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Biliary Contrast Agents
The molecular structure of some iodinated contrast agents makes them suitable for the computer-tomographic examination of the biliary tract. Organic iodine compounds increase the attenuation of x-rays and the contrast between body tissues containing iodine and those tissues that do not contain iodine. The degree of opacification is directly proportional to the concentration and volume of the iodinated contrast agent (the total amount of iodine).
Biliary contrast agents can be taken orally, for example calcium iopodate, or intravenous meglumine iotroxate. The contrast media are excreted by the liver and concentrate in the gallbladder after passing the intrahepatic biliary tree and cystic duct.
Oral biliary contrast agents usually opacify the gallbladder after a few hours. If the gallbladder is removed, an intravenous cholegraphic agent is required and gallbladder CT can start 60 minutes after the beginning of contrast medium infusion.
The main limitation of the use of biliary contrast agents is the high rate of allergic reactions and of renal or hepatic toxicity. Caused by the potential for systemic toxicity with intravenous cholangiography, ultrasonography should be the preferred method for evaluation of the gallbladder and the bile ducts.
Breast Imaging
Breast imaging methods include mammography (mammogram), ultrasound, breast MRI, positron emission tomography, xeromammography, diaphanography and thermography.
Mammography is widely used as a screening method and diagnostic tool for breast cancer detection or evaluation of breast disease. Digital mammography takes multiple thin digital image 'slices' through the breast, which provides higher potential to see a small mass within dense tissue. The mammography quality standards act guarantees a high image quality.
Breast ultrasound (also called ultrasonography) should only be used as an additional imaging modality to evaluate specific breast abnormalities, especially to differentiate cystic from solid masses. Ultrasound is also used to guide needle breast biopsies.
Magnetic resonance imaging (MRI) is useful for breast MRI screening in cases of high cancer risk. In addition, multifocal breast cancer can be missed by standard practice mammography and can be early detected with breast MRI.
Diagnostic Imaging
Imaging refers to the visual representation of an object. Today, diagnostic imaging uses radiology and other techniques, mostly noninvasive, to create pictures of the human body. Diagnostic radiography studies the anatomy and physiology to diagnose an array of medical conditions. The history of medical diagnostic imaging is in many ways the history of radiology. Many imaging techniques also have scientific and industrial applications. Diagnostic imaging in its widest sense is part of biological science and may include medical photography, microscopy and techniques which are not primarily designed to produce images (e.g., electroencephalography and magnetoencephalography).
Brief overview about important developments:
Imaging used for medical purposes, began after the discovery of x-rays by Konrad Roentgen 1896. The first fifty years of radiological imaging, pictures have been created by focusing x-rays on the examined body part and direct depiction onto a single piece of film inside a special cassette.
In the 1950s, first nuclear medicine studies showed the up-take of very low-level radioactive chemicals in organs, using special gamma cameras. This diagnostic imaging technology allows information of biologic processes in vivo. Today, single photon emission computed tomography (SPECT) and positron emission tomography (PET) play an important role in both clinical research and diagnosis of biochemical and physiologic processes.
In the 1960s, the principals of sonar were applied to diagnostic imaging. Ultrasound has been imported into practically every area of medicine as an important diagnostic tool, and there are great opportunities for its further development. Looking into the future, the grand challenges include targeted contrast imaging, real-time 3D or 4D ultrasound, and molecular imaging. The earliest use of ultrasound contrast agents (USCA) was in 1968.
The introduction of computed tomography (CT/CAT) in the 1970s revolutionized medical imaging with cross sectional images of the human body and high contrast between different types of soft tissues. These developments were made possible by analog to digital converters and computers. First, spiral CT (also called helical), then multislice CT (or multi-detector row CT) technology expanded the clinical applications dramatically.
The first magnetic resonance imaging (MRI) devices were tested on clinical patients in 1980. With technological improvements including higher field strength, more open MRI magnets, faster gradient systems, and novel data-acquisition techniques, MRI is a real-time interactive imaging modality that provides both detailed structural and functional information of the body.

Today, imaging in medicine has been developed to a stage that was inconceivable a century ago, with growing modalities:
x-ray projection imaging, including conventional radiography and digital radiography;
scintigraphy;
single photon emission computed tomography;
positron emission tomography.

All these types of scans are an integral part of modern healthcare. Usually, a radiologist interprets the images. Most clinical studies are acquired by a radiographer or radiologic technologist. In filmless, digital radiology departments all images are acquired and stored on computers. Because of the rapid development of digital imaging modalities, the increasing need for an efficient management leads to the widening of radiology information systems (RIS) and archival of images in digital form in a picture archiving and communication system (PACS). In telemedicine, medical images of MRI scans, x-ray examinations, CT scans and ultrasound pictures are transmitted in real time.

See also Interventional Radiology, Image Quality and CT Scanner.
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