Nuclear Medicine Administered Activity Calculator

Administered activity scaled from a reference activity you supply, by eight methods side by side — because the published paediatric cards scale sublinearly in body weight, and a per-kilogram activity borrowed from an adult under-doses a 3 kg neonate by a factor approaching four.

Last updated 7 Oct 2026

A dose or dose rate calculated here is an estimate from a published model, not a measurement of anybody. Where a page prints a published limit beside its answer, that limit is there for comparison only — it is not permission and it is not a finding that an exposure is acceptable. Occupational and patient dose are governed by regulation and by local policy, and a dosimeter, a survey meter or a medical physicist's own calculation takes precedence over anything on this site.

Nuclear medicine administered activity

Reference activity and patient → scaled activity

Reference activity for a standard adultIn MBq, and it is YOUR number: this page does not carry one. The EANM Dosage Card and the North American consensus guidelines are the two standard sources and neither carries an open licence, so their tables are cited on this page rather than reproduced — and your own department’s protocol, or your national diagnostic reference level, is a better input than either. 400 MBq is a round placeholder and is not a recommendation for anything.

…for an adult of this weightIn kilograms. 70 kg is the conventional reference adult and is what most published reference activities are implicitly for. It matters because every weight-based method on this page is a RATIO to it: change it to 80 and every scaled activity falls by 12.5 per cent.

Patient weightIn kilograms, and it is the primary input for almost every method here. Note what weight does NOT do: it does not scale the activity linearly, except in the two rules that assume it does. Published paediatric dosage cards scale sublinearly for most agents, which means a small child needs MORE activity per kilogram than an adult, not less.

Patient heightIn centimetres. Used only by the three body surface area methods, which need both dimensions. If you do not have a height, use a weight-based method rather than guessing one: an error in height propagates to body surface area with an exponent between 0.40 and 0.73 depending on the formula, so a 10 per cent error in height is 4 to 7 per cent on the answer.

Patient ageIn years. Used only by Webster’s rule, which is the one method here that does not use weight at all — and that is both its convenience and its weakness, because two six-year-olds can differ by a factor of two in weight. It is included because it is still quoted, and because comparing it against the weight-based answers for the same patient is the quickest way to see how much it can be out by.

Scaling methodEight methods, and the headline follows whichever you pick — but every one of them is computed and printed below, which is the point of the page: at 20 kg they span a factor of 1.88, and the choice of method matters more than any input. The published dosage cards use neither linear weight scaling nor body surface area but a weight-dependent multiple that is, to within a few per cent, a POWER of body weight — and the exponent differs by radiopharmaceutical.

Power-law exponentOnly used by the power-law method. Fitted to the EANM card’s own published multiples, its three classes come out at 0.569, 0.863 and 1.126 — that is a fit done here, with an rms residual of 0.8 to 1.7 per cent, and not a figure the card prints. An exponent of 1 is linear weight scaling; about 0.70 is how body surface area grows with weight across the paediatric range; below that a small patient gets proportionally much more.

Activity per kilogramIn MBq/kg, and only used by the per-kilogram method. This is the form the North American consensus guidelines take — a per-kilogram activity with a minimum — and the figure has to come from them or from your own protocol, because this page does not reproduce their table. The value here is a neutral placeholder. For scale, published per-kilogram figures for common studies run from under 2 to around 10 MBq/kg.

Minimum recommended activityIn MBq. The floor: when the scaled activity falls below this, the minimum is administered instead, because below some activity the study simply does not produce a diagnostic image and the patient has been irradiated for nothing. Both standard sources carry a minimum for every agent, and the values differ by agent, which is why this is a field and not a constant. Set it to zero to see the unfloored scaling.

