Methods that infer internal biological structure or function from measured signals. Computed tomography, positron emission tomography and single-photon emission computed tomography use different signal-generation and reconstruction physics.
Pelvic ultrasonography uses ultrasonography to image structures in the pelvis, including the reproductive organs and urinary bladder. The probe's position determines the acoustic path and which structures lie in view: transabdominal and transvaginal ultrasound approaches observe the region from different geometries. Returning echoes provide information about interfaces and motion, with the usual limitations of acoustic access through gas and bone.[ref]
Pelvis Ultrasound by RadiologyInfo.org. What is Pelvic Ultrasound Imaging? and How does the procedure work?
Endoscopic ultrasonography combines an endoscope with an acoustic transducer to obtain ultrasonography images from within the gastrointestinal tract. Positioning the source and receiver near a target shortens the intervening acoustic path and can reveal the wall and nearby structures. A probe integrated into the endoscope tip and a probe passed through its working channel are different apparatus arrangements.[ref]
Guidelines for credentialing and granting privileges for endoscopic ultrasound by American Society for Gastrointestinal Endoscopy. Definition of terms: EUS, echoendoscope and catheter ultrasound probe
Magnetic resonance cholangiopancreatography is a form of magnetic resonance imaging used to visualize the bile ducts and pancreatic duct. Its apparatus uses a magnetic field, radiofrequency excitation and spatially encoded magnetic-resonance signals to produce images of the ductal region. The image depends on the selected acquisition and reconstruction, so visible duct structure is an inference from that signal rather than a direct optical view.[ref]
MRCP (MR Cholangiopancreatography) by RadiologyInfo.org. What is MRCP?: magnetic resonance imaging and the hepatobiliary and pancreatic systems
Transillumination examines internal structure using light transmitted through a body region or specimen. The source illuminates one side and the observer or detector records light emerging after propagation through the material. Different optical absorption and scattering properties can create image contrast.[ref]
Transillumination in the MeSH thesaurus by National Library of Medicine. descriptor D014172: passage of light through tissues or cavities to examine internal structure
A simple physical demonstration illuminates a fingertip from behind and observes the diffuse transmitted glow. Its appearance depends on wavelength, path length and the tissue's optical properties. Strong scattering redistributes the paths, so a brightness difference cannot generally be interpreted as a sharply localized anatomical boundary without an additional model.
Ultrasonography forms medical images using ultrasound. In pulse-echo imaging, a piezoelectric transducer emits a short acoustic pulse and receives echoes from changes in acoustic impedance. If an echo returns after time from a reflector at distance in a uniform medium with sound speed , the round trip gives . Scanning the beam assembles spatial information from many such measurements.[ref]
Ultrasound by National Institute of Biomedical Imaging and Bioengineering. How does it work?: piezoelectric emission and reception, echo timing and acoustic coupling
A water-tank experiment with two reflectors at known separations tests the depth calculation without biological interpretation. An incorrect assumed sound speed changes the inferred depths; overlapping pulses limit the separation of nearby reflectors. In tissue, acoustic attenuation, scattering and the geometry of the beam further affect the image. These mechanisms explain why the displayed anatomy depends on both physical propagation and the acquisition model.
Pulse-echo imaging sends a short acoustic pulse and records echoes returning from interfaces or scatterers. If sound speed is approximately constant and the path is straight, an echo delay corresponds to range , because sound travels to the scatterer and back.
Scanning beam direction and measuring echo strength produces an image. Pulse duration and bandwidth affect axial resolution, while beam width affects transverse resolution. Incorrect sound-speed assumptions distort inferred positions, and multiple reflections can create echoes that do not correspond to a single direct round trip.
Use of ultrasonography to examine the urinary bladder, including assessment of its distension in suspected urinary retention.
Transvaginal ultrasound is pelvic ultrasonography with an internal probe positioned in the vagina, close to pelvic structures such as the uterus and ovaries. This changes the imaging geometry and the intervening acoustic path. The measured signal is still an ultrasound echo; the probe's position supplies access to structures that can be harder to view along an external abdominal path.[ref]
Pelvis Ultrasound by RadiologyInfo.org. Transvaginal and What are some common uses?: internal probe and pelvic targets
Doppler ultrasonography applies Doppler ultrasound to motion within the body, especially flowing blood. Moving scatterers change the returned frequency or phase; the shift measures a component of velocity along the acoustic geometry. Combining that information with ultrasonography locates motion relative to the imaged structures.[ref]
Venous Ultrasound by RadiologyInfo.org. What is Venous Ultrasound Imaging?: Doppler measurement of moving materials and blood flow
A color map assigns a display color to a measured flow quantity under a chosen sign convention. It therefore represents an inferred motion, rather than the literal optical color of the blood. Estimating a speed requires the beam-to-flow angle and the assumptions behind the Doppler ultrasound measurement; a small shift can reflect a nearly transverse flow as well as a small speed.
Compression ultrasonography combines ultrasonography with observation of how a structure deforms under an applied load. For a vein, the image records whether the opposing walls approach each other during compression. A segment that fails to compress can provide evidence of an obstructing thrombus; the useful measurement is the dynamic mechanical response as well as its visual appearance.[ref]
Emergency Ultrasound Imaging Criteria Compendium by American College of Emergency Physicians. venous ultrasound: compression, documentation of complete/partial/absent compressibility and limitations
Interpretation depends on adequate visualization and loading: an incomplete view or ineffective compression does not establish the same physical observation as a properly imaged noncompressible segment. This illustrates a general measurement principle: the input perturbation and the object's response both belong to the experiment.
Compensation for photons lost along an emission-imaging path. In PET/CT or SPECT/CT, a registered computed tomography attenuation map supplies information for this correction.
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Medical imaging is a technique used in healthcare to create visual representations of the interior of a body for clinical analysis and medical intervention. It plays a crucial role in diagnosing, monitoring, and treating various medical conditions. Different medical imaging modalities provide unique insights and benefits, and they can be used independently or in conjunction to obtain comprehensive information about a patient's health.