Contents
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 mass | Charge | Symbol | |
| Neutron | 1 | 0 | n |
| Proton | 1 | +1 | p |
| Electron | 0 (1/2000) | -1 | e- |
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 tested | Frequency of testing | Method of testing | Performance criteria |
|---|---|---|---|
| X-ray tube output | 1-2 months | Dose at various exposures measured with ionisation chamber at known distance | Repeatability:
Consistency:
|
| Light beam alignment | 1-2 months | Light 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) performance | 1-3 months | Film 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 sensitivity | 4-6 months | Uses Leeds Test Object Ltd test object | Remedial = baseline ± 2 groups |
| DR/CR limiting spatial resolution | 4-6 months | Uses lead grating resolution bar pattern | Remedial = baseline minus 25% |
| AEC ionisation chamber consistency | Annual | Expose ionisation chambers separately and compare (usually three) | Remedial = ± 0.3 OD relative to baseline Suspension = ± 0.5 OD relative to baseline |
| Focal spot | Annual | 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 | |
| Filtration | Annual | 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 reproducibility | Annual | Remedial = baseline ± 10% Suspension = baseline ± 20% | |
| Threshold contrast detail detectability | Annual | Test object with appropriate filter and kV imaged | |
| Uniformity of resolution | Annual | Fine wire mesh imaged | Remedial = increase in blurring from baseline |
| Scaling errors | Annual | Grid imaged with object of known length | Remedial = >2% deviation from object |
| Dark noise | Annual | No exposure or low exposure | Remedial = baseline + 50% |
| X-ray tube kV | 1-2 years | Electronic 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
| Tissue | CT 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
| Measurement | Definition | Equation | Unit |
|---|---|---|---|
| CT dose index (CTDI) | Dose to the detector from single gantry rotation | mGy | |
| Weighted CTDI (CTDIw) | Adjusted for spatial variation of dose | ⅓ CTDIcentre + ⅔ CTDIperiphery | mGy |
| Volume CTDI (CTDIvol) | Accounts for pitch | CTDIw / pitch | mGy |
| Dose length product (DLP) | Total dose along distance scanned | CTDIvol x distance scanned | mGy cm |
| Effective dose (E) | Physical effect of total radiation dose | 1) Σ (HT x WT) 2) EDLP x DLP HT = individual organ dose |
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) | |
|---|---|---|
| Fat | 250 | 80 |
| Kidney | 550 | 60 |
| White matter | 650 | 90 |
| Grey matter | 800 | 100 |
| CSF | 2000 | 150 |
| Water | 3000 | 3000 |
| Bone, teeth | Very long | Very 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
- Suppress water signal
- CHESS
- Select voxel / voxels
- Single-voxel spectroscopy (SVS)
- Multi-voxel chemical shift imaging
- Acquire spectrum
- PRESS and STEAM
| Metabolite | Frequency (ppm) | Role | Clinical relevance | |
|---|---|---|---|---|
| mI | Myoinositol | 3,6 | Glial marker | Raised in gliomas and MS Reduced in herpetic encephalitis |
| Cho | Choline | 3,2 | Cell membrane and metabolism marker | Raised in tumours and demyelination |
| Cr | Creatine | 3,0 | Energy metabolism marker | Constant peak |
| Glx | GABA, glutamine, glutamate | 2,1 – 2,5 | Intracellular neuronal transmitter | Raised in hepatic encephalopathy |
| NAA | N-Acetyl-Aspartate | 2,0 | Healthy neuronal marker | Raised in Canavan’s disease Reduced in any condition resulting in loss of neurons |
| Lac | Lactate | 1,3 doublet | Anaerobic respiration | Raised in ischaemia, seizures, tumours, mitochondrial disorders |
| Lip | Lipids | 0,9 and 1,4 | Raised in necrotic tumours | |
| aa | Aminoacids | 0,97 | Raised in pyogenic abscesses | |
