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Appendix

Basic science

Equations

1 atomic mass unit (amu) = 1/12 the mass of a carbon-12 atom

Maximum number of electrons in a shell = 2n2 (n = shell number)

Kinetic energy = ½mv2 (m = mass; v = velocity)

Frequency = 1 / T (T = time between successive peaks in seconds)

Velocity (c, ms-1) = fλ (f = frequency; λ = wavelength)

Intensity (E) = hf (h = Planck’s constant; f = frequency)

Intensity (E) = h/λ

Intensity ∝ 1 / d2 (d = distance)

Miscellaneous

 Relative massChargeSymbol
Neutron10n
Proton1+1p
Electron0 (1/2000)-1e-

1 Becquerel (Bq) = 1 transformation per second

X-ray imaging

Equations

Heat (J) = kVe x mAs = w x kVp x mAs (kVe = effective kV, w = waveform, kVp = peak kV, mAs = current per second)

Temperature rise = energy applied / heat capacity

Compton scatter ∝ density / energy

Photoelectric LAC ∝ ρZ3 / E3 (ρ = density, Z = atomic number, E = energy)

Compton LAC = ρ / E

Factor of reduction = 2HVL (HVL = half value layer)

Linear attenuation coefficient (LAC, cm-1) = 0.693 / HVL

Mass attenuation coefficient (MAC, cm2g-1) = LAC / density

Computed radiography

Image plate (IP) = barium fluorohalide activated with divalent europium ions. 0.3 mm

Red laser beam for read out

Light released in blue part of spectrum

Speed = 2000 / X (X = dose incident on IP)

Detective quantum efficiency (DQE) = SNR2out / SNR2in (SNR = signal to noise ratio)

  • 0.25 for standard IP
  • 0.12 for high resolution IP

Digital radiography

Indirect DR

Scintillator layer = 500 μm layer of caesium iodide with thallium (CsI:Tl)

X-ray photon → ~3000 light photons in green spectrum

Matrix = amorphous silicon layer doped with hydrogen (a-Si:H)

Fill factor = sensitive area / overall area

Direct DR

Photoconductor = amorphous selenium (a-Se)

Mammography

Maximum compression = 200 N (normal = 100-150 N)

Target/filter:

  • General use: MoMo
  • Dense breasts: MoRh or RhRh

Broad focal spot = 0.3 mm

Fine focal spot = 0.1 – 0.15 mm

Focus-to-film distance = 65-66 cm

Fluoroscopy

Equipment

II window made of aluminium of titanium foil

Input phosphor:

  • Sodium activated caesium iodide (CsI:Na)
  • 400-500 μm thick,
  • Produces light photons in blue spectrum

Photocathode:

  • Antimony caesium (SbCs3)

Output screen:

  • Silver-activated zinc cadmium sulphide (ZnCdS:Ag)
  • 25-35 in diameter, few micrometres thick
Equations:

Gbrightness = Gminification x Gflux (Gminification = minification gain; Gflux = flux gain)

Gminification = (Dinput / Doutput)2 (Dinput = diameter of input screen; Doutput = diameter of output screen)

Gx = L / X’ (Gx = image intensifier conversion factor; L = luminance of the output; X’ = entrance dose rate)

Gminification ~ 100

Gflux ~ 100

Gx ~ 10-30

Elements

Tungsten (W)

Characteristic radiation:

  • Kα = 59.3 keV
  • Kβ = 67.6 keV

Mass number (A) = 184

Atomic number (Z) = 74

Molybdenum (Mo)

Characteristic radiation:

  • Kα = 17.5 keV
  • Kβ = 19.6 keV

K-edge = 20 keV

Rhodium (Rh)

Characteristic radiation:

  • Kα = 20.2 keV
  • Kβ = 22.7 keV

K-edge = 23.3 keV

Image quality

Subject contrast (c) ∝ (μ1 – μ2) x t (μ = attenuation coefficient of object 1 and 2, t = object thickness)

Noise inversely proportional to √photons

Geometric unsharpness (Ug) = f x b / a (f = x-ray focal size; a = distance from x-ray source to front surface of object; b = distance from object to detector)

Magnification (M) = image size / object size = d2 / d1 (d2 = focal spot to detector; d1 = focal spot to object)

Sampling frequency = 2 x Nyquist frequency

Quality assurance

Required by IRR 1999. IPEM report 91 provides guidance.