184.31MBqExample

A 20 kg, 115 cm, six-year-old, scaled from a 400 MBq adult reference by Haycock body surface area, with a 37 MBq floor

One reference activity, eight ways to scale it, and a floor

A = A_ref · f(patient) · A_given = max(A, A_min) · f = W/W_ref | BSA/1.73 | (W/W_ref)^p | (age+1)/(age+7)

A_ref: the reference activity for a standard adult, MBq, and the one number this page does not supply. The two standard sources — the EANM Dosage Card and the North American consensus guidelines — carry no open licence, so their tables are cited here and not reproduced; a departmental protocol or a national diagnostic reference level is a better input than either, because it already accounts for the cameras and acquisition times you have
W/W_ref: linear scaling in body weight, the intuitive choice and the one that under-doses small children. It is what a per-kilogram activity amounts to, and it is what Clark’s rule is in disguise: 150 pounds is 68.04 kg, so Clark’s rule is weight scaling with a 68 kg reference adult
BSA/1.73: body surface area scaling, against the conventional reference adult of 1.73 m². Three published formulas — Du Bois and Du Bois (1916), Haycock (1978) and Mosteller (1987) — agree with each other to within 1.4 per cent between 20 and 70 kg and to within 5.7 per cent anywhere from a 3 kg neonate to a 100 kg adult, and all three put an exponent well below 1 on weight, which is why surface-area scaling gives a small patient substantially more than weight scaling does
(W/W_ref)^p: a power law in weight, which is what a published dosage card’s multiples actually are. Fitted here to the EANM card’s thirty published weight rows, its three classes come out at p = 0.569, 0.863 and 1.126, with rms residuals of 0.8, 1.7 and 1.6 per cent. Those three exponents are a fit done here and not figures the card prints. p = 1 is linear; p of about 0.70 is how surface area grows with weight across the paediatric range, fitted here over eight representative weight-and-height pairings; the lowest class is below even that
(age+1)/(age+7): Webster’s rule, the one method here that uses no weight at all. Its convenience is also its defect: it gives one answer for every child of a given age, and two six-year-olds can differ by a factor of two in weight. It is on the page because it is still quoted, and because comparing it with the weight-based answers for the same patient shows how far out it can be
A_min: the minimum recommended activity, MBq, and the part of the method that is not a curve. Below some activity a study simply does not collect enough counts to be reportable, and a patient irradiated for an unreportable image has received dose for nothing — so both standard sources carry a floor for every agent and the floor overrides the scaling. It is agent-specific, which is why it is a field here and not a constant
counts, not dose per kilogram: the reason every published card scales sublinearly, and the thing to understand rather than memorise. Image noise falls as the square root of the number of counts collected, and the counts depend on the activity in the organ of interest, the organ’s size, the attenuation between it and the camera and the acquisition time — none of which scales with body mass. A smaller patient attenuates less but presents a smaller target, and the net effect is that holding image quality constant needs more activity per kilogram, not the same

