X ray radiography

Medical imaging Medical imaging: The technique and process of creating visual representations of the interior of a body for clinical analysis and medical intervention. Medical imaging seeks to reveal internal structures hidden by the skin and bones, as well as to diagnose and treatdisease. Medical imaging also establishes a database of normalanatomyandphysiologyto make it possible to identify abnormalities.

Types of medical imagingIt incarporated radiology which uses imaging technologies of :

X-ray radiographyMagnetic resonance imagingMedical ultrasonography (ultrasound)EndoscopyElastographyTactile imagingThermographyMedical photographyPositron emission tomography

X-ray radiography

Types of X-Ray radiography :Dental ImagingPlain film radiography : All X-ray photons passing through patient, easily go through the film without interaction, but they are caught by the high-Z phosphor screen.This screen absorbs the X-rays and gives out fluorescent light exposing the film. The film is subsequently processed to form a final image.

(2) PSP-photo-stimulable phosphor (indirect system): This application uses psp plate to capture and store a latent radiographic image. After exposure to x-rays, excited electrons in the phosphor material on the plate remain trapped in the crystal lattice. The laser beam within the scanning unit stimulates the phosphor crystals, releasing the trapped electrons, and light is emitted in proportion to the amount of radiation absorbed by the phosphor crystals. This light is then converted into a digital image.

Types of X-Ray radiography :Dental Imaging(3) CCD-Charge-Coupled Device (direct system):In a CCD for capturing images, there is a photoactive region (anepitaxiallayer of silicon), and a transmission region made out of a shift register. An image is projected through alensonto the capacitor array (the photoactive region), causing each capacitor to accumulate an electric charge proportional to thelightintensity at that location. A control circuit causes each capacitor to transfer its contents to its neighbor (operating as a shift register). The last capacitor in the array dumps its charge into acharge amplifier, which converts the charge into avoltage. The sequence of voltages are then sampled, digitized, and usually stored in memory. Charge packet transfer

Types of X-Ray radiography :Dental Imaging(4) CMOS-Complementary Metal Oxide Semiconductor(direct system)It is composed of: An array of identical pixels, each having at least a photodiode and an addressing transistor, A Y-addressing or scan register to address the sensor line-byline, by activating the in-pixel addressing transistor. A X-addressing or scan register to address the pixels on one line, one after another. An output amplifier.

Types of CMOS Pixel architectures :1. Passive Passive cmos pixel based on one in-pixel transistor, RS used as the row selection switch At the beginning of an exposure the photodiode is reverse biased to a high voltage (e.g. 3.3 V). During the exposure time, impinging photons decrease the reverse voltage across the photodiode. At the end of the exposure time the remaining voltage across the diode is measured, and its drop from the original value is a measure for the amount of photons falling on the photodiode during the exposure time. To allow a new exposure cycle, the photodiode is reset again.

Active cmos pixel based on in-pixel amplifier. The transistor RST and RS are used for resetting and selection of the pixelTypes of CMOS Pixel architectures :2. Active The pixel is composed out of the photodiode, the reset transistor, the driver of the source-follower and the addressing transistor. The current source of the source-follower is placed at the end of the column busThe photodiode is reverse biased or reset. Impinging photons decrease the reverse voltage across the photodiode.At the end of the exposure time the pixel is addressed and the voltage across the diode is brought outside the pixel by means the source-follower.The photodiode is reset again..

PPD cmos pixel based on in-pixel amplifier in combination with pinned photodiode. RST , RS , TX are respectively the reset row select and transfer transistor To pixel of APS sensor, an extra (pinned) photodiode is added which is connected to the readout circuit by means of an extra transfer gate, TX. With this pixel the photodiode is separated from the readout node. It operates as follows :Conversion of the incoming photons is done in the (pinned) photodiode.At the end of the exposure, the readout node is reset by the reset transistor.A first measurement is done of the output voltage after reset.The photodiode is emptied by activating TX and transferring all charges from the photodiode to the readout node.A second measurement is done of the output voltage after transfer.The two measurements are subtracted from each other (correlated double sampling, CDS)

Types of CMOS Pixel architectures :3. PPD

Improvement flow in CMOS Pixel architectures1. In passive cmos pixel, due to the mismatch between the small pixel capacitance and the large vertical bus capacitance; pixel suffered from large noise level.2. To overcome above issue; concept of active pixel was introduced, in which every pixel gets its own in-pixel amplifier, being a source follower. Unfortunately, the kTC noise component, introduced by resetting the photodiode, still remained.3. To solve the latter issue of thermal FET noise in the presence of a filtering capacitor, the so-called pinned photodiode pixel was introduced.

CMOS Vs. CCD

CMOS Vs. CCDCMOS sensor has higher responsivity than CCD.Dynamic range, noise level hence image quality is better in CCD than CMOS sensorCMOS sensor has superior ability for windowing, i.e. the ability to read out the portion of the image sensor. CMOS imagers operate with single bias voltage and clock level, CCD typically require few higher voltage biases but clocking has been simplified in modern devices that operate with low voltage clocks.CMOS is the technology of choice for high-volume, space constrained applications where image quality requirements are low. This makes them a natural fit for security cameras, PC videoconferencing, wireless handheld device videoconferencing, bar-code scanners, fax machines, consumer scanners, toys, biometrics and some automotive invehicle uses. CCD remain the most suitable technology for high-end imaging applications, such as digital photography, broadcast television, high-performance industrial imaging, and most scientific and medical applications.

Scintillator The scintillation process in inorganic materials is due to the electronic band structure found in crystals and is not molecular in nature as is the case with organic scintillators. An incoming particle (X ray photons)can excite an electron from the valence band to either the conduction band or the exciton band (located just below the conduction band and separated from the valence band by an energy gap. This leaves an associated hole behind, in the valence band. Impurities create electronic levels in the forbidden gap. The excitons are loosely bound electron-hole pairs which wander through the crystal lattice until they are captured as a whole by impurity centers. The latter then rapidly de-excite by emitting scintillation light

FOPThe FOP is an optical device comprised of a bundle of micron-sized optical fibers. The FOP is used as a lens to convey the light and image with high efficiency and low distortion. Unlike a normal optical lens, no focusing distance is required

CMOS DENTAL SENSORCMOS DENTAL SENSOR ARCHITECTURE: SCINTILLATOR + FOP + CMOS CHIPCMOS DENTAL SENSOR WORKING MECHANISM : X RAY incident on scintillator are converted to light signal. Light is transported through FOP to CMOS chip. Light incident on CMOS chip is coverted to electronic digital signal which produces the final image

USB INTERFACEUniversal Serial Bus (USB) is a set of interface specifications for high speed wired communication between electronics systems peripherals and devices with or without PC/computer.USB 2.0, also known as hi-speed USB. This hi-speed USB is capable of supporting a transfer rate of up to 480 Mbps, compared to 12 Mbps of USB 1.1. That's about 40 times as fast! Wow!The USB trident logo