Scientific and market-specific presentations will deliver insights into cross-technology approaches, industry trends and processes. The agenda will feature interactive and interdisciplinary items to help you generate new solutions. A matchmaking tool provides a platform to search for potential partners based on profiles and interests. Participants MedTech Summit Partnering. Program MedTech Summit Congress. Login Sign-up. An outer electron will fill the vacant electron position and produce either a characteristic x-ray or an Auger electron.
These effects can be used for elemental detection through X-ray spectroscopy or Auger electron spectroscopy. Compton scattering is the predominant interaction between X-rays and soft tissue in medical imaging. Part of the energy of the photon is transferred to the scattering electron, thereby ionizing the atom and increasing the wavelength of the X-ray.
The scattered photon can go in any direction, but a direction similar to the original direction is more likely, especially for high-energy X-rays. The probability for different scattering angles are described by the Klein—Nishina formula. The transferred energy can be directly obtained from the scattering angle from the conservation of energy and momentum. Rayleigh scattering is the dominant elastic scattering mechanism in the X-ray regime. Whenever charged particles electrons or ions of sufficient energy hit a material, X-rays are produced.
X-rays can be generated by an X-ray tube , a vacuum tube that uses a high voltage to accelerate the electrons released by a hot cathode to a high velocity. The high velocity electrons collide with a metal target, the anode , creating the X-rays. In crystallography, a copper target is most common, with cobalt often being used when fluorescence from iron content in the sample might otherwise present a problem. When the electrons hit the target, X-rays are created by two different atomic processes:.
So, the resulting output of a tube consists of a continuous bremsstrahlung spectrum falling off to zero at the tube voltage, plus several spikes at the characteristic lines. The voltages used in diagnostic X-ray tubes range from roughly 20 kV to kV and thus the highest energies of the X-ray photons range from roughly 20 keV to keV. Both of these X-ray production processes are inefficient, with only about one percent of the electrical energy used by the tube converted into X-rays, and thus most of the electric power consumed by the tube is released as waste heat.
X-ray sources and effects
When producing a usable flux of X-rays, the X-ray tube must be designed to dissipate the excess heat. A specialized source of X-rays which is becoming widely used in research is synchrotron radiation , which is generated by particle accelerators.
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Its unique features are X-ray outputs many orders of magnitude greater than those of X-ray tubes, wide X-ray spectra, excellent collimation , and linear polarization. Short nanosecond bursts of X-rays peaking at keV in energy may be reliably produced by peeling pressure-sensitive adhesive tape from its backing in a moderate vacuum. This is likely to be the result of recombination of electrical charges produced by triboelectric charging. The intensity of X-ray triboluminescence is sufficient for it to be used as a source for X-ray imaging.
X-rays can also be produced by fast protons or other positive ions. The proton-induced X-ray emission or particle-induced X-ray emission is widely used as an analytical procedure. X-rays are also produced in lightning accompanying terrestrial gamma-ray flashes. The underlying mechanism is the acceleration of electrons in lightning related electric fields and the subsequent production of photons through Bremsstrahlung.
X-ray detectors vary in shape and function depending on their purpose.
X‐Ray Scattering Techniques Applied in the Development of Drug Delivery Systems
Imaging detectors such as those used for radiography were originally based on photographic plates and later photographic film , but are now mostly replaced by various digital detector types such as image plates and flat panel detectors. For radiation protection direct exposure hazard is often evaluated using ionization chambers , while dosimeters are used to measure the radiation dose a person has been exposed to.
X-ray spectra can be measured either by energy dispersive or wavelength dispersive spectrometers. For x-ray diffraction applications, such as x-ray crystallography , hybrid photon counting detectors are widely used. Projectional radiography is the practice of producing two-dimensional images using x-ray radiation.
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Bones contain much calcium , which due to its relatively high atomic number absorbs x-rays efficiently. This reduces the amount of X-rays reaching the detector in the shadow of the bones, making them clearly visible on the radiograph. The lungs and trapped gas also show up clearly because of lower absorption compared to tissue, while differences between tissue types are harder to see. Projectional radiographs are useful in the detection of pathology of the skeletal system as well as for detecting some disease processes in soft tissue.
Some notable examples are the very common chest X-ray , which can be used to identify lung diseases such as pneumonia , lung cancer , or pulmonary edema , and the abdominal x-ray , which can detect bowel or intestinal obstruction , free air from visceral perforations and free fluid in ascites. X-rays may also be used to detect pathology such as gallstones which are rarely radiopaque or kidney stones which are often but not always visible.