Worked example

A 20 kg, 115 cm, six-year-old, scaled from a 400 MBq adult reference by Haycock body surface area, with a 37 MBq floor
THE REFERENCE ACTIVITY IS YOURS, AND 400 MBq IS A PLACEHOLDER. This page carries no reference activities, because the two standard sources — the EANM Dosage Card version 5.7.2016 and the 2024 North American consensus guidelines — were both read for this batch and neither carries a licence permitting reproduction. So the number to put in is your department's own protocol figure, or your national diagnostic reference level, which is a better input in any case
THE BODY SURFACE AREA. Haycock's formula is 0.024265 × W^0.5378 × H^0.3964, which at 20 kg and 115 cm gives 0.7971 m². Mosteller's gives 0.7993 and Du Bois's 0.8004 — the three disagree by 0.41 per cent, which is nothing, so the choice between them does not matter and the choice of METHOD does
THE SCALING. 0.7971 ÷ 1.73 = 0.4608 of the reference adult's surface area, so the activity is 400 × 0.4608 = 184.3 MBq. The 1.73 m² is a convention from the 1920s that nothing measures and that the whole literature is written in
AND NOW COMPARE IT WITH LINEAR WEIGHT SCALING, WHICH IS THE WHOLE POINT. 20 kg is 20/70 = 0.2857 of the reference adult's weight, which would give 114.3 MBq. Surface-area scaling gives 1.61 TIMES that. Webster's age rule at six years gives 215.4, which is 1.88 times the linear answer. Clark's rule gives 117.6 — almost exactly the linear answer, because 150 pounds is 68.04 kg and Clark's rule is linear weight scaling in disguise. Eight methods, one patient, a spread of 1.88 times
WHAT THE PUBLISHED CARDS ACTUALLY DO, AND IT IS NEITHER OF THOSE. The EANM card multiplies a baseline activity by a weight-dependent MULTIPLE, with three classes for different radiopharmaceuticals. Fitted to its own thirty published weight rows, those multiples are power laws in weight at exponents of 0.569, 0.863 and 1.126, with rms residuals of 0.8, 1.7 and 1.6 per cent. Those exponents are a fit done here, not figures the card prints, and the card's table is not reproduced on this site. At 20 kg the lowest class gives 400 × 0.4900 = 196.0 MBq
WHY TWO OF THE THREE EXPONENTS ARE BELOW 1, which is the thing to take away. Image noise depends on the number of COUNTS collected, not on the dose per kilogram. A smaller patient attenuates less, which helps, but presents a smaller organ to the camera, which does not — and neither effect scales with body mass. Holding image quality constant therefore needs MORE activity per kilogram in a small child, not the same. On the lowest class a 3 kg neonate receives 3.88 times the adult's activity per kilogram and a 10 kg infant 2.31 times. Scale an adult activity linearly by weight and the neonate gets an image too noisy to report, having been irradiated for it anyway
THE FLOOR, WHICH IS WHERE THE CURVE STOPS. Below some activity no acquisition is diagnostic, so both standard sources carry a minimum recommended activity per agent that overrides the scaling. At 37 MBq and a 400 MBq reference, linear scaling hits the floor below 6.47 kg; on the 0.569 power law it does not bind until 1.07 kg, because the curve is already far above linear down there. At 20 kg the floor is not binding and the answer is 184.3 MBq
WHAT TO DO WITH THE NUMBER. Draw it on the decay-correction page on this site, which answers the question this page does not: what volume to withdraw from a vial calibrated at a different time. The activity here is a SCALING of a reference figure you supplied; it is not a prescription, it carries no organ dose, and the EANM card's own framing applies to it — these are recommendations in the context of good practice, they do not substitute for national or international legal or regulatory provisions, and diagnostic reference levels must not be exceeded

Why linear per-kilogram scaling under-doses a small child

Every column is a FRACTION of the reference adult’s, so the table is independent of whatever reference activity you use. The second column is linear scaling and the next three are power laws at the exponents the EANM Dosage Card’s three classes follow — a least-squares fit done here across the card’s thirty published weight rows, with an rms residual of 0.8 per cent for the lowest class, 1.7 for the middle one and 1.6 for the highest, and a worst single residual of 6.1 per cent. THE CARD’S OWN TABLE IS NOT REPRODUCED ANYWHERE ON THIS SITE: it carries no open licence, so what is printed here is an analysis of it rather than a copy, and the card itself has to be consulted for the multiples and the baseline activities. The last two columns are the point. A 3 kg neonate on the lowest class receives 3.88 times the adult’s activity PER KILOGRAM, and a 10 kg infant 2.31 times. The reason is not generosity: image noise depends on the number of counts collected, and a smaller patient attenuates less and presents a smaller organ to the camera, neither of which scales with body mass. Scale an adult activity by weight alone and the small child gets an image too noisy to report, having been irradiated anyway. This estimates a dose from a published model and a set of typical factors. It is not a measurement of any patient and it is not a dosimetry report. Patient dose is the responsibility of the medical physicist and the practitioner, and a patient-specific figure needs the actual exposure parameters, not a typical one.
Weight (kg)	Fraction of adult WEIGHT	Fraction of adult activity at exponent 0.569	…at 0.863	…at 1.126	Activity per kg against an adult’s, at 0.569	…at 0.863
3	0.0429	0.1664	0.0659	0.0288	3.882×	1.538×
5	0.0714	0.2225	0.1024	0.0512	3.115×	1.434×
10	0.1429	0.3302	0.1864	0.1118	2.312×	1.304×
15	0.2143	0.4160	0.2645	0.1765	1.941×	1.234×
20	0.2857	0.4900	0.3390	0.2440	1.715×	1.187×
30	0.4286	0.6173	0.4812	0.3852	1.440×	1.123×
40	0.5714	0.7271	0.6168	0.5326	1.272×	1.079×
50	0.7143	0.8256	0.7479	0.6847	1.156×	1.047×
70	1.0000	1.0000	1.0000	1.0000	1.000×	1.000×

