Anisotropy
Citation, DOI & article data
Anisotropy is an artifact encountered in ultrasound, notably in muscles and tendons during a musculoskeletal ultrasound. In musculoskeletal applications, the artifact may prompt an incorrect diagnosis of tendinosis or tendon tear.
When the ultrasound beam is incident on a fibrillar structure such as a tendon or a ligament, the organized fibrils may reflect a majority of the insonating sound beam in a direction away from the transducer. When this occurs, the transducer does not receive the returning echo and assumes that the insonated area should be hypoechoic.
This anisotropic effect is dependent on the angle of the insonating beam. The maximum return echo occurs when the ultrasound beam is perpendicular to the tendon. Decreasing the insonating angle on a normal tendon will cause it to change from brightly hyperechoic (the actual echo from tightly bound tendon fibers) to darkly hypoechoic. If the angle is then increased, the tendon will again appear hyperechoic.
If the artifact causes a normal tendon to appear hypoechoic, it may falsely lead to a diagnosis of tendinosis or tear.
In some situations, anisotropy may be useful in diagnosis. If a tendon is surrounded by other brightly hyperechoic structures (e.g. fat), then altering the angle of the transducer will cause the tendon to become hypoechoic, differentiating it from the other structures.
See also
References
- 1. Lin DC, Nazarian LN, O'Kane PL et-al. Advantages of real-time spatial compound sonography of the musculoskeletal system versus conventional sonography. AJR Am J Roentgenol. 2002;179 (6): 1629-31. doi:10.2214/ajr.179.6.1791629 - Pubmed citation
Related articles: Imaging technology
- imaging technology
- imaging physics
- imaging in practice
-
x-rays
- x-ray physics
- x-ray in practice
- x-ray production
- x-ray tube
- filters
- automatic exposure control (AEC)
- beam collimators
- grids
- air gap technique
- cassette
- intensifying screen
- x-ray film
- image intensifier
- digital radiography
- digital image
- mammography
- x-ray artifacts
- radiation units
- radiation safety
- radiation detectors
- fluoroscopy
-
computed tomography (CT)
- CT physics
- CT in practice
- CT technology
- CT image reconstruction
- CT image quality
- CT dose
-
CT contrast media
-
iodinated contrast media
- agents
- water soluble
- water insoluble
- vicarious contrast material excretion
- iodinated contrast media adverse reactions
- agents
- non-iodinated contrast media
-
iodinated contrast media
-
CT artifacts
- patient-based artifacts
- physics-based artifacts
- hardware-based artifacts
- ring artifact
- tube arcing
- out of field artifact
- air bubble artifact
- helical and multichannel artifacts
- CT safety
- history of CT
-
MRI
- MRI physics
- MRI in practice
- MRI hardware
- signal processing
-
MRI pulse sequences (basics | abbreviations | parameters)
- T1 weighted image
- T2 weighted image
- proton density weighted image
- chemical exchange saturation transfer
- CSF flow studies
- diffusion weighted imaging (DWI)
- echo-planar pulse sequences
- fat-suppressed imaging sequences
- gradient echo sequences
- inversion recovery sequences
- metal artifact reduction sequence (MARS)
-
perfusion-weighted imaging
- techniques
- derived values
- saturation recovery sequences
- spin echo sequences
- spiral pulse sequences
- susceptibility-weighted imaging (SWI)
- T1 rho
- MR angiography (and venography)
-
MR spectroscopy (MRS)
- 2-hydroxyglutarate peak: resonates at 2.25 ppm
- alanine peak: resonates at 1.48 ppm
- choline peak: resonates at 3.2 ppm
- citrate peak: resonates at 2.6 ppm
- creatine peak: resonates at 3.0 ppm
- functional MRI (fMRI)
- gamma-aminobutyric acid (GABA) peak: resonates at 2.2-2.4 ppm
