Microdose
Encyclopedia
Microdose refers to a category of radiology modalities
providing a very low radiation dose. These modalities are typically based on a photon-counting detector for capturing the image.
s when they are captured in a detector medium. This is in contrast to “pseudo-digital” detectors that integrates
photon energy over time, thus in practice measuring an analog signal
that in turn is digitized
. While the conversion steps from analog to digital signal in a traditional detector introduces thermal noise, quantization errors
and loss of information during signal processing, a truly digital detector suffers from none of these weaknesses. A photon-counting detector is capable of capturing close to all information in the signal. This way it is possible to lower the radiation dose to a minimum while preserving or even improving image quality.
system from Medical imaging supplier Sectra, mainly targeted for intense breast screening
programs. Breast examinations is one of the most demanding with respect to image quality, as early detection of cancerous changes relies on finding micro-calcifications
in the breast tissue. These tiny structures can be perceived by a trained eye, but only as far as the image quality allows. At the same time, the significance of low dose comes particularly apparent in screening programs, as a large part of a population is targeted.
The Sectra system uses silicon
as detector medium, where a large array of very thin silicon sticks constitutes the pixel
s in the photon-counting detector. Another detector system under development by XCounter uses Cadmium Telluride
as a detector medium.
Medical imaging
Medical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...
providing a very low radiation dose. These modalities are typically based on a photon-counting detector for capturing the image.
Photon-counting Detector
A photon-counting detector utilizes the discrete nature of X-rays, as it counts individual photonPhoton
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s when they are captured in a detector medium. This is in contrast to “pseudo-digital” detectors that integrates
Integral
Integration is an important concept in mathematics and, together with its inverse, differentiation, is one of the two main operations in calculus...
photon energy over time, thus in practice measuring an analog signal
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
that in turn is digitized
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
. While the conversion steps from analog to digital signal in a traditional detector introduces thermal noise, quantization errors
Quantization error
In analog-to-digital conversion, the difference between the actual analog value and quantized digital value is called quantization error or quantization distortion. This error is either due to rounding or truncation...
and loss of information during signal processing, a truly digital detector suffers from none of these weaknesses. A photon-counting detector is capable of capturing close to all information in the signal. This way it is possible to lower the radiation dose to a minimum while preserving or even improving image quality.
Uses
There are today very few commercially available Microdose modalities. The first to hit the market was a mammographyMammography
Mammography is the process of using low-energy-X-rays to examine the human breast and is used as a diagnostic and a screening tool....
system from Medical imaging supplier Sectra, mainly targeted for intense breast screening
Breast cancer screening
Breast cancer screening refers to the medical screening of asymptomatic, apparently healthy women for breast cancer in an attempt to achieve an earlier diagnosis. The assumption is that early detection will improve outcomes...
programs. Breast examinations is one of the most demanding with respect to image quality, as early detection of cancerous changes relies on finding micro-calcifications
Dystrophic calcification
Dystrophic Calcification is the calcification occurring in degenerated or necrotic tissue, as in hyalinized scars, degenerated foci in leiomyomas, and caseous nodules. This occurs as a reaction to tissue damage, including as a consequence of medical device implantation.Dystrophic calcification can...
in the breast tissue. These tiny structures can be perceived by a trained eye, but only as far as the image quality allows. At the same time, the significance of low dose comes particularly apparent in screening programs, as a large part of a population is targeted.
The Sectra system uses silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
as detector medium, where a large array of very thin silicon sticks constitutes the pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
s in the photon-counting detector. Another detector system under development by XCounter uses Cadmium Telluride
Cadmium telluride
Cadmium telluride is a crystalline compound formed from cadmium and tellurium. It is used as an infrared optical window and a solar cell material. It is usually sandwiched with cadmium sulfide to form a p-n junction photovoltaic solar cell...
as a detector medium.
See also
- MammographyMammographyMammography is the process of using low-energy-X-rays to examine the human breast and is used as a diagnostic and a screening tool....
- Medical ImagingMedical imagingMedical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...
- X-rayX-rayX-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
- Semiconductor detectorSemiconductor detectorThis article is about particle detectors. For information about semiconductor detectors in radio, see Diode#Semiconductor_diodes, rectifier, detector and cat's-whisker detector....
- Scintillation counterScintillation counterA scintillation counter measures ionizing radiation. The sensor, called a scintillator, consists of a transparent crystal, usually phosphor, plastic , or organic liquid that fluoresces when struck by ionizing radiation. A sensitive photomultiplier tube measures the light from the crystal...