Every scaling method, on one 400 MBq reference, across the paediatric range

All activities in MBq, from a 400 MBq adult reference at 70 kg — a round placeholder, not a recommendation. The heights and ages are representative pairings for the weights so that the methods can be compared at all; they are not growth-chart values and no minimum activity has been applied. Read the last column first: body surface area scaling gives 2.79 times the linear answer for a 3 kg neonate, 1.61 times at 20 kg, and 1.06 at adult size — so the methods agree where it does not matter and disagree where it does. Webster’s age rule is the outlier and the warning: it uses no weight at all, so it gives one answer for every child of a given age, and at six years that is 215 MBq whether the child is 15 kg or 30. Clark’s rule looks like a separate method and is not — 150 pounds is 68.04 kg, so Clark’s rule IS linear weight scaling with a 68 kg reference adult, which is why its column tracks the linear one to within three per cent all the way down. The power-law column is what a published dosage card’s lowest class actually does, and it sits between the linear and the surface-area answers at every weight. This is a first-pass calculation on an idealised geometry — a point source, a uniform slab, no self-absorption in the source, no container, no floor and no walls. Real sources have extent and encapsulation, and real rooms scatter. A closed-form answer cannot see any of that.
Weight (kg)	Height (cm)	Age (y)	Linear in weight	BSA, Mosteller	BSA, Haycock	Webster’s age rule	Clark’s rule	Power law at 0.569	Haycock ÷ linear
3	50	0.0	17.1	47.2	47.8	57.1	17.6	66.5	2.79×
6	65	0.5	34.3	76.1	76.9	80.0	35.3	98.8	2.24×
10	76	1.0	57.1	106.2	107.7	100.0	58.8	132.1	1.89×
20	115	6.0	114.3	184.8	184.3	215.4	117.6	196.0	1.61×
30	138	10.0	171.4	247.9	246.4	258.8	176.4	246.9	1.44×
50	160	14.0	285.7	344.7	343.9	285.7	293.9	330.3	1.20×
70	170	30.0	400.0	420.4	422.1	335.1	411.5	400.0	1.06×

Three published body surface area formulas, and where they disagree

Body surface area in square metres. All three are equations rather than tables and all three are universally reproduced, so the useful question is not which is right but how much it matters — and the answer is mostly reassuring, with one exception worth knowing. Between 20 and 70 kg the three agree to within 1.4 per cent, against a 61 per cent difference between surface-area scaling and weight scaling at 20 kg — so the choice between the formulas is immaterial there. At the ends it is larger: 5.7 per cent for a 3 kg neonate, 5.5 for a 10 kg infant and 3.1 for a 100 kg adult, which is still small against the choice of method and is large enough to be worth picking one formula and staying with it. Pick whichever your department uses. Mosteller’s is the one worth remembering because you can do it in your head: the square root of weight times height over 3600. The exponents are where the physiology is. Du Bois puts 0.425 on weight and 0.725 on height; Haycock 0.538 and 0.396; Mosteller exactly 0.5 on each. All three say the same thing in different proportions — surface area grows far more slowly than weight — and Haycock’s weight exponent of 0.538 is within six per cent of the exponent the EANM card’s lowest class turns out to follow, which is probably not a coincidence. The last column is the convention nothing measures: the reference adult 1.73 m², a 1920s normalisation retained because the whole literature is written in it.
Weight (kg)	Height (cm)	Du Bois 1916	Mosteller 1987	Haycock 1978	Spread (%)	Haycock ÷ 1.73 m²
3	50	0.1954	0.2041	0.2066	5.72	0.1194
10	76	0.4415	0.4595	0.4659	5.53	0.2693
20	115	0.8004	0.7993	0.7971	0.41	0.4608
40	150	1.3029	1.2910	1.2858	1.33	0.7432
70	170	1.8097	1.8181	1.8257	0.88	1.0553
100	180	2.1950	2.2361	2.2624	3.07	1.3077

What the two standard sources actually contain, and why neither is tabulated here