Equipment testedFrequency of testingMethod of testingPerformance criteria
X-ray tube output1-2 monthsDose at various exposures measured with ionisation chamber at known distance

Repeatability:

  • Remedial = ± 10%
  • Suspension = ± 20%

Consistency:

  • Remedial = ± 20%
  • Suspension = ± 50%
Light beam alignment1-2 monthsLight beam field compared to exposed field on film

Remedial = 1 cm misalignment on any side at 1 m from focal spot

Suspension = 3 cm

Automatic exposure control (AEC) performance1-3 monthsFilm exposed at different tube voltages and different perspex thicknesses to ensure consistent OD

Remedial = ± 0.3 OD relative to baseline

Suspension = ± 0.5 OD relative to baseline

Low contrast sensitivity4-6 monthsUses Leeds Test Object Ltd test objectRemedial = baseline ± 2 groups
DR/CR limiting spatial resolution4-6 monthsUses lead grating resolution bar patternRemedial = baseline minus 25%
AEC ionisation chamber consistencyAnnualExpose ionisation chambers separately and compare (usually three)

Remedial = ± 0.3 OD relative to baseline

Suspension = ± 0.5 OD relative to baseline

Focal spotAnnual

Pinhole

Pinhole radiographed and size, shape and inconsistencies of focal spot calculated from image produced

Star test object

Radiating lead spokes radiographed and central blurred area size used to calculate focal spot size

 
FiltrationAnnual

Half value thickness / layer of filter determined and compared to available data to calculate filtration

Should be equivalent to 2.5 mm aluminium

 
Detector dose indicator repeatability and reproducibilityAnnual 

Remedial = baseline ± 10%

Suspension = baseline ± 20%

Threshold contrast detail detectabilityAnnualTest object with appropriate filter and kV imaged 
Uniformity of resolutionAnnualFine wire mesh imagedRemedial = increase in blurring from baseline
Scaling errorsAnnualGrid imaged with object of known lengthRemedial = >2% deviation from object
Dark noiseAnnualNo exposure or low exposureRemedial = baseline + 50%
X-ray tube kV1-2 yearsElectronic kV meter measures kV at different exposure settings

Remedial = ±5% or ±5 kV from baseline

Suspension = ± 10% or ± 5kV from baseline

CT imaging

Detector array = 8 – 64 rows; 700 – 900 detectors per row

Single slice pitch = detector pitch = couch travel per rotation / detector width

Multislice pitch = beam pitch = couch travel per rotation / total width of simultaneously acquired slices

Hounsfield unit (HU) = CT number = 1000 x (ut – uw) / uw (ut = attenuation coefficient of tissue; uw = attenuation coefficient of water)

Focal spot: fine = 0.7 mm, broad = 1.0 mm)

Pixel size (d) = FOV / n (FOV = field of view; n = image matrix size)

Highest spatial frequency (fmax) = 1 / 2d

CT number values
TissueCT number
Bone
Liver
White matter
Grey matter
Intravascular blood
Fresh clotted blood
Muscle
Kidney
CSF
Water
Fat
Air
+1000
40 to 60
20 to 30
37 to 45
40 to 45
70 to 80
10 to 40
30
15
0
-50 to -100
-1000

