Computer-aided diagnosis
Encyclopedia
Computer-aided detection (CADe) and computer-aided diagnosis (CADx) are procedures in medicine that assist doctors in the interpretation of medical images. Imaging techniques in X-ray
, MRI, and Ultrasound
diagnostics yield a great deal of information, which the radiologist has to analyze and evaluate comprehensively in a short time. CAD systems help scan digital images, e.g. from computed tomography, for typical appearances and to highlight conspicuous sections, such as possible diseases.
CAD is a relatively young interdisciplinary technology combining elements of artificial intelligence
and digital image processing with radiological
image processing. A typical application is the detection of a tumor. For instance, some hospitals use CAD to support preventive medical check-ups in mammography
(diagnosis of breast cancer), the detection of polyps in the colon, and lung cancer
.
. X-ray images are scanned for suspicious structures. Normally a few thousand images are required to optimize the algorithm. Digital image data are copied to a CAD server in a DICOM-format and are prepared and analyzed in several steps.
1. Preprocessing for
2. Segmentation for
3. Structure/ROI (Region of Interest) Analyze
Every detected region is analyzed individually for special characteristics:
4. Evaluation / classification
After the structure is analyzed, every ROI is evaluated individually (scoring) for the probability of a TP. Therefore the procedures are:
If the detected structures have reached a certain threshold level, they are highlighted in the image for the radiologist. Depending on the CAD system these markings can be permanently or temporary saved. The latter’s advantage is that only the markings which are approved by the radiologist are saved. False hits should not be saved, because an examination at a later date becomes more difficult then.
A correct hit is termed a True Positive (TP), while the incorrect marking of healthy sections constitutes a False Positive (FP). The less FPs indicated, the higher the specificity is. A low specificity reduces the acceptance of the CAD system because the user has to identify all of these wrong hits. The FP-rate in lung overview examinations (CAD Chest) could be reduced to 2 per examination. In other segments (e.g. CT lung examinations) the FP-rate could be 25 or more.
, lung cancer
, colon cancer, prostate cancer
, bone metastases
, coronary artery disease and congenital heart defect
.
(X-ray examination of the female breast). Screening mammography is used for the early detection of breast cancer. CAD is especially established in US and the Netherlands and is used in addition to human evaluation, usually by a radiologist. The first CAD system for mammography was developed in a research project at the University of Chicago. Today it is commercially offered by iCAD and Hologic
. There are currently some non-commercial projects being developed, such as Ashita Project, a gradient-based screening software by Alan Hshieh, as well. However, while achieving high sensitivities, CAD systems tend to have very low specificity and the benefits of using CAD remain uncertain. Some studies suggest a positive impact on mammography screening programs, but others show no improvement. A 2008 systematic review on computer-aided detection in screening mammography concluded that CAD does not have a significant effect on cancer detection rate, but does undesirably increase recall rate (i.e. the rate of false positives). However, it noted considerable heterogeneity in the impact on recall rate across studies.
Procedures to evaluate mammography based on magnetic resonance imaging
exist too.
with special three-dimensional CAD systems are established and considered as gold standard. At this a volumetric dataset with up to 3,000 single images is prepared and analyzed. Round lesions (lung cancer
, metastases and benign changes) from 1 mm are detectable. Today all well-known vendors of medical systems offer corresponding solutions.
Early detection of lung cancer is valuable. The 5-year-survival-rate of lung cancer has stagnated in the last 30 years and is now at approximately just 15%. Lung cancer takes more victims than breast cancer, prostate cancer and colon cancer together. This is due to the asymptomatic growth of this cancer. In the majority of cases it is too late for a successful therapy if the patient develops first symptoms (e.g. chronic croakiness or hemoptysis). But if the lung cancer is detected early (mostly by chance), there is a survival rate at 47% according to the American Cancer Society.
At the same time the standard x-ray-examination of the lung is the most frequently x-ray examination with a 50% share. Indeed the random detection of lung cancer in the early stage (stage 1) in the x-ray image is difficult. It is a fact that round lesions vary from 5–10 mm are easily overlooked.
The routine application of CAD Chest Systems may help to detect small changes without initial suspicion. Philips
was the first vendor to present a CAD for early detection of round lung lesions on x-ray images.
s in the colon
. Polyps are small growths that arise from the inner lining of the colon. CAD detects the polyps by identifying their characteristic "bump-like" shape. To avoid excessive false positives, CAD ignores the normal colon wall, including the haustra
l folds. In early clinical trials, CAD helped radiologists find more polyps in the colon than they found prior to using CAD.
) coronary artery disease in coronary CT angiography (CCTA) studies. A low false positives rate (60-70% specificity per patient) allows using CAD as a screening device distinguishing between positive and negative studies and yielding a preliminary report. This, for example, can be used for chest pain patients' triage in an emergency setting.
with a digital stethoscope and specialized software, also known as Computer-aided auscultation
. Murmurs, irregular heart sounds, caused by blood flowing through a defective heart, can be detected with high sensitivity and specificity. Computer-aided auscultation
is sensitive to external noise and bodily sounds and requires an almost silent environment to function accurately.