Localisation
- Slice select along Z-axis with gradient
- Segment along X-axis selected by frequency encoding
- Segment along Y-axis selected by phase encoding
- For 3D, segment along Z-axis selected by phase encoding
- 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 use | Method of decay | Method of production | Half-life |
|---|---|---|---|
Carbon-11 C11-choline: prostate PET C11-L-Methyl-methionine: Brain and parathyroid | Positron | Cyclotron | 20.3 m |
Carbon-14 C14-Glycocholic acid: intestinal overgrowth C14-Urea: H. pylori | Beta | Reactor | 5730 y |
Chromium-51 Cr51: RBC Cr51-EDTA: GFR | Gamma | Reactor | 28 d |
Cobalt-57 Co57-Cyanocobalamin: GI absorption | Gamma | Cyclotron | 279 d |
Fluorine-18 F18-FDG: PET F18-sodium fluoride: bone F18-Fluorocholine: prostate F18-Desmothoxyfallypride: dopamine receptor | Positron | Cyclotron | 109 m |
Gallium-67 Ga67-Ga3+: tumour, infection, inflammation Ga67-Citrate: Hodgkins, inflammation | Gamma | Cyclotron | 78.3 |
Gallium-68 Ga68-Dotatoc: neuroendocrine tumour Ga68-PSMA: prostate | Positron | Generator | 68 m |
Indium-111 In111-DTPA: VP shunt, cisternography In111-leucocytes: inflammation / infection In111-platelets: thrombus In111-Pentetreotide or Octreotide: neuroendocrine tumour | Gamma | Cyclotron | 1.81 d |
Iodine-123 I123-Iodide: thyroid function and mets I123-MIBG: neuroectodermal tumour I123-ioflupane aka DaTscan: Parkinsons | Gamma | Cyclotron | 13.2 h |
Iodine-131 I131-Iodide: hyperthyroid, thyroid cancer I131-MIBG: neuroectodermal tumour | Gamma and beta | Reactor | 8.06 d |
Krypton-81m K81m-gas: ventilation K81m-aqueous: lung perfusion | Gamma | Cyclotron | 13 s |
Oxygen-15 O15-water | Positron | Cyclotron | 2.04 s |
Strontium-89 Sr89-Chloride: bone mets | Beta | Reactor | 50.5 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 | Gamma | Generator | 6.02 h |
Thallium-201 TI201-Tl: thyroid tumour, parathyroid, myocardium | Gamma | Cyclotron | 73.5 h |
Xenon-133 Xe133-gas: inhalation Xe133 in isotonic sodium chloride: cerebral perfusion | Gamma | Reactor | 2.26 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)
| Radiation | Radiation weighting factor |
|---|---|
| X-ray and gamma ray | 1 |
| Beta particles and positrons | 1 |
| Neutrons < 10 keV | 5 |
| Neutrons 100 keV – 2 MeV | 20 |
| Alpha particles | 20 |
External radiation: gamma and x-rays > beta > alpha
Internal radiation: alpha > beta > gamma and x-rays
For other dose effects see: Dose effects
| Organ | Tissue weighting factor |
|---|---|
| Skin, bone, brain, salivary glands | 0.01 |
| Bladder, oesophagus, liver, thyroid | 0.04 |
| Gonads | 0.08 |
| Red bone marrow, colon, lung, stomach, breast, remainder of tissues | 0.12 |
Protection
| Protection | Lead equivalence |
|---|---|
| Lead aprons | 0.25 mm for 100 kV 0.35 mm for 150 kV |
| Thyroid shields | 0.5 mm |
| Lead glasses | 0.25 x 1.0 mm |
| Lead gloves | 0.25 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 public | 1 mSv |
| Radiation workers < 18 yo | 6 mSv i.e. 3/10 of adult dose |
| Dose limit to abdomen of person of reproductive capacity | 13 mSv in any consecutive 3 months |
| Comforters and carers | 5 mSv |
| Any other person / member of public (fetus counts as members of the public) | 1 mSv |
| Pregnant employees dose to foetus | 1 mSv for remainder of pregnancy |
Equivalent dose limits per year:
| Area | Employees and trainees >18 yo | Trainees <18 yo | Any other person |
|---|---|---|---|
| Lens of the eye | 20 mSv | 15 mSv | 15 mSv |
| Extremities | 500 mSv | 150 mSv | 50 mSv |
| Skin | 500 mSv | 150 mSv | 50 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
| Radiograph | ESD per radiograph (mGy) | DAP per radiograph (Gy cm 2) |
|---|---|---|