Dose

Dose = mAs / pitch

MeasurementDefinitionEquationUnit
CT dose index
(CTDI)
Dose to the detector from single gantry rotation mGy
Weighted CTDI
(CTDIw)
Adjusted for spatial variation of dose⅓ CTDIcentre + ⅔ CTDIperipherymGy
Volume CTDI
(CTDIvol)
Accounts for pitchCTDIw / pitchmGy
Dose length product
(DLP)
Total dose along distance scannedCTDIvol x distance scannedmGy cm
Effective dose
(E)
Physical effect of total radiation dose

1) Σ (HT x WT)

2) EDLP x DLP

HT = individual organ dose
WT = tissue weighting factor
EDLP = agreed value of EDLP for whole region

 

Ultrasound imaging

Equations

Audible range of soundwaves = 20 to 20,000 Hz

Medical ultrasound = 2 to 18 MHz

Velocity (c) = √ ƙ / ρ (ƙ = rigidity; ρ = density)

c = f λ (f = frequency; λ = wavelength)

Speed of sound through tissue = 1540 ms

Intensity (dB ratio) = 10 log10 (I1 / I2) (I1 = intensity 1; I2 = intensity 2)

Acoustic impedence (Z, kg m-2 s-1) = density x speed of sound in that material

Reflection coefficient (R) = Z2 – Z1)2 / Z2 + Z1)2

Beam weight = focal length x λ / D (λ = wavelength; D = diameter of PZT crystals)

Doppler

Resistive index (RI) = (peak systolic frequency – end diastolic frequency) ÷ peak systolic frequency

Pulsatility index (PI) = (peak systolic frequency – minimum frequency) ÷ time averaged maximum frequency

In low resistance artery: normal RI = 0.6 – 0.7; abnormal RI = 0.8 – 1.0

Nyquist limit = PRF / 2

Equipment

Piezoelectric material = ½ wavelength thick; 256 crystals

Matching layer = ¼ wavelength thick

Near field distance = D2 / 4λ (D = diameter of transducer; λ = wavelength)

Pulse repetition frequency (PRF) = frame rate x lines per frame

Distance of wave = time x velocity x 0.5

Depth of view = 0.5 x sound velocity / PRF

Safety

Thermal index (TI) = power emitted / that required to increase temperature by 1°c. Keep < 0.5

Mechanical index (MI) = peak negative pressure / √ultrasound frequency. Keep < 0.7. In fetal scanning <0.5

Time averaged intensity < 100 mWcm-2

Total sound energy < 50 Jcm-2

MR imaging

Equations

Larmor equation (F) = precessional frequency = K x B0 (K = gyromagnetic ration; B0 = strength of static magnetic field)

Larmor frequency of hydrogen at 1 Tesla = 42 MHz

Larmor frequency of hydrogen at 1.5 Tesla = 63 MHz

T1 = time for Mz (longitudinal magnetisation) to recover to 63%

T2 = time for Mxy (transverse magnetisation) to decay to 37%

Relaxation times at 1 Tesla
 T1 (ms)T2 (ms)
Fat25080
Kidney55060
White matter65090
Grey matter800100
CSF2000150
Water30003000
Bone, teethVery longVery short

Sequence

Spin echo
  • 90º RF → 180º RF rephasing pulse at TE/2 → Echo signal at time TE → repeat at TR
  • Scan time = TR x no. GPE x NEX (GPE = phase encoding steps; NEX = number of signal averages or slices)
  • Turbo spin echo = TR x no. GPE x NEX / ETL (ETL = echo train length)
  • T1 weighted: TR determines T1 signal. Short TR
  • T2 weighted: TE determines T2 signal. Long TE
  • Proton density: minimise T1 with long TR and minimise T2 with short TE
Inversion recovery
  • STIR: short TI of 130 ms (TI = time to application of 180º inversion pulse)
  • FLAIR: long TI of 2500 ms
Gradient recalled echo
  • RF pulse of certain flip angle → gradient applied to rephase spins → echo signal at time TE → repeat at TR
  • T1 weighted: large flip angle, short TE and short TR
  • T2* weighted: small flip angle, long TE and short TR
  • T2 weighted: can’t achieve
  • Proton density = small flip angle, short TE and short TR

