nuclear physics. In this report, a person trained in evaluating the performance of mammography equipment and facility quality assurance programs, and who meets MQSA requirements. Medicare —a program that provides health insurance to people age 65 and over, those who have permanent kidney failure, and people with certain disabilities. Meta-analysis —systematic methods that use statistical techniques for combining results from different studies to obtain a quantitative estimate of the overall effect of a particular intervention or variable on a defined outcome. This combination may produce a stronger conclusion than can be provided by any individual study (also known as data synthesis or quantitative overview). Microcalcifications —tiny calcium deposits within the breast, singly or in clusters; often found by mammography. They may be a sign of cancer. Mobile mammography —a mammography x-ray unit located in a vehicle (truck, van, etc.) that is driven from one location to another to perform mammography. Typically, services are provided in one of two types of vehicles, either a recreational vehicle that has been customized to fit a mammography unit, processor, and exam rooms (mobile van), or a standard passenger van that has been customized to allow for the transportation of a mammography unit to various indoor locations (portable unit). Modality —a method of application or use of any therapy or medical device. A mammographic modality is a technology for radiography of the breast, for example screen-film mammography. Mode of interpretation (online vs. batch) —methods by which screening mammograms can be interpreted; online interpretation is when an interpreting physician reads the mammogram while the patient is still at the facility; batch interpretation is when screening mammograms are grouped by facility personnel for later interpretation by an interpreting physician during a focused, uninterrupted period of time. Morbidity —a diseased condition or state; the incidence of a disease or of all diseases in a population. Mortality rate —the death rate; expresses the number of deaths in a unit of population within a prescribed time and may be expressed as crude death rates or as death rates specific for diseases and, sometimes, for age, sex, or other attributes. Negative predictive value (NPV) —the proportion of all women with a negative result who are actually free of the disease. Calculated as the number of true-negative results divided by the number of true-negative results plus the number of false-negative results; formula (NPV=TN/[TN+FN]). Node positivity —the presence of cancer cells in lymph nodes near the primary cancer site. Non-invasive ductal carcinoma in situ (DCIS) —see Ductal carcinoma in situ. Nonpalpable abnormality —breast abnormalities that can be seen on a mammogram but cannot be felt.

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Improving Breast Imaging Quality Standards Normal distribution —a family of probability distributions of the same general form, differing in their location (mean) and scale (standard deviation) parameters; also known as a Gaussian distribution or bell curve. Occult tumor —a tumor that is undetected and without symptoms. Oncology —the branch of medicine dealing with tumors. Optical density —a measure of light transmitted through film. The higher the optical density, the darker the film. Scientifically it is defined as the base ten logarithm of the ratio of the incident intensity of light to the transmitted intensity. Mean optical density, monitored under MQSA, is the average of the optical densities measured on the images produced with a given equipment configuration during the AEC performance test using 2, 4, and 6 centimeter thicknesses of a homogeneous material. Ordinal-level data —categorical data that can be grouped or ranked; however, differences in data values either cannot be determined or are meaningless. Palpable tumor —a tumor that can be felt during a physical examination. Papanicolaou (Pap) smear —a cytological test developed by George N.Papanicolaou for the detection of cervical cancer. Pathology —examination of a tissue sample (from a biopsy or surgical resection) to determine whether a lesion is benign or malignant, to differentiate between different types of cancer, and to reveal the extent of the cancer’s spread. Phantom image —a radiographic image of a test object (a phantom) used to simulate radiographic characteristics of compressed breast tissue and containing components that radiographically model aspects of breast disease and cancer. Positive mammogram —a mammogram that has an overall assessment of findings that are either “suspicious” or “highly suggestive of malignancy.” Positive predictive value (PPV) —a measure of accuracy for a screening or diagnostic test; indicates what portion of those with an abnormal test result actually have the disease. Calculated as the number of true-positive results divided by the number of true-positive results plus the number of false-positive results; formula (PPV=TP/[TP+ FP]). Positron emission tomography (PET) —use of radioactive tracers such as labeled glucose to identify regions in the body with altered metabolic activity. PPV1 —the proportion of all women with positive examinations (BI-RADS Category 0, 4, or 5) who are diagnosed with breast cancer; formula (PPV1=TP/[TP+FP1]). PPV2 —the proportion of all women recommended for biopsy after mammography (BI-RADS Category 4 or 5) who are diagnosed with breast cancer; formula (PPV2=TP/[TP+FP2]). PPV3 —the proportion of all women biopsied due to the interpreting physician’s recommendation who are diagnosed with cancer at the time of biopsy; formula (PPV3=TP/[TP+FP3]). Preoperative mammographic needle localization —see Core-needle biopsy and Stereotactic breast biopsy. Prevalence —the number of cases of disease, infected persons, or persons with some other attribute, present at a particular time and in relation to the size of the population from which they are drawn.

