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Medical imaging

Introduction

QuestionAnswer
Define radiology. A branch of medicine concerned with the use of radiant energy or radioactive material in the diagnosis and treatment of disease.
How are X-rays produced? In an X-ray tube by focusing a beam of high-energy electrons onto a tungsten target.
How does an X-ray produce an image? Tissues of high density cause more X-ray beam attenuation and are shown as lighter grey or white on a radiograph. Less dense tissues and structures cause less attenuation of the X-ray beam and appear darker on radiographs.
What colour does air appear on an X-ray? Black.
What colour does fat appear on an XR? Very dark grey.
What colour does soft tissue appear on an XR? Grey.
What colour does bone appear on an XR? Very light grey.
What colour does metal appear on an XR? White.
How many planes should you take an XR? At least two.
What is an AP view? Anteroposterior.
What is a PA view? Posterior-Anterior
Why is PA sometimes preferred? It does not magnify the heart as much from behind, so gives a more accurate representation.
What is a mammography? A specific type of XR that uses a low does of XR system designed for creating detailed images of the breast.
When is mammography used? As a screening tool to detect early breast cancer in women without signs or symptoms of disease. Or to diagnose a breast disease in women with symptoms such as a lump, pain or nipple discharge.
What is fluoroscopy? A type of medical imaging that shows a continuous XR image on a monitor.
When is a fluoroscopy used? When real time examination of the patient's body is required. E.g. orthopaedic implants during surgery, catheters and pacemakers.
What is an angiography? An XR technique used in the examination of the arteries, veins and organs to diagnose blockages.
What occurs in an angiogram? The radiologist inserts a thin tube, called a catheter, into an artery or vein from an access point (arm or groin). A substance called a contrast agent is injected to make the blood vessels visible on the XR image.
Define tomography. A method that produces images of single tissue plane.
What does CT and CAT stand for? Computed tomography and Computerized axial tomography.
What does a CT scan produce? Cross-sectional images or "slices" of anatomy.
What are the advantages of CAT scans? Fast. Readily available. Good imaging of bony structures, abdomen and lungs.
What are the disadvantages of CAT scans? High radiation. Not so good at imaging soft tissue such as brain and spinal cord.
What is nuclear medicine also known as? Scintigraphy.
How does scintigraphy work? Uses gamma radiation to form images following the injection of various radiopharmaceuticals.
What is the most common radionuclide? Technetium.
What does metastable mean? Means that the technetium atom has two basic energy states: high and low.
What happens as the technetium transforms energy states? As the technetium transforms from the high-energy state to the low-energy state, it emits a quantum energy in the form of a gamma ray.
What happens when the gamma ray is emitted? Gamma rays emitted by the radionuclides are detected by a gamma camera that converts that absorbed energy of the radiation to an electrical signal. The signal is analysed by a computer and displayed as an image.
What are the main advantages of scintigraphy? High sensitivity and providing functional information as well as anatomical information.
What does SPECT stand for? Single photon emission CT.
What is SPECT? A scintigraphic technique whereby the computer is programmed to analyse data coming from a single depth within the patient.
Why is SPECT good? It allows greater sensitivity in the detection of subtle lesions overlain by other active structures.
Why would you combine SPECT with CT? Fuses highly sensitive SPECT findings with anatomically accurate CT images, thus improving sensitivity and specificity.
What does PET stand for? Positron emission tomography.
What is PET? A combination of computed tomography and scintillation scanning most commonly used in oncology.
What are the advantages of scintigraphy? Good functional information. Good localization of pathology.
What are the disadvantages of scintigraphy? High radiation dose. Not so good at differentiating between different pathologies.
What MRI stand for? Magnetic Resonance Imaging.
What is the principle of MRI? Uses a powerful magnetic field and radio frequency pulses to produce detailed images of the body's internal structures as cross-sectional images or slices.
How does MRI work?
Created by: robertspedding