Radiologic Tests

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  RADIOLOGIC TESTS Radiologic Tests Introduction to Radiologic Tests Learning to evaluate radiographic tests is essential for excellent patient care. A thorough knowledge of anatomy and pathology is essential in this pursuit. Computed Tomography (CT) Scan CT is a more sensitive x-ray detection system which creates slice images through the body. The x-ray tube and detectors rotate around the patient, and a computer system manipulates the data. The data can be reconstructed to create axial (transverse), sagittal, coronal, and 3 -D views. When looking at an axial CT, imagine you are standing at the patient's feet looking toward their head. Different window settings on the computer allow you to view certain structures better (e.g.  bone window lung window) IV and oral contrast can be used to evaluate arteries, veins and gastrointestinal structures in more detail. Fluoroscopy A continuous beam of x-rays passes through the patient and gives a moving, real-time image;  basically a moving x-ray. Used in gastrointestinal barium and other contrast studies, angiography, and most interventional radiology procedures. Commonly used intra-operatively in orthopedic surgery and neurosurgery. Magnetic Resonance Imaging (MRI) The patient is placed within the bore of a powerful magnet that passes radio waves though the body in a particular series of very short pulses. Each pulse causes a responding pulse to  be emitted from the patient. A computer manipulates the data which produces an image. Contrast may be used to evaluate certain conditions. Different sequences include T1 in which fluid appears dark and T 2 in which fluid appears bright white. The benefits to the MRI include no radiation exposure and it provides more soft tissue detail. The cons to MRI include expense, contraindicated if the patient has metal hardware implanted or a pacemaker takes longer than a CT, motion interference can distort images, claustrophobic or severely anxious patient may not be able to tolerate scan, morbidly obese may not be able to fit in the scanner.  Radionuclide Imaging (Nuclear Imaging) Uses radiolabeled isotopes (radionuclide) attached to normal physiologic chemical substances to visualize  particular living organs and tissues. An image is obtained because the isotope emits gamma rays for a brief  period of time which are detected by special cameras. Technetium-99m (99mTc) : Most commonly used nuclide. Used in ionic form to detect a Meckel diverticulum , or attached to organic phosphate for a bone scan. It can even be attached to patient's own RBCs or WBCs. Positron Emission Tomography (PET) Scan: Uses short-lived positron emitting isotopes most commonly attached to a glucose analogue to detect areas of increased metabolic activity. Most common use is evaluating for staging solid tumors and evaluating metastasis. PET can be fused with a CT scan to precisely localize lesions. Ultrasound (US) Very high frequency sound is directed into the body from a transducer placed in contact with the skin. The sound is reflected by tissue to produce echoes picked up from the same transducer and converted into an electrical signal which produces 2 -D or 3 -D images. Ultrasound is a less expensive test that does not expose the patient to radiation. The test is useful for obstetrical, gynecological, pediatric, and testicular conditions, determining cystic (black) vs. solid (grey) structures. US can also produce moving images and can  be done at the bedside. Ultrasound takes longer than a CT scan, results are operator dependent, it is not useful for bone or lung since these entities almost completely absorb the ultrasound beam. Doppler US:  Sound reflected from a mobile structure shows a variation in frequency that corresponds to the speed of movement. The shift in frequency can be turned into an audible signal (e.g. fetal heartbeat) Flow can also be shown as the frequency changes depending on the direction of the flow in relation to the transducer. This is illustrated by colors on the screen with red signifying flow toward the transducer and  blue signifying flow away from the transducer. Examples of US exams : Echocardiography, obstetrical US , premature infant head US , suspected abdominal aortic aneurysm (AAA) or deep vein thrombosis (DITT) , gallbladder US , trauma (focused assessment with sonography for trauma or FAST exam) , pelvic US , breast US , testicular US , carotid US  X-rays There are five basic densities on an x-ray Air - Will appear black Bone -Will appear white Fat - Denser than air but less dense than soft tissues Soft Tissue -Denser than fat but less dense than bone X-rays are absorbed to a variable extent as they pass through the body. This difference in absorption  produces an image. The projection is described by the  path of the x-ray beam (e.g. in a PA or posteroanterior film the x-ray beam went through the patient's back initially) An x-ray will only produce 2 -D images, therefore perpendicular views may need to be obtained. Always consider x-ray before a CT or MRI. Specific Radiologic Tests Abdominal CT Commonly used with oral and IV contrast to evaluate trauma, appendicitis, pancreatitis, diverticulitis , kidney stones  (without contrast), and determine stages of cancer. Abdominal Ultrasound Used to rapidly evaluate the liver , gallbladder (gallstones, cholecystitis ) , appendix, pancreas, and abdominal aortic aneurysms. Abdominal X-rays (Kidney Ureter Bladder or KUB) The KUB is an x-ray of the abdomen taken in anteroposterior or AP direction. It is commonly ordered in patients complaining of abdominal pain. An abdominal x-ray can help identify foreign bodies, ileus, malrotation, small bowel obstruction with air-fluid levels, and volvulus. It can also detect perforation with free-air under the diaphragm or within structures air should not normally be (e.g. intestinal wall or biliary tract) but the upright chest x-ray is the better test .  Arthrography Imaging following the injection of contrast (iodinated or air) into a joint to highlight the soft tissue structures by coating their surfaces. It is used most often to define intra-articular structures or to confirm intra-articular needle placement when joint aspiration is performed. Typically, contrast material is injected in a joint using fluoroscopic guidance; the joint is then subjected to further imaging with either CT or MRI. Barium Enema A barium enema is a test in which barium sulfate is placed into the patient's rectum in order to evaluate the colon. X-rays are taken which will outline the location of the barium in the colon. Patients undergo a bowel prep the night before with laxatives such as polyethylene glycol in order to clean out the patient thoroughly for the examination, as is also done before procedures such as colonoscopies. Barium Swallow The patient is given barium to swallow while the esophagus is imaged via fluoroscopy. Used to evaluate esophageal pathology , aspiration, and swallowing abnormalities. In a modified barium swallow  different consistencies of barium are swallowed by the patient. X-rays are taken to monitor for aspiration. This helps determine what types of foods are safe for the patient to eat. Bone X-ray X-rays of the bones are ordered primarily to detect fractures. They may also help diagnose osteomyelitis which may be visualized as an elevation of the periosteum. Chest CT Allows for detailed images of the chest cavity. Indications may include pneumonia, lung nodules, pneumothorax, pulmonary embolism  and rib fractures.
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