MR Spectroscopy

  1. Suppress water signal
    • CHESS
  2. Select voxel / voxels
    • Single-voxel spectroscopy (SVS)
    • Multi-voxel chemical shift imaging
  3. Acquire spectrum
    • PRESS and STEAM
MetaboliteFrequency (ppm)RoleClinical relevance
mIMyoinositol3,6Glial marker

Raised in gliomas and MS

Reduced in herpetic encephalitis

ChoCholine3,2Cell membrane and metabolism markerRaised in tumours and demyelination
CrCreatine3,0Energy metabolism markerConstant peak
GlxGABA, glutamine, glutamate2,1 – 2,5Intracellular neuronal transmitterRaised in hepatic encephalopathy
NAAN-Acetyl-Aspartate2,0Healthy neuronal marker

Raised in Canavan’s disease

Reduced in any condition resulting in loss of neurons

LacLactate1,3 doubletAnaerobic respirationRaised in ischaemia, seizures, tumours, mitochondrial disorders
LipLipids0,9 and 1,4 Raised in necrotic tumours
aaAminoacids0,97 Raised in pyogenic abscesses

Localisation

  1. Slice select along Z-axis with gradient
  2. Segment along X-axis selected by frequency encoding
  3. Segment along Y-axis selected by phase encoding
  4. For 3D, segment along Z-axis selected by phase encoding
  5. Wave decoded with Fourier transformation

K-space: periphery for fine detail, centre for contrast information

Angiography

Time of flight (TOF): non-contrast bright blood technique. Uses flow-related enhancement artefact

Phase contrast: non-contrast bright blood technique. Uses spin phase artefact.

Contrast enhanced: IV contrast bright blood technique

Contrast agents:

  • T1 paramagnetic = shorten T1 = high T1 signal e.g. gadolinium, hepatobiliary agents that contain manganese
  • T2 superparamagnetic = speeds up T2 decay = low T2 signal e.g. iron oxide based SPIOs and USPIOs

Artefacts

Local field inhomogeneity artefacts occur in frequency-encoding direction

External RF signal artefacts occur in phase-encoding direction

Molecular imaging

Non-nuclear molecular imaging

  • Contrast-enhanced ultrasound
    • Bubbles 1-4 μm
    • Filled with high-molecular weight gas e.g. perfuorocarbon and sulphur hexafluoride
    • Shell made typically of lipid
  • Optical imaging
    • Bioluminescence: intracellular luciferase reacts with injected luciferin to produce detectable photon
    • Fluorescence: injected molecule activated with external light source and photon emissions released from decay of excited state measured
  • MR spectroscopy

Radiopharmaceuticals

  • Cyclotron: Technetium-99m (molybdenum target), Fluorine-18 (Oxygen-18 target), Gallium-67, Thallium-201
  • Nuclear reactor: Molybdenum (used to make Tc99m), Iodine-131, Xenon-133
  • Radionuclide generator: Technetium-99m, Krypton-81
Radiopharmaceutical and clinical useMethod of decayMethod of productionHalf-life