| Abdomen AP | 4 | 2.5 |
| Chest AP | 0.2 | 0.15 |
| Chest PA | 0.15 | 0.1 |
| Cervical spine (AP and lat) | 0.3 | |
| Knee (AP and lat) | 0.6 | 0.6 |
| Lumbar spine AP | 5.7 | 1.5 |
| Lumbar spine lat | 10 | 2.5 |
| Pelvis AP | 4 | 2.2 |
| Shoulder AP | 0.5 | |
| Skull AP/PA | 1.8 | |
| Skull lat | 1.1 | |
| Thoracic spine AP | 3.5 | 1.0 |
| Thoracic spine lat | 7 | 1.5 |
| Adult CT | CTDI vol per sequence (mGy) | DLP per complete examination (mGy cm) |
|---|---|---|
| Head | 60 | 970 |
| Cervical spine | 21 | 440 |
| Chest | 12 | 610 |
| High-resolution CT chest | 4 | 140 |
| Chest, abdomen and pelvis | 1000 | |
| CT abdominal angiography | 15 | 1040 |
| CTPA | 13 | 440 |
| Abdomen | 14 | 910 |
| Abdomen and pelvis | 15 | 745 |
| Virtual colonoscopy | 11 | 950 |
| Kidneys, ureter and bladder | 10 | 460 |
| Urogram | 170 | |
| Coronary CT angiography | 170 – 380 |
| Paediatric CT | CTD vol per sequence (mGy) | DLP per complete examination (mGy cm) |
|---|---|---|
| Paeds head: 0-1 y | 25 | 350 |
| Paeds head: >1-5 y | 40 | 650 |
| Paeds head: <5 y | 60 | 860 |
| Adult CT-PET / CT-SPECT | CTDI vol per sequence (mGy) | DLP per complete examination (mGy cm) |
|---|---|---|
| PET half body | 4.3 | 400 |
| SPECT bone scan | 4.9 | 150 |
| SPECT parathryoid | 5.6 | 170 |
| SPECT mIBG / octreotide | 5.5 | 240 |
| SPECT cardiac | 21 | 36 |
Reporting overexposure:
| Accidental exposure | |
| Exposure category | Criteria for notification |
| All modalities including therapy | < 3 mSv effective dose (adult) < 1 mSv effective dose (child) |
| Unintended exposure | |
| Exposure category | Criteria 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 / cardiology | No procedural failure AND either: dose ≥ 10x local DRL OR observable deterministic effects excluding transient erythema |
| Radiotherapy pre-treatment planning scans | CT planning scan needs to be repeated twice to obtain appropriate data set (i.e. 3 scans in total including the intended scan) |
| Foetal – all modalities | Failure in the procedure for making pregnancy enquiries AND resultant foetal dose ≥ 1 mGy |
| Breast feeding infant – nuclear medicine only | Failure 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 mode | Rise of body core temperature (°c) | Head | Trunk | Extremities | SAR W/Kg |
| Normal | 0.5 | 38 | 39 | 40 | 2 |
| Controlled | 1 | 38 | 39 | 40 | 4 |
| Restricted | 2 | 39 | 40 | 41 | > 4 |
Hearing protection needed at 90 dB
Miscellaneous
Resolution
| Imaging modality | Resolution |
|---|---|
| Film screen radiograph | 6 lp/mm |
| Digital radiograph | 3 lp/mm |
| Film screen mammography | 15 lp/mm |
| Digital mammography | 5 to 10 lp/mm |
| Fluoroscopy | 1 lp/mm |
| Direct subtraction angiography | 2 lp/mm |
| Fluoroscopy – flat panel detector | 3 lp/mm |
| CT: transaxial | 2 lp/mm |
| CT: Z-sensitivity | 2 to 0.4 lp/mm |
Effective radiation dose
| Procedure | Dose | Procedure | Dose (mSv) |
|---|---|---|---|
| Abdominal | |||
| CT Abdo/pelvis | 10 | XR lower GIT | 3 |
| CT colonography | 6 | XR upper GIT | 6 |
| Barium enema | 7 | XR pelvis | 0.5 |
| CNS | |||
| CT head | 2 | XR cervical spine | 0.2 |
| CT spine | 6 | XR thoracic spine | 1.0 |
| CT neck | 3 | XR lumbar spine | 1.5 |
| XR skull | < 0.1 | ||
| Chest | |||
| CT chest | 7 | XR chest | 0.1 |
| Cardiac CT | 3 | Mammography | 0.4 |
| Cardiac CTA | 12 – 20 | ||
| Extremities | |||
| XR hand / foot | 0.005 | ||
| Nuclear imaging | |||
| Brain PET (18F FDG) | 14 | DEXA | 0.001 |
| Brain perfusion (99mTc HMPAO) | 9 to 10 | Renal MAG3 | 2 |
| Brain SPECT (99mTc sestamibi) | 10 | Renal DTPA | 2 |
| Bone scan | 6 | DaTscan brain | 6 to 10 |
| Heart stress (99mTc sestamibi) | 9.4 | V/Q | 2.5 |
| Thyroid scan | 5 | Gastric emptying | 1 |
| Whole PET/CT | 24 | ||