This table exists because the licensing position changes what the page can show you, and hiding that would be worse than stating it. The two standard sources are both freely downloadable and neither carries a licence permitting reproduction, so this page reproduces neither — which turns out to make it a more useful tool rather than a less useful one, because the reference activity is the part a department already has and the scaling is the part that is easy to get wrong. The one derived figure that IS printed, the fitted power-law exponent of each EANM class, is an analysis of the card and is labelled as such everywhere it appears. Note the difference in FORM between the two sources, which is a real and under-discussed disagreement: a per-kilogram activity with a floor is linear scaling plus a minimum, and a weight-dependent multiple is a smooth sublinear curve. The two therefore diverge most for the smallest patients, which is precisely who they were written for. This estimates a dose from a published model and a set of typical factors. It is not a measurement of any patient and it is not a dosimetry report. Patient dose is the responsibility of the medical physicist and the practitioner, and a patient-specific figure needs the actual exposure parameters, not a typical one.
Source	Form of the recommendation	Licence found	What this page does with it
EANM Dosage Card, version 5.7.2016	Administered activity = a baseline activity for the radiopharmaceutical, times a weight-dependent MULTIPLE; three classes with different multiples for the same weight; a minimum recommended activity per agent that overrides the calculation. Multiples tabulated for weights from 3 to 68 kg	None found. No open licence or reuse statement on the card	Cited and not reproduced. The method is stated on this page; the multiples and baseline activities are not. One derived statistic is printed — the power of body weight each class follows, fitted here by least squares with the residual stated
North American consensus guidelines, 2024 update	A per-kilogram activity per study, with a minimum activity; some studies given as a RANGE of MBq/kg and some as a single value	None found. No copyright or licence statement on the document	Cited and not tabulated. The per-kilogram field on this page takes the figure from the reader. Two values are quoted in this page’s reference list to show the shape of what the document contains
AAPM Report No. 96 (for the CT comparison on the sibling page)	Not an activity source; cited here only because the same licensing question arose on the CT page in this batch	“All rights reserved”, 2008	Cited by number only; its table of coefficients is not reproduced anywhere in this plugin
Your own department’s protocol or national reference level	Whatever it says	Yours	This is the input this page is designed around, and it is the better one: a local protocol already accounts for the cameras, the acquisition times and the reporting standards you actually have

Eight ways to scale one reference activity, and why the obvious one is the wrong one

The reference activity is yours, and that is a licensing decision rather than an omission. Two sources set paediatric administered activities in practice: the EANM Dosage Card, version 5.7.2016, and the North American consensus guidelines, updated in 2024. Both were read for this batch. Neither carries a licence permitting reproduction — the card has no reuse statement and the guidelines document has no copyright statement at all — so neither table is on this page. What is on this page is the METHOD, which is the part that is easy to get wrong, with the reference activity taken from you. That turns out to be the better tool anyway: a department’s own protocol figure already accounts for the cameras, the acquisition times and the reporting standards it actually has, and a national diagnostic reference level is the number that has to be respected in any case.

Linear per-kilogram scaling under-doses a small child, and the reason is counts rather than dose. This is the one thing to take from the page. Image noise falls as the square root of the number of counts collected, and the counts depend on the activity in the organ being imaged, the size of that organ, the attenuation between it and the camera, and the acquisition time. None of those scales with body mass. A smaller patient attenuates less, which helps, but presents a smaller target, which does not — and the net is that holding image quality constant takes MORE activity per kilogram in a small child, not the same. That is why every published dosage card scales sublinearly for most agents, and why a per-kilogram figure borrowed from an adult protocol produces an image too noisy to report in a neonate who has been irradiated for it regardless.

How far sublinear, measured. The EANM card’s multiples are, to within a few per cent, power laws in body weight. Fitted here by least squares across the card’s thirty published weight rows, its three classes come out at exponents of 0.569, 0.863 and 1.126, with rms relative residuals of 0.8, 1.7 and 1.6 per cent and a worst single residual of 6.1 per cent. Those three numbers are an analysis of the card and not a copy of it, and they are labelled as a fit wherever they appear on this site; the card itself has to be consulted for the multiples and for which class an agent belongs to. What they buy is an intuition no rule of thumb offers. On the lowest exponent a 3 kg neonate receives 3.88 times the adult activity per kilogram and a 10 kg infant 2.31 times; the middle class is 1.54 and 1.30 times; and the highest class is slightly SUPERlinear, which is not what most people expect and is why the card has three classes rather than one curve.