Carbon-11

C11-choline: prostate PET

C11-L-Methyl-methionine: Brain and parathyroid

PositronCyclotron20.3 m

Carbon-14

C14-Glycocholic acid: intestinal overgrowth

C14-Urea: H. pylori

BetaReactor5730 y

Chromium-51

Cr51: RBC

Cr51-EDTA: GFR

GammaReactor28 d

Cobalt-57

Co57-Cyanocobalamin: GI absorption

GammaCyclotron279 d

Fluorine-18

F18-FDG: PET

F18-sodium fluoride: bone

F18-Fluorocholine: prostate

F18-Desmothoxyfallypride: dopamine receptor

PositronCyclotron109 m

Gallium-67

Ga67-Ga3+: tumour, infection, inflammation

Ga67-Citrate: Hodgkins, inflammation

GammaCyclotron78.3

Gallium-68

Ga68-Dotatoc: neuroendocrine tumour

Ga68-PSMA: prostate

PositronGenerator68 m

Indium-111

In111-DTPA: VP shunt, cisternography

In111-leucocytes: inflammation / infection

In111-platelets: thrombus

In111-Pentetreotide or Octreotide: neuroendocrine tumour

GammaCyclotron1.81 d

Iodine-123

I123-Iodide: thyroid function and mets

I123-MIBG: neuroectodermal tumour

I123-ioflupane aka DaTscan: Parkinsons

GammaCyclotron13.2 h

Iodine-131

I131-Iodide: hyperthyroid, thyroid cancer

I131-MIBG: neuroectodermal tumour

Gamma and betaReactor8.06 d

Krypton-81m

K81m-gas: ventilation

K81m-aqueous: lung perfusion

GammaCyclotron13 s

Oxygen-15

O15-water

PositronCyclotron2.04 s

Strontium-89

Sr89-Chloride: bone mets

BetaReactor50.5 d

Technetium-99m

Tc99m-Pertechnetate: thyroid, stomach, Meckel’s, brain

Tc99m-human albumin: blood pool, lung perfusion

Tc99m-Phosphonates: bone, myocardial

Tc99m-DTPA: renal and brain

Tc99m-DTPA: lung ventilation

Tc99m-DMSA: tumour and renal

Tc99m-Colloid: bone marrow, GI bleeding

Tc99m-HIDA: biliary function

Tc99m-denature RBCs: RBC volume, spleen

Tc99m-whole RBCs: GI bleeding, cardiac blood pool

Tc99m-MAG3: renal

Tc99m-HMPOA: cerebral perfusion

Tc99m-examatazime labelled leucocytes: infection / inflammation

Tc99m-Sestamibi: myocardium, parathyroid

Tc99m-TetrofosminL parathryoid, myocardium

Tc99m-Tilmanocept: lymphatic mapping

GammaGenerator6.02 h

Thallium-201

TI201-Tl: thyroid tumour, parathyroid, myocardium

GammaCyclotron73.5 h

Xenon-133

Xe133-gas: inhalation

Xe133 in isotonic sodium chloride: cerebral perfusion

GammaReactor2.26 d

Equipment

Collimator:

  • Low energy = 150 keV = 0.3 mm = 99mTc
  • Medium energy = 300 keV = 1 mm = Indium-111
  • High energy = 400 keV = 2 mm = 131I

Scintillation crystal: sodium iodide with thallium (NaI(Tl)); 6-13 mm thick

PET imaging

Positron decay → annihilation with electron → two 511 keV photons

Scintillation crystal: bismuth germanate (BSO), lutetium oxyorthosilicate (LSO and gadolinium oxyorthosillicate (GSO)

Image quality

Subject contrast (Cs) = (AL – AT) / AT (AL = activity per unit of lesion; AT = activity per unit mass of healthy tissue)

Image contrast (CI) = (SL – ST) / ST (SL = counts per unit area of lesion; ST = counts per unit area of healthy tissue)

Noise contrast (CN) = 1 / √(AS) (A = area; S = count density)

Collimator spatial resolution (RC) ≈ d (1 + b/h) (d = hole diameter; b = distance from radiation source to collimator; h = hole length)

System spatial resolution (RS) = √(RI2 + RC2) (RI = intrinsic spatial resolution; RC = collimator spatial resolution)

Energy resolution = FWHM (keV) / photopeak energy (keV) x 100 (FWHM = full width half maximum)

Scatter rejection = 20% acceptance window

Radiation dosimetry, protection and legislation

Dose

Absorbed dose (Gray) = energy deposited per unit mass of tissue

Effective dose (Sievert) = ∑(equivalent dose x tissue weighting factor)

Equivalent dose = ∑(absorbed dose to tissue x radiation weighting factor)

Background radiation = 2.7 mSv/year (2.3 mSv natural sources, 0.4 mSv medical exposure)

