山东第一医科大学（泰山医学院）：《医学影像学》课程教学资源（授课教案）2.Radiolgy overview 2.doc_大学文库

1 Teaching Plan Name：Chuan LU Academic Year：2012-2013 Term :2 Date.March 8, Period：3-4 Textbook Diagnostic Imaging Specialty and Stratification 2010 MBBS autumn (international students) Content Radiology & Diagnostic Imaging Overview 2 Teaching hours 2 Objectives To master the principles of CT and MR Key points Production of CT and MR imaging Points difficult to understand Special terms used on CT and MR reports Content for self study MR Sequences Teaching equipment multimedia Related knowledge MR contrast agent Teaching methods Heuristic method /discuss Outlines, requirements and time allocation Computed Tomography (CT) Defined A painless, noninvasive diagnostic x-ray procedure using ionizing radiation that produces a cross-sectional image of the body General Principles of CT ⚫ Computed tomogaraphy is a special type of X-ray procedure that involves the indirect measurement of weakening ,or attenuation, of x -rays at numerous position located the patient being investigated ⚫ Uses x-rays and computer generation of images ⚫ Image formed using a rotating thin beam(s) of ionizing radiation ⚫ Image “slices” reconstructed by computation ⚫ The image formed is related to the subjects density ⚫ Image display on computer or multiple films ⚫ New technology is multislice helical scanner Computed Tomography ⚫ Computed Tomography is a specialized X-ray imaging technique. ⚫ It may be performed "plain" or after the injection of a "Contrast Agent". CT x-ray tube moves around the patient. The detectors may remain stationary or may move around the patient as in this diagram. The gantry can be angled. Detectors receive the transmitted x-rays and turn them into electrical signals. These signals are digitized and fed into a computer. The computer processes the numerical data using a mathematical algorithm to form an image. ⚫ A computer then processes this information to create an image on the video screen. ⚫ These images are called "sections" or "cuts" because they appear to resemble cross-sections of the body. ⚫ These images are called "sections" or "cuts" because they appear to resemble cross-sections of the body 10’ 10’

2 Outlines, requirements and time allocation Computed Tomography ⚫ Don't worry though, the patient is not actually "cut". Because it does use X-Rays to form the image, this computerized technique has some limitations that are similar to those for plain film radiographs ⚫ CT solves the problem of superimposition by allowing the clinician to view a series of thin sections, 1.5 to 10 mm thick depending on the anatomic region, completely through the area of interest. ⚫ Each layer can be viewed sequentially so the clinician can determine the full extent of the pathology. With CT, axial or cross-sectional images are made routinely because of the arrangement of the detectors around the patients body and the computer processing of the detector signals. Each layer can be viewed sequentially so the clinician can determine the full extent of the pathology Axial View ⚫ Other imaging planes can be obtained directly by repositioning the patient within the scanner or by tilting the gantry, the donut-shaped portion of the scanner that houses the x-ray scanner and detectors. ⚫ CT imaging also be used to differentiate soft tissue from bone, and various types of soft tissue from each other. Thus, tumors can be distinguished from normal tissue parenchyma because the neoplastic process causes enough tissue change to be detectable on CT . Special terms used on CT reports: ⚫ High attenuation (light or white)-Bone Synonyms: High density, hyperdense ; ⚫ Low Attenuation (dark or black)-Gas Synonyms: Low density, hypodense ⚫ Pre-contrast (Unenhanced ) CT , CT ⚫ Contrast CT (Enhanced CT) -white , CT ⚫ Hounsfield Units (Inventor of CT) CT-contrast CT /enhanced CT After the intravenous administration of contrast medium (iodine), the contrast medium goes to the any organs where there are vessels and blood. The organs and vessels will become white-high attenuation CT Values ⚫ Hounsfield units (HU) = CT numbers = Arbitrary scale based on attenuation values with water assigned a CT number of 0 ⚫ One CT no. (HU)=1/1000 of the water attenuation value= 0.1% change in attenuation relative to water ⚫ -1,000 -> 0 -> + 1000 ⚫ air water dense bone CT- Advantages ⚫ Tremendous Density Resolution (1500x Better Than X-ray) - Sensitive to slight density difference ⚫ Cross sectional anatomy This technique eliminates the problem of conventional X-rays, where all the shadows overlap ⚫ Attenuation: reduction in intensity of x-ray beam as it traverses matter either by absorption or deflection ⚫ Multiple Plane Reconstruction ⚫ CT Angiography ⚫ High-Resolution 15’ 15’

3 Outlines, requirements and time allocation False Aneurysm of the Internal Carotid Artery The Dual Volume reconstruction of the same 3D dataset shows the carotid sheath in place and the relationship of the stents to the calcified wall of the aneurysm and to the endoleak INTERPRETATION OF HIGH-RESOLUTION (HRCT) CHEST CT -BRONCHIECTASIS ⚫ Traction bronchiectasis refers to bronchial dilation that occurs in patients with lung fibrosis or distorted lung architecture. Traction on the bronchial walls due to fibrous tissue reults in irregular bronchial dilation (bronchiectasis). Usually segmental and subsegmental bronchi are involved, but small periperhal bronchi or bronchioles may also be affected. Commonly associated with honeycombing MAGNETIC RESONANCE IMAGING (MRI) Defined： A noninvasive scanning procedure that provides visualization of fluid, soft tissue, and bony structures without the use of radiation ⚫ Tube shaped machine ⚫ Uses a magnetic field and radio frequency waves. Body chemical composition and tissue structure contribute to form image contrast. Computer generated image MRI-Principle ⚫ Most of the MRI procedures use the H+ (proton) as the body chemical to create an image. H+ distributed widely in tissue water (either free in nature like blood, body fluid or in bound form like water in cells). MRI-Principle ⚫ The nuclei spin around their axis, acting like a small bar magnet, in random directions in the tissue. When the body is placed in the MRI machine, some of the randomly arranged nuclei will line up along the direction of the static magnetic field produced by MRI machine. Then radio-frequency pulse is given, the precession of the spinning atoms increases, going to a high energy state. After the radio-frequency pulse is turned off, the axis of the high energy nuclei will return back to normal (relax time) and release the excess energy to produce signals. These signals are collected, evaluated and reconstructed in the computer, then forming and displaying the images Magnetic Resonance Imaging ⚫ Also called “MRI” (used to be NMRI) ⚫ Image formed by transmitting and receiving radio waves inside a high magnetic field ⚫ Image “slices” reconstructed by computation ⚫ The image formed is related to: ⚫ Scanner settings ⚫ Patient hydrogen density ⚫ Patient hydrogen chemical/physical environment ⚫ Image display on computer or multiple films MRI ⚫ Large Magnetic Field, RF (MHz range) ⚫ Measure proton Resonance ⚫ Cross-sectional Anatomy ⚫ Sensitivity vs. Specificity ⚫ Flow Imaging (MR Angiography) ⚫ Speed and Resolution ~ CT 10’ 10’