Flow void
Citation, DOI, disclosures and article data
At the time the article was created Bruno Di Muzio had no recorded disclosures.
View Bruno Di Muzio's current disclosuresAt the time the article was last revised Arlene Campos had no financial relationships to ineligible companies to disclose.
View Arlene Campos's current disclosures- Flow voids
Flow voids is a term used when describing MRI studies and refers to signal loss occurring within moving fluids (usually blood but also frequently seen in CSF or urine) when the fluid is moving at a sufficient velocity relative to the MRI apparatus. Some MRI sequences are more susceptible to flow-induced signal voids than others as it is a combination of time-of-flight and spin-phase effects and thus usually seen in spin-echo techniques (such as T2-weighted images) 2.
Flow voids are a form of MRI artifact. Often they are useful as they allow patency and flow to be inferred. Sometimes, however, they can be mistaken for pathology.
Physics
During spin-echo imaging, protons in flowing fluid move out of the plane of spatially-selective radiofrequency pulses, in the time between the initial 90° excitation pulse and the second 180° refocusing pulse. Because of this time-of-flight effect, these protons miss the refocusing pulse and dephase, thereby contributing no signal to that voxel 1-3. (A different time-of-flight phenomenon occurs in flow-compensated gradient-echo sequences resulting in flow-related enhancement, harnessed in time-of-flight angiography.) The degree of signal loss due to this time-of-flight effect is related to the velocity of the proton out of the plane, the slice thickness, and the time to echo (TE) 1.
Spin-phase effects account for signal loss occurring with motion within the same plane of imaging. The velocity of blood varies at different points across the lumen of a vessel, whether during laminar or turbulent flow. Protons moving at different velocities then gain different phases as they move across the gradient applied for spatial encoding. The phase shift depends on the velocity of the proton within the plane, strength of the applied gradient, and time to echo. As these differences occur on a microscopic level, spin dephasing causes signal loss within a voxel.
Practical points
flow void is synonymous with vascular patency, representing a normal flow-related signal loss in vessels that contain vigorously flowing blood
sequences with long TE (such as T2 and PD) have most prominent flow voids; when vascular thrombosis is identified on a T1-weighted sequence (short TE), it should be confirmed by the corresponding T2 or PD sequences, as these are less sensitive to slow flow voids and more specific to the diagnosis of thrombosis
flow voids can also been seen along transverse T2-weighted images of the spine, as the CSF flows perpendicular to slice direction 2
aqueduct stenosis is a pathologic condition in which CSF flow voids are not present
Quiz questions
References
- 1. Wells Mangrum, MD, Kimball Christianson, MD, Scott M Duncan, MD et al. Duke Review of MRI Principles: Case Review Series. (2012) ISBN: 9781455700844 - Google Books
- 2. Marinus T. Vlaardingerbroek, Jacques A. Boer. Magnetic Resonance Imaging. (2003) ISBN: 9783540436812 - Google Books
- 3. Gunderman R. Essential Radiology: Clinical Presentation · Pathophysiology · Imaging. TNY. ISBN:B005WJJM26. Read it at Google Books - Find it at Amazon
Incoming Links
- MR vessel wall imaging
- Cerebral microhaemorrhage
- Pineal and tectal plate protocol (MRI)
- Infantile hepatic haemangioma
- Enhanced myometrial vascularity
- Deep cerebral vein thrombosis
- Intramuscular haemangiomas
- Sarcoma with BCOR genetic alteration
- Dural venous sinus thrombosis
- Angiomatous meningioma
- Juvenile nasopharyngeal angiofibroma
- Portal venous varix
- Spinal arteriovenous fistula
- Spinal arteriovenous malformations
- Vein of Galen aneurysmal malformation
- Aqueduct stenosis
- Haemangioblastoma (central nervous system)
- Choledocholithiasis
- Brain tumour protocol (MRI)
- Cerebral arteriovenous malformation
- Collet-Sicard syndrome due to jugular paraganglioma
- Rapidly involuting congenital hemangioma (RICH) - prenatally discovered
- Intramuscular hemangioma - child
- Intramuscular haemangioma - suboccipital neck
- Temporal subcutaneous high-flow arteriovenous malformation
- Lymphatic malformation
- Central neurocytoma
- Haemorrhagic venous infarction
- Anterior (ventral) cord herniation
- Diffuse leptomeningeal glioneuronal tumor
- Cerebral arteriovenous malformation
- Japanese encephalitis
- Transverse venous sinus aneurysm
- MRI artifact (flow void between urinary bladder and bladder diverticulum)
- Ventral cord herniation
- Haemangioblastoma of the thoracic spine
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