RadiationRadiation weighting factor
X-ray and gamma ray1
Beta particles and positrons1
Neutrons < 10 keV5
Neutrons 100 keV – 2 MeV20
Alpha particles20

External radiation: gamma and x-rays > beta > alpha

Internal radiation: alpha > beta > gamma and x-rays

For other dose effects see: Dose effects

OrganTissue weighting factor
Skin, bone, brain, salivary glands0.01
Bladder, oesophagus, liver, thyroid0.04
Gonads0.08
Red bone marrow, colon, lung, stomach, breast, remainder of tissues0.12

Protection

ProtectionLead equivalence
Lead aprons

0.25 mm for 100 kV

0.35 mm for 150 kV

Thyroid shields0.5 mm
Lead glasses0.25 x 1.0 mm
Lead gloves0.25 mm
Modern gloves have 0.5 or 1.0 mm

Legislation

Ionising Radiation (Medical Exposure) Regulations (2017) (IR(ME)R 2017)

  • ALARP – as low as reasonably practicable
  • Governs all medical and non-medical exposures to patients

Ionising Radiation Regulations 2017 (IRR17)

  • Under Health and Safety at Work Act 1974
  • Minimises radiation exposure to employees and members of the public
  • Enforced by Health and Safety Executive (HSE)
Effective dose limits per year:
Radiation workers > 18 years old

20 mSv

100 mSv in any 5 consecutive years, max dose of 50 mSv in any single year

Members of public1 mSv
Radiation workers < 18 yo6 mSv i.e. 3/10 of adult dose
Dose limit to abdomen of person of reproductive capacity13 mSv in any consecutive 3 months
Comforters and carers5 mSv
Any other person / member of public (fetus counts as members of the public)1 mSv
Pregnant employees dose to foetus1 mSv for remainder of pregnancy
Equivalent dose limits per year:
AreaEmployees and trainees >18 yoTrainees <18 yoAny other person
Lens of the eye20 mSv15 mSv15 mSv
Extremities500 mSv150 mSv50 mSv
Skin500 mSv150 mSv50 mSv
Classified workers

Anyone who is likely to receive:

  • Effective dose of > 6 mSv in a year (3/10 of dose limit)
  • Equivalent dose of > 3/10 of any dose limit i.e.
    • >15 mSv/year to lens
    • 150 mSv/year to skin or extremities
Controlled area
  • Person likely to receive effective dose of > 6 mSv; 15 mSv to lens; or equivalent dose of >3/10 of any relevant dose limit
  • External dose rate exceeds 7.5 mSv/h over working day
  • Dose rate < 7.5 mSv/h over working day BUT instantaneous dose rate at any point exceeds 100 mSv/h
Supervised area
  • Person working in area likely to receive dose of > 1mSv/yr or equivalent dose of > 1/10 of any relevant dose limit
Diagnostic Reference Levels (DRLs)

Source: National Diagnostic Reference Levels 19 August 2019

RadiographESD per radiograph (mGy)DAP per radiograph (Gy cm 2)
Abdomen AP42.5
Chest AP0.20.15
Chest PA0.150.1
Cervical spine (AP and lat) 0.3
Knee (AP and lat)0.60.6
Lumbar spine AP5.71.5
Lumbar spine lat102.5
Pelvis AP42.2
Shoulder AP0.5 
Skull AP/PA1.8 
Skull lat1.1 
Thoracic spine AP3.51.0
Thoracic spine lat71.5
Adult CTCTDI vol per sequence (mGy)DLP per complete examination (mGy cm)
Head60970
Cervical spine21440
Chest12610
High-resolution CT chest4140
Chest, abdomen and pelvis 1000
CT abdominal angiography151040
CTPA13440
Abdomen14910
Abdomen and pelvis15745
Virtual colonoscopy11950
Kidneys, ureter and bladder10460
Urogram 170
Coronary CT angiography 170 – 380
Paediatric CTCTD vol per sequence (mGy)DLP per complete examination (mGy cm)
Paeds head: 0-1 y25350
Paeds head: >1-5 y40650
Paeds head: <5 y60860
Adult CT-PET / CT-SPECTCTDI vol per sequence (mGy)DLP per complete examination (mGy cm)
PET half body4.3400
SPECT bone scan4.9150
SPECT parathryoid5.6170
SPECT mIBG / octreotide5.5240
SPECT cardiac2136
Reporting overexposure:
Accidental exposure 
Exposure categoryCriteria for notification
All modalities including therapy