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
, MRI, and Ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
diagnostics yield a great deal of information, which the radiologist has to analyze and evaluate comprehensively in a short time. CAD systems help scan digital images, e.g. from computed tomography, for typical appearances and to highlight conspicuous sections, such as possible diseases.
CAD is a relatively young interdisciplinary technology combining elements of artificial intelligence
Artificial intelligence
Artificial intelligence is the intelligence of machines and the branch of computer science that aims to create it. AI textbooks define the field as "the study and design of intelligent agents" where an intelligent agent is a system that perceives its environment and takes actions that maximize its...
and digital image processing with radiological
Radiology
Radiology is a medical specialty that employs the use of imaging to both diagnose and treat disease visualized within the human body. Radiologists use an array of imaging technologies to diagnose or treat diseases...
image processing. A typical application is the detection of a tumor. For instance, some hospitals use CAD to support preventive medical check-ups in mammography
Mammography
Mammography is the process of using low-energy-X-rays to examine the human breast and is used as a diagnostic and a screening tool....
(diagnosis of breast cancer), the detection of polyps in the colon, and lung cancer
Lung cancer
Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...
.
Overview
Computer-aided detection (CADe) systems are usually confined to marking conspicuous structures and sections. Computer-aided diagnosis (CADx) systems evaluate the conspicuous structures. For example, in mammography CAD highlights micro calcification clusters and hyperdense structures in the soft tissue. This allows the radiologist to draw conclusions about the condition of the pathology. Another application is CADq, which quantifies, e.g., the size of a tumor or the tumor’s behavior in contrast medium uptake. At the present stage of the technology, CAD cannot and may not substitute the doctor, but rather plays a supporting role. The doctor (generally a radiologist) is always responsible for the final interpretation of a medical image.Methodology
CAD is fundamentally based on highly complex pattern recognitionPattern recognition
In machine learning, pattern recognition is the assignment of some sort of output value to a given input value , according to some specific algorithm. An example of pattern recognition is classification, which attempts to assign each input value to one of a given set of classes...
. X-ray images are scanned for suspicious structures. Normally a few thousand images are required to optimize the algorithm. Digital image data are copied to a CAD server in a DICOM-format and are prepared and analyzed in several steps.
1. Preprocessing for
- Reduction of artifacts (bugs in images)
- Image noise reduction
- Leveling (harmonization) of image quality for clearing the image’s different basic conditions e.g. different exposure parameter.
2. Segmentation for
- Differentiation of different structures in the image, e.g. heart, lung, ribcage , possible round lesions
- Matching with anatomic databank
3. Structure/ROI (Region of Interest) Analyze
Every detected region is analyzed individually for special characteristics:
- Compactness
- Form, size and location
- Reference to close-by structures / ROIs
- Average greylevel value analyze within a ROI
- Proportion of greylevels to border of the structure inside the ROI
4. Evaluation / classification
After the structure is analyzed, every ROI is evaluated individually (scoring) for the probability of a TP. Therefore the procedures are:
- Nearest-Neighbor Rule
- Minimum distance classifier
- Cascade Classifier
- Bayesian Classifier
- Multilayer perception
- Radial basis function network (RBF)
- SVM
If the detected structures have reached a certain threshold level, they are highlighted in the image for the radiologist. Depending on the CAD system these markings can be permanently or temporary saved. The latter’s advantage is that only the markings which are approved by the radiologist are saved. False hits should not be saved, because an examination at a later date becomes more difficult then.
Sensitivity and specificity
CAD systems seek to highlight suspicious structures. Today's CAD systems cannot detect 100% of pathological changes. The hit rate (sensitivity) can be up to 90% depending on system and application.A correct hit is termed a True Positive (TP), while the incorrect marking of healthy sections constitutes a False Positive (FP). The less FPs indicated, the higher the specificity is. A low specificity reduces the acceptance of the CAD system because the user has to identify all of these wrong hits. The FP-rate in lung overview examinations (CAD Chest) could be reduced to 2 per examination. In other segments (e.g. CT lung examinations) the FP-rate could be 25 or more.
Absolute detection rate
The absolute detection rate of the radiologist is an alternative metric to sensitivity and specificity. Overall, results of clinical trials about sensitivity, specificity, and the absolute detection rate can vary markedly. Each study result depends on its basic conditions and has to be evaluated on those terms. The following facts have a strong influence:- Retrospective or prospective design
- Quality of the used images
- Condition of the x-ray examination
- Radiologist's experience and education
- Type of tumor
- Size of the considered tumor
Applications
CAD is used in the diagnosis of breast cancerBreast cancer
Breast cancer is cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas...
, lung cancer
Lung cancer
Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...
, colon cancer, prostate cancer
Prostate cancer
Prostate cancer is a form of cancer that develops in the prostate, a gland in the male reproductive system. Most prostate cancers are slow growing; however, there are cases of aggressive prostate cancers. The cancer cells may metastasize from the prostate to other parts of the body, particularly...
, bone metastases
Bone Metastases
Bone metastases, or metastatic bone disease, is a class of cancer metastases that results from primary tumor invasion to bone. Bone-originating cancers like osteosarcoma, chondrosarcoma, and Ewing's sarcoma are rare...
