Understanding X-Rays: A Synopsis of Radiology

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The difficulty of interpreting these images is due to this superimposition of structures, and thus pathologic processes may appear less defined.


  1. Start Here.
  2. Chapter 5: Radiological anatomy.
  3. What Happens During an X-ray??
  4. Roentgen's discovery of the x-ray.

Traditional radiography systems use a film-screen combination consisting of a cassette, one or two intensifying screens, and a sheet of film. The film is simply thin plastic with a photosensitive emulsion coated onto one or both sides.

What Is an X-Ray?

The cassette is designed to protect the film from ambient light before exposing the film with x-rays. For routine radiography, double-screen, double-emulsion film-screen combinations are often used to improve sensitivity and reduce radiation exposure.

Radiographic views are named by the direction of the x-ray beam from the source to the imaging recording device. Several different systems are currently available for the acquisition of digital radiographs: the ones most commonly seen in clinical use are computed radiography CR , charged-coupled devices CCDs , direct detection flat panel systems, and indirect detection flat panel systems. The workflow of CR systems is similar to that with conventional screen-film radiography. The CR imaging plate is made of barium fluorobromide or barium fluoride barium fluorohalide. The CR imaging plate traps the x-ray beam the electron within the phosphor layer, and this electromagnetic energy is stored until processing.

The CR plate is inserted into a reader that contains a laser that scans across the imaging plate, releasing the stored energy causing the emission of light. These light emissions are read by a photodiode scanning the imaging plate. The prime advantage of CR over film-screen radiography is the increase in dynamic range. The system can tolerate a wider exposure range and thus result in a smaller number of diagnostically inadequate films. However, the raw data require processing algorithms to produce clinically useful images.


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  • Charged couple devices CCDs detectors form images from visible light. The surface of a CCD chip is photosensitive, and when a pixel is exposed to light, electrons are produced and built up within the pixel. This technology is used in modern video and digital cameras. Dorcas P.

    Radiography

    Radiography and ultrasonography are important diagnostic tools in the field of reptile medicine Silverman and Janssen, In order to apply radiography and ultrasonography effectively, it is essential to know the normal anatomy of the reptile species being evaluated. Most reptiles do not require anesthesia for radiography. Snakes may be placed inside a Plexiglas tube to obtain dorsoventral and lateral views.

    Radiography is primarily useful to evaluate the skeletal system in snakes and to identify disease processes involving the respiratory tract. With radiography alone, visceral organs are often difficult to discern. Contrast studies are of great diagnostic value in cases of gastrointestinal disease and for identification of foreign bodies and masses. In chelonians, as in snakes, radiographs are most helpful in evaluating the respiratory and skeletal systems. Craniocaudal views are obtained in addition to the standard views in order to fully appreciate the respiratory tract.

    In lizards and crocodilians, radiography is a useful tool to evaluate skeletal changes e. Female prehensile-tailed skink Corucia zebrata with coelomic effusion A caused by a ruptured follicle, and postoperative view B ,. Soft tissue changes often can be better demonstrated with the use of ultrasonography. Most reptiles can be examined with manual restraint alone. As is the case with radiography, knowledge of the normal anatomy and pathophysiology of disease is essential to diagnose abnormalities. Also, biopsies of visceral organs or masses can be more safely obtained with ultrasound guidance.

    Radiography continues to be used in basic post-EVAR surveillance despite the availability of advanced imaging modalities. It is applied as an adjunct investigation method for the detection of structural changes of the stent-graft that might be missed on CTA. Radiography is considered by some authors to be superior to CTA in this regard [20]. Any protocol should include antero-posterior and lateral acquisitions for depiction of stent-graft migration and component separation as well as oblique acquisition able to detect wire fractures, although the clinical importance of the later is not fully elucidated.

    It is preferable to perform radiography prior to same-day CT examination so that excreted contrast material in the collecting system does not obscure the stent-graft [21]. Radiography is the oldest modality used in the evaluation of urinary tract disease, but its utility is limited.


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    • The normal urinary tract is not sufficiently distinct from other abdominal and pelvic structures to be properly evaluated using radiography alone. There may, however, be cases in which there is sufficient retroperitoneal fat to outline the kidneys on plain radiographs and even assess their relative sizes.