Traditional plain X-rays are less useful in the imaging of soft tissues such as the brain or muscle. One area where projectional radiographs are used extensively is in evaluating how an orthopedic implant , such as a knee, hip or shoulder replacement, is situated in the body with respect to the surrounding bone. This can be assessed in two dimensions from plain radiographs, or it can be assessed in three dimensions if a technique called '2D to 3D registration' is used.
This technique purportedly negates projection errors associated with evaluating implant position from plain radiographs. Dental radiography is commonly used in the diagnoses of common oral problems, such as cavities. In medical diagnostic applications, the low energy soft X-rays are unwanted, since they are totally absorbed by the body, increasing the radiation dose without contributing to the image.
Hence, a thin metal sheet, often of aluminium , called an X-ray filter , is usually placed over the window of the X-ray tube, absorbing the low energy part in the spectrum. This is called hardening the beam since it shifts the center of the spectrum towards higher energy or harder x-rays. To generate an image of the cardiovascular system , including the arteries and veins angiography an initial image is taken of the anatomical region of interest. A second image is then taken of the same region after an iodinated contrast agent has been injected into the blood vessels within this area.
These two images are then digitally subtracted, leaving an image of only the iodinated contrast outlining the blood vessels. The radiologist or surgeon then compares the image obtained to normal anatomical images to determine whether there is any damage or blockage of the vessel. Computed tomography CT scanning is a medical imaging modality where tomographic images or slices of specific areas of the body are obtained from a large series of two-dimensional X-ray images taken in different directions.
Fluoroscopy is an imaging technique commonly used by physicians or radiation therapists to obtain real-time moving images of the internal structures of a patient through the use of a fluoroscope. In its simplest form, a fluoroscope consists of an X-ray source and a fluorescent screen, between which a patient is placed.
However, modern fluoroscopes couple the screen to an X-ray image intensifier and CCD video camera allowing the images to be recorded and played on a monitor. This method may use a contrast material.
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Examples include cardiac catheterization to examine for coronary artery blockages and barium swallow to examine for esophageal disorders and swallowing disorders. The use of X-rays as a treatment is known as radiation therapy and is largely used for the management including palliation of cancer ; it requires higher radiation doses than those received for imaging alone.
X-rays beams are used for treating skin cancers using lower energy x-ray beams while higher energy beams are used for treating cancers within the body such as brain, lung, prostate, and breast.
Diagnostic X-rays primarily from CT scans due to the large dose used increase the risk of developmental problems and cancer in those exposed. Experimental and epidemiological data currently do not support the proposition that there is a threshold dose of radiation below which there is no increased risk of cancer. To place the increased risk in perspective, a plain chest X-ray will expose a person to the same amount from background radiation that people are exposed to depending upon location every day over 10 days, while exposure from a dental X-ray is approximately equivalent to 1 day of environmental background radiation.
An abdominal or chest CT would be the equivalent to 2—3 years of background radiation to the whole body, or 4—5 years to the abdomen or chest, increasing the lifetime cancer risk between 1 per 1, to 1 per 10, The risk of radiation is greater to a fetus, so in pregnant patients, the benefits of the investigation X-ray should be balanced with the potential hazards to the fetus.
Medical X-rays are a significant source of man-made radiation exposure. By , however, medical procedures in the United States were contributing much more ionizing radiation than was the case in the early s. In , medical exposure constituted nearly half of the total radiation exposure of the U. The increase is traceable to the growth in the use of medical imaging procedures, in particular computed tomography CT , and to the growth in the use of nuclear medicine.
Dosage due to dental X-rays varies significantly depending on the procedure and the technology film or digital. Depending on the procedure and the technology, a single dental X-ray of a human results in an exposure of 0. A full mouth series of X-rays may result in an exposure of up to 6 digital to 18 film mrem, for a yearly average of up to 40 mrem. Financial incentives have been shown to have a significant impact on X-ray use with doctors who are paid a separate fee for each X-ray providing more X-rays.
X-ray crystallography in which the pattern produced by the diffraction of X-rays through the closely spaced lattice of atoms in a crystal is recorded and then analysed to reveal the nature of that lattice. In the early s, experiments were done in which layers a few atoms thick of two different materials were deposited in a Thue-Morse sequence. The resulting object was found to yield X-ray diffraction patterns.
X-ray microscopic analysis, which uses electromagnetic radiation in the soft X-ray band to produce images of very small objects. X-ray fluorescence , a technique in which X-rays are generated within a specimen and detected.
The outgoing energy of the X-ray can be used to identify the composition of the sample. Industrial radiography uses X-rays for inspection of industrial parts, particularly welds. Authentication and quality control, X-ray is used for authentication and quality control of packaged items.