, coronary artery disease and congenital heart defect
Congenital heart defect
A congenital heart defect is a defect in the structure of the heart and great vessels which is present at birth. Many types of heart defects exist, most of which either obstruct blood flow in the heart or vessels near it, or cause blood to flow through the heart in an abnormal pattern. Other...
.
Breast cancer
CAD is used in screening mammographyMammography
Mammography is the process of using low-energy-X-rays to examine the human breast and is used as a diagnostic and a screening tool....
(X-ray examination of the female breast). Screening mammography is used for the early detection of breast cancer. CAD is especially established in US and the Netherlands and is used in addition to human evaluation, usually by a radiologist. The first CAD system for mammography was developed in a research project at the University of Chicago. Today it is commercially offered by iCAD and Hologic
Hologic
Hologic corporation is a developer, manufacturer and supplier of diagnostic and medical imaging systems related to women's health. It develops digital imaging technology for general radiography and mammography applications...
. There are currently some non-commercial projects being developed, such as Ashita Project, a gradient-based screening software by Alan Hshieh, as well. However, while achieving high sensitivities, CAD systems tend to have very low specificity and the benefits of using CAD remain uncertain. Some studies suggest a positive impact on mammography screening programs, but others show no improvement. A 2008 systematic review on computer-aided detection in screening mammography concluded that CAD does not have a significant effect on cancer detection rate, but does undesirably increase recall rate (i.e. the rate of false positives). However, it noted considerable heterogeneity in the impact on recall rate across studies.
Procedures to evaluate mammography based on magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
exist too.
Lung cancer (bronchial carcinoma)
In the diagnosis of lung cancer, computed tomographyComputed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
with special three-dimensional CAD systems are established and considered as gold standard. At this a volumetric dataset with up to 3,000 single images is prepared and analyzed. Round lesions (lung cancer
Lung cancer
Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...
, metastases and benign changes) from 1 mm are detectable. Today all well-known vendors of medical systems offer corresponding solutions.
Early detection of lung cancer is valuable. The 5-year-survival-rate of lung cancer has stagnated in the last 30 years and is now at approximately just 15%. Lung cancer takes more victims than breast cancer, prostate cancer and colon cancer together. This is due to the asymptomatic growth of this cancer. In the majority of cases it is too late for a successful therapy if the patient develops first symptoms (e.g. chronic croakiness or hemoptysis). But if the lung cancer is detected early (mostly by chance), there is a survival rate at 47% according to the American Cancer Society.
At the same time the standard x-ray-examination of the lung is the most frequently x-ray examination with a 50% share. Indeed the random detection of lung cancer in the early stage (stage 1) in the x-ray image is difficult. It is a fact that round lesions vary from 5–10 mm are easily overlooked.
The routine application of CAD Chest Systems may help to detect small changes without initial suspicion. Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
was the first vendor to present a CAD for early detection of round lung lesions on x-ray images.
Colon cancer
CAD is available for detection of colorectal polypColorectal polyp
A colorectal polyp is a polyp occurring on the lining of the colon or rectum. Untreated colorectal polyps can develop into colorectal cancer....
s in the colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
. Polyps are small growths that arise from the inner lining of the colon. CAD detects the polyps by identifying their characteristic "bump-like" shape. To avoid excessive false positives, CAD ignores the normal colon wall, including the haustra
Haustra
The haustra of the colon are the small pouches caused by sacculation, which give the colon its segmented appearance. The taenia coli runs the length of the large intestine...
l folds. In early clinical trials, CAD helped radiologists find more polyps in the colon than they found prior to using CAD.
Coronary artery disease
CAD is available for the automatic detection of significant (causing more than 50% stenosisStenosis
A stenosis is an abnormal narrowing in a blood vessel or other tubular organ or structure.It is also sometimes called a stricture ....
) coronary artery disease in coronary CT angiography (CCTA) studies. A low false positives rate (60-70% specificity per patient) allows using CAD as a screening device distinguishing between positive and negative studies and yielding a preliminary report. This, for example, can be used for chest pain patients' triage in an emergency setting.
Congenital heart defect
Early detection of pathology can be the difference between life and death. CADe can be done by auscultationAuscultation
Auscultation is the term for listening to the internal sounds of the body, usually using a stethoscope...
with a digital stethoscope and specialized software, also known as Computer-aided auscultation
Computer-aided auscultation
Computer-aided auscultation is a clinical decision support system, which is designed to assist physicians and other health professionals with decision making tasks when assessing a heart murmur. The need for computer-aided auscultation is increasing as the auscultation skills of physicians are...
. Murmurs, irregular heart sounds, caused by blood flowing through a defective heart, can be detected with high sensitivity and specificity. Computer-aided auscultation
Computer-aided auscultation
Computer-aided auscultation is a clinical decision support system, which is designed to assist physicians and other health professionals with decision making tasks when assessing a heart murmur. The need for computer-aided auscultation is increasing as the auscultation skills of physicians are...
is sensitive to external noise and bodily sounds and requires an almost silent environment to function accurately.