< 3 mSv effective dose (adult)

< 1 mSv effective dose (child)

Unintended exposure 
Exposure categoryCriteria for notification
Intended dose < 0.3 mSv

< 3 mSv (adult)

< 1 mSv (child)

Intended dose 0.3 to 2.5 mSv< 10x more than intended
Intended dose 2.5 to 10 mSv< 25 mSv
Intended dose > 10 mSv< 2.5x more than intended
Interventional / cardiologyNo procedural failure AND either: dose ≥ 10x local DRL OR observable deterministic effects excluding transient erythema
Radiotherapy pre-treatment planning scansCT planning scan needs to be repeated twice to obtain appropriate data set (i.e. 3 scans in total including the intended scan)
Foetal – all modalitiesFailure in the procedure for making pregnancy enquiries AND resultant foetal dose ≥ 1 mGy
Breast feeding infant – nuclear medicine onlyFailure in procedure AND resultant infant effect dose ≥ 1 mSv

Nuclear medicine

MARS78: governs administration of radioactive substance

RSA93: governs storage and safe disposal of radioactive materials

Radioactive Material (Road Transport) (Great Britain) Regulation 2001: governs transport of radioactive substances by road

MRI safety

MHRA guideline for whole body exposure of patients

  • Normal and pregnant 4 Tesla
  • Controlled 8 Tesla
  • Research no limit Tesla

MHRA guideline for exposure of staff

  • < 2 T for whole body
  • < 5 T for limbs
  • < 0.2 T over 24 hours

Controlled area = 5 Gauss, 0.5 mT boundary

1 SAR = 1 W/kg = whole body temperature rise of 0.5ºc

  Localised temperature limits (°c) 
Operating modeRise of body core temperature (°c)HeadTrunkExtremitiesSAR W/Kg
Normal0.53839402
Controlled13839404
Restricted2394041> 4

Hearing protection needed at 90 dB

Miscellaneous

Resolution

Imaging modalityResolution
Film screen radiograph6 lp/mm
Digital radiograph3 lp/mm
Film screen mammography15 lp/mm
Digital mammography5 to 10 lp/mm
Fluoroscopy1 lp/mm
Direct subtraction angiography2 lp/mm
Fluoroscopy – flat panel detector3 lp/mm
CT: transaxial2 lp/mm
CT: Z-sensitivity2 to 0.4 lp/mm

Effective radiation dose

ProcedureDoseProcedureDose (mSv)
Abdominal
CT Abdo/pelvis10XR lower GIT3
CT colonography6XR upper GIT6
Barium enema7XR pelvis0.5
CNS
CT head2XR cervical spine0.2
CT spine6XR thoracic spine1.0
CT neck3XR lumbar spine1.5
  XR skull< 0.1
Chest
CT chest7XR chest0.1
Cardiac CT3Mammography0.4
Cardiac CTA12 – 20  
Extremities
  XR hand / foot0.005
Nuclear imaging
Brain PET (18F FDG)14DEXA0.001
Brain perfusion (99mTc HMPAO)9 to 10Renal MAG32
Brain SPECT (99mTc sestamibi)10Renal DTPA2
Bone scan6DaTscan brain6 to 10
Heart stress (99mTc sestamibi)9.4V/Q2.5
Thyroid scan5Gastric emptying1
Whole PET/CT24  
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