Photocathode
Last revised by Andrew Murphy on 29 Mar 2020
Citation, DOI, disclosures and article data
Citation:
MacManus D, Murphy A, Bell D, et al. Photocathode. Reference article, Radiopaedia.org (Accessed on 03 Oct 2024) https://doi.org/10.53347/rID-74263
Permalink:
rID:
74263
Article created:
13 Feb 2020,
Daniel MacManus
Disclosures:
At the time the article was created Daniel MacManus had no recorded disclosures.
View Daniel MacManus's current disclosures
Last revised:
29 Mar 2020,
Andrew Murphy ◉
Disclosures:
At the time the article was last revised Andrew Murphy had no recorded disclosures.
View Andrew Murphy's current disclosures
Revisions:
5 times, by
4 contributors -
see full revision history and disclosures
Sections:
Synonyms:
- Photocathodes
A photocathode is a negatively charged electrode in a light detection device such as the input screen in an image intensifier (II) that is coated with a photosensitive compound. When this is struck by light photons, the absorbed energy causes electron emission due to the photoelectric (PE) effect.
Composition
In an image intensifier, the photocathode is a thin layer of an alloy of antimony and cesium (SbCs3). The photocathode converts the light photons emitted by the entrance phosphor to photoelectrons via the PE effect:
- electrons are produced in direct proportion to the brightness of the input screen
- 10-20% conversion efficiency, i.e. approx. 400 electrons are released from the photocathode for each 60 keV x-ray photon absorbed by the phosphor
In order to preserve the image faithfully, the input phosphor and photocathode must be in intimate contact with each other, separated only by a thin transparent wafer which prevents chemical interaction between the two layers.
The light spectrum of the input phosphor should also match the sensitivity profile of the photocathode, to maximize the conversion efficiency from light photons to photoelectrons.
References
- 1. Bushberg JT, Siebert JA, Leidholdt EM & Boone JM. The Essential Physics of Medical Imaging, Lippincott, Williams & Wilkins, 3rd Edition (2011). p233
Incoming Links
Articles:
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
Unable to process the form. Check for errors and try again.