      A renal mass or severely hydronephrotic kidney might be detected by the presence of a soft tissue mass, calcification or fat, and displacement of adjacent structures Figure A full bladder can also be seen as a midline structure in the pelvis, which will occasionally displace bowel loops out of the pelvis Figure Figure Radiograph of the abdomen demonstrates soft-tissue density in the region of the left renal fossa with displacement of bowel arrows.

      A renal cell carcinoma was discovered on cross-sectional imaging.

      X-Ray vs. CT vs. MRI

      Radiograph of the abdomen demonstrates soft tissue in the pelvis displacing bowel out of the pelvis arrows. Ultrasound demonstrated that a full bladder was the cause of the imaging findings. Calculi in the urinary collecting system can at times be seen on radiography depending on their composition — Figure Nephrocalcinosis, cortical or medullary, can also be detected depending on the degree of involvement.

      Radiograph of the abdomen demonstrates a calcific density in the region of the right renal fossa arrows.

      Discrepancy and Error in Radiology: Concepts, Causes and Consequences

      A staghorn calculus was found on ultrasound. Incidental note was made of a tripediculate vertebra in the lower lumbar spine. Radiographs can also be beneficial in determining the correct positioning of various drainage catheters and stents. Ureteral stents in particular can migrate, thereby mitigating their effectiveness. Most catheters and stents are sufficiently radioopaque to be visible on radiographs Figure A , Radiograph of the abdomen demonstrates double J stents overlying the urinary tracts. Proximal and distal loops overlie the renal pelves and bladder, respectively, although the ureteral courses appear tortuous.

      B , Several days later, both stents have changes in position most evident on the right, where the proximal aspect of the stent appears to be in the right ureter arrow. Overall, however, the role of radiography has largely been supplanted by the cross-sectional imaging modalities ultrasound, CT, and MRI and by nuclear medicine.

      Segebade, in Encyclopedia of Materials: Science and Technology , Radiography using ionizing radiations is one of the most important tools in the examination of art objects. Based on the differential absorption of radiation the technique has been regularly applied to a variety of art objects made of paper, wood, ceramics, and heavy metal castings and also to mummified remains excavated from archaeological sites.

      The generation of flat two dimensional images by this technique is called projectional radiography. In computed tomography CT scanning an X-ray source and its associated detectors rotate around the subject which itself moves through the conical X-ray beam produced. Any given point within the subject is crossed from many directions by many different beams at different times. Information regarding attenuation of these beams is collated and subjected to computation to generate two dimensional images in three planes axial, coronal, and sagittal which can be further processed to produce a three dimensional image.

      Since the body is made up of various substances with differing densities, Ionising and non-ionising radiation can be used to reveal the internal structure of the body on an image receptor by highlighting these differences using attenuation , or in the case of ionising radiation, the absorption of X-ray photons by the denser substances like calcium -rich bones.

      The discipline involving the study of anatomy through the use of radiographic images is known as radiographic anatomy. Medical radiography acquisition is generally carried out by radiographers , while image analysis is generally done by radiologists. Some radiographers also specialise in image interpretation. Medical radiography includes a range of modalities producing many different types of image, each of which has a different clinical application. The creation of images by exposing an object to X-rays or other high-energy forms of electromagnetic radiation and capturing the resulting remnant beam or "shadow" as a latent image is known as "projection radiography.

      Bone and some organs such as lungs especially lend themselves to projection radiography.

      Learn more about Radiography

      It is a relatively low-cost investigation with a high diagnostic yield. The difference between soft and hard body parts stems mostly from the fact that carbon has a very low X-ray cross section compared to calcium. Computed tomography or CT scan previously known as CAT scan, the "A" standing for "axial" uses ionizing radiation x-ray radiation in conjunction with a computer to create images of both soft and hard tissues.

      These images look as though the patient was sliced like bread thus, "tomography"-- "tomo" means "slice".

      "Introduction to Pediatric Chest Radiography" by George Taylor for OPENPediatrics

      Though CT uses a higher amount of ionizing x-radiation than diagnostic x-rays both utilising X-ray radiation , with advances in technology, levels of CT radiation dose and scan times have reduced [2]. CT exams are generally short, most lasting only as long as a breath-hold, Contrast agents are also often used, depending on the tissues needing to be seen. Radiographers perform these examinations, sometimes in conjunction with a radiologist for instance, when a radiologist performs a CT-guided biopsy. DEXA , or bone densitometry, is used primarily for osteoporosis tests.