- glutamine-glutamate peak: resonates at 2.2-2.4 ppm
- Hunter's angle
- lactate peak: resonates at 1.3 ppm
- lipids peak: resonates at 1.3 ppm
- myoinositol peak: resonates at 3.5 ppm
- MR fingerprinting
- N-acetylaspartate (NAA) peak: resonates at 2.0 ppm
- propylene glycol peak: resonates at 1.13 ppm
-
MRI artifacts
- MRI hardware and room shielding
- MRI software
- patient and physiologic motion
- tissue heterogeneity and foreign bodies
- Fourier transform and Nyquist sampling theorem
- MRI contrast agents
- MRI safety
-
ultrasound
- ultrasound physics
-
transducers
- linear array
- convex array
- phased array
- frame averaging (frame persistence)
- ultrasound image resolution
- imaging modes and display
- pulse-echo imaging
- real-time imaging
-
Doppler imaging
- Doppler effect
- color Doppler
- power Doppler
- B flow
- color box
- Doppler angle
- pulse repetition frequency and scale
- wall filter
- color write priority
- packet size (dwell time)
- peak systolic velocity
- end-diastolic velocity
- resistive index
- pulsatility index
- Reynolds number
- panoramic imaging
- compound imaging
- harmonic imaging
- elastography
- scanning modes
- 2D ultrasound
- 3D ultrasound
- 4D ultrasound
- M-mode
-
ultrasound artifacts
- acoustic shadowing
- acoustic enhancement
- beam width artifact
- reverberation artifact
- ring down artifact
- mirror image artifact
- side lobe artifact
- speckle artifact
- speed displacement artifact
- refraction artifact
- multipath artifact
- anisotropy
- electrical interference artifact
- hardware-related artifacts
- Doppler artifacts
- aliasing
- tissue vibration
- spectral broadening
- blooming
- motion (flash) artifact
- twinkling artifact
- acoustic streaming
- biological effects of ultrasound
- history of ultrasound
-
nuclear medicine
- nuclear medicine physics
- detectors
- tissue to background ratio
-
radiopharmaceuticals
- fundamentals of radiopharmaceuticals
- radiopharmaceutical labeling
- radiopharmaceutical production
- nuclear reactor produced radionuclides
- cyclotron produced radionuclides
- radiation detection
- dosimetry
- specific agents
- carbon-11
- chromium-51
- fluorine agents
- gallium agents
- Ga-67 citrate
- Ga-68
- iodine agents
-
I-123
- I-123 iodide
- I-123 ioflupane (DaTSCAN)
- I-123 ortho-iodohippurate
- I-131
-
MIBG scans
- I-123 MIBG
- I-131 MIBG
-
I-123
- indium agents
- In-111 Octreoscan
- In-111 OncoScint
- In-111 Prostascint
- In-111 oxine labeled WBC
- krypton-81m
- nitrogen-13
- oxygen-15
- phosphorus-32
- selenium-75
-
technetium agents
- Tc-99m DMSA
- Tc-99m DTPA
- Tc-99m DTPA aerosol
- Tc-99m HMPAO
- Tc-99m HMPAO labeled WBC
- Tc-99m MAA
- Tc-99m MAG3
- Tc-99m MDP
- Tc-99m mercaptoacetyltriglycine
- Tc-99m pertechnetate
- Tc-99m labeled RBC
- Tc-99m sestamibi
- Tc-99m sulfur colloid
- Tc-99m sulfur colloid (oral)
- thallium-201 chloride
- xenon agents
- in vivo therapeutic agents
- pharmaceuticals used in nuclear medicine
-
emerging methods in medical imaging
- radiography
- phase-contrast imaging
- CT
- deep-learning reconstruction
- photon counting CT
- virtual non-contrast imaging
- ultrasound
- magnetomotive ultrasound (MMUS)
- superb microvascular imaging
- ultrafast Doppler imaging
- ultrasound localization microscopy
- MRI
- nuclear medicine
- total body PET system
- immuno-PET
- miscellaneous
- radiography
Related articles: Ultrasound - musculoskeletal
- ultrasound (introduction)
-
musculoskeletal ultrasound
- shoulder ultrasound
- elbow ultrasound
- wrist ultrasound
- hand ultrasound
- hip ultrasound
-
knee ultrasound
- Baker cyst (popliteal cyst)
- infrapatellar bursitis
- ankle/foot ultrasound
- pediatric musculoskeletal ultrasound
- other
- skin/soft tissue ultrasound
- lipoma
- parasitic infection
- ultrasound of arthropathies
- technique/artifacts