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Improving Breast Imaging Quality Standards Prevalent screen —initial screening test for a particular disease. Progression —the growth or advancement of cancer, indicating a worsening of the disease. Radiation dose —a generic term to describe the amount of radiation a person receives, either naturally or through medical procedures, for example x-ray imaging. Radiologic technologist —an individual specifically trained in the use of radiographic equipment and the positioning of patients for radiographic examinations and, in this report, who meets MQSA requirements. Radiologist assistant —an advanced-level radiologic technologist who works under the supervision of a radiologist. Radiology information systems —computerized management systems developed to assist radiology facilities in collecting and organizing patient information; services include patient registration and scheduling, dictation and transcription, multisite support, data access, and image routing and archive management. Recall rate —the proportion of all women undergoing screening mammography who are given a positive interpretation that requires additional examinations. See also Abnormal interpretation rate. Receiver operating curve (ROC) analysis —a statistical methodology used to quantify the ability to correctly distinguish signals of interest from background noise in the system. ROC analysis can be used in mammography to demonstrate the relationship between the true-positive (sensitivity) and false-positive rates (specificity). Resource-based relative value scale (RBRVS) —a method of comparing the relative work for a physician providing a particular service to the work involved with providing other services; the Centers for Medicare and Medicaid Services use this system to reimburse physicians for services provided to Medicare recipients. Review physician —a physician qualified under MQSA regulations to review clinical images on behalf of an accreditation body. Risk —a quantitative measure of the probability of developing or dying from a particular disease such as cancer. Scintimammography —use of radioactive tracers to produce an image of the breast. Screen-film (analog) mammography —conventional mammography in which the x-rays are recorded on film. Screen-film contact —the contact between the intensifying screen and the x-ray film when performing mammography, which has a significant influence on image sharpness. Mammography cassettes are to be replaced when radiographs of a special screen-film test tool reveal persistent large areas of increased optical density. Screening —systematic testing of an asymptomatic population to determine the presence of a particular disease. Screening interval —the frequency with which a screening test is carried out. Recommended screening intervals vary for mammography; the American Cancer Society recommends annual screening for women over the age of 40, the U.S. Preventative Services Task Force recommends screening every 1 to 2 years for the same age group, and the American College of Obstetricians and Gynecologists suggest screen-

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Improving Breast Imaging Quality Standards ing every 1 to 2 years for women aged 40–49 and annually for women aged 50 and older. Screening mammography —x-ray-based breast imaging in an asymptomatic population used to detect breast cancers at an early stage. SEER registries —the Surveillance, Epidemiology, and End Results (SEER) Program currently collects and publishes cancer incidence and survival data from 14 population-based cancer registries and three supplemental registries covering approximately 26 percent of the U.S. population. The SEER registries routinely collect data on patient demographics, primary tumor site, morphology, stage at diagnosis, first course of treatment, and follow-up for vital status. Sensitivity —a measure of how often a test correctly identifies women with breast cancer. Calculated as the number of true-positive results divided by the number of true-positive results plus the number of false-negative results; formula (Se=TP/[TP+FN]). Short interval follow-up examination —typically assigned in BI-RADS Category 3 cases, when a finding has a high probability of being benign, is not expected to change over the follow-up interval (typically 6 months), and the interpreting physician wishes to ascertain its stability. Soft copy —image display on a computer screen rather than on film. Sonography —a technique in which high-frequency sound waves are bounced off internal organs and the echo pattern is converted into a two-dimensional picture of the structures beneath the transducer. See also Ultrasound. Specificity —the proportion of persons without disease who correctly test negative. Calculated as the number of true-negative results divided by the number of true-negative results plus the number of false-positive results; formula (Sp=TN/[TN+FP]). Stereotactic breast biopsy —use of breast images (x-rays) taken at various angles to generate a three-dimensional image for plotting the exact position of a suspicious lesion and for guiding the placement of a biopsy needle. System artifacts —abnormalities that result from problems with any part the of mammography system including the x-ray unit and the processing of mammographic films, potentially complicating accurate interpretation; causes include use of abrasive materials to clean processor rollers, an improperly installed or vented processor, inadequate chemical quality, and variations in developer temperature. Tail coverage —malpractice insurance that can be purchased after the expiration of a claims-made liability policy to cover claims made during an extended reporting or discovery period. Such insurance covers radiologists who retire (or move) who are later sued for missed diagnoses made at facilities at which they were formerly employed. Telemammography —the process of satellite or long-distance transmission of digital mammography for consultation. Three phase x-ray generator —a machine that transforms the commercial electric power current (or line voltage, usually produced and delivered as a three phase alternating current) into a high-voltage direct current for x-ray production. True-negative rate —see Specificity. True-positive rate —see Sensitivity.

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Improving Breast Imaging Quality Standards Tumor registry —a population-based resource for examining cancer patterns. Tumor size —the physical dimensions of a tumor, which may be determined based on palpation, imaging, or pathology; an important element of tumor staging. Tumor staging —the grouping of cancer cases into broad categories based on extent of disease using a coded format, such as a numerical system with increasing values meaning more involvement or severity. Extent of disease is a detailed description of how far the tumor has spread from the site of origin (the primary site). Ultrasound —use of inaudible, high-frequency sound waves to create an image of the body. Verification bias —the potential for overestimation of sensitivity and underestimation of specificity when a gold standard assessment of disease status may only be partially available. Wire needle localization —a procedure used to guide a surgical breast biopsy when the breast lump is difficult to locate or in areas that look suspicious on the mammogram but do not have a distinct lump (nonpalpable abnormalities); mammogram images are used to guide the needle to the suspicious area of the breast. X-ray —a type of ionizing radiation used for imaging purposes that uses energy beams of very short wavelengths (0.1 to 100 Angstroms) that can penetrate most substances except heavy metals.

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