The two standard sources disagree in FORM, not just in numbers. The North American guidelines give a per-kilogram activity with a minimum, which is linear scaling plus a floor. The EANM card gives a weight-dependent multiple, which is a smooth sublinear curve. Those two shapes diverge most for exactly the patients both documents were written for: in the smallest children a flat MBq/kg gives a fraction of what a sublinear multiple gives, until the floor takes over and the two meet again from a different direction. Both approaches are current, both are in daily use on different continents, and neither is an error. The page computes both forms side by side so the difference is a number rather than an argument.

Body surface area is a good approximation to the right answer, and the three formulas for it hardly matter. Du Bois and Du Bois (1916), Haycock (1978) and Mosteller (1987) agree with each other to within 1.4 per cent between 20 and 70 kg, and to within 5.7 per cent anywhere from a 3 kg neonate to a 100 kg adult — against a 61 per cent difference between surface-area scaling and weight scaling at 20 kg. So pick whichever your department uses and do not worry about it; Mosteller’s is the square root of weight times height over 3600 and can be done in your head. All three put an exponent well below 1 on weight — 0.425, 0.538 and 0.5 respectively — which is the physiological content: surface area grows far more slowly than mass. Haycock’s 0.538 is within six per cent of the exponent the EANM card’s lowest class turns out to follow, which is unlikely to be an accident.

What this page is not, and what to do next. It is not a prescription. It computes no absorbed dose to any organ and makes no statement about any patient’s risk; it scales a number you supplied. The EANM card’s own framing applies and is worth repeating: its recommendations should be taken in the context of good practice, they do not substitute for national or international legal or regulatory provisions, and diagnostic reference levels must not be exceeded. What this page pairs with is the decay arithmetic: an activity you have decided on is not a volume you can draw, because the vial was calibrated at a different time and the concentration has been falling ever since. The decay-correction page on this site does that half, and for a six-hour nuclide the difference between the calibration time and the injection time is routinely a factor of two.

Frequently asked questions

How do I work out a child’s administered activity?

Take the adult reference activity for the study from your own protocol or from a published dosage card, and scale it — but not linearly by weight, which is the intuitive thing to do and under-doses small children badly. The published cards scale by a weight-dependent multiple that is, to within a few per cent, a power of body weight below 1 for most agents, so a small child needs MORE activity per kilogram than an adult. Then apply the minimum recommended activity for the agent as a floor, because below some activity the study is not reportable and the patient has been irradiated for nothing. This page does all of that from a reference activity you supply; it does not carry reference activities, because the two standard sources carry no licence permitting their tables to be reproduced.

Why not just scale the adult activity by weight?

Because image quality depends on COUNTS, and counts do not scale with body mass. Noise in a nuclear medicine image falls as the square root of the number of counts collected, and the counts depend on the activity in the organ being imaged, that organ’s size, the attenuation between it and the camera, and the acquisition time. A smaller patient attenuates less, which helps; but the organ is smaller, so it holds less activity and subtends a smaller solid angle, which does not. The net effect is that holding image quality constant needs more activity per kilogram in a small child. On the exponent the EANM card’s lowest class follows, a 3 kg neonate gets 3.88 times the adult per-kilogram activity and a 10 kg infant 2.31 times. Weight scaling gives a neonate about a quarter of that, and the result is an unreportable image from a real dose.

Should I use body surface area or body weight?

Body surface area is much closer to what the published cards do and is the better of the two if those are your only options: at 20 kg it gives 1.61 times the linear answer, and the cards’ own lowest class sits between the two. But neither is what the cards actually use, and if you have the card you should use the card. A useful way to see why surface area works at all: all three published surface-area formulas put an exponent well below 1 on weight — 0.425 for Du Bois, 0.5 for Mosteller, 0.538 for Haycock — and Haycock’s is within six per cent of the exponent the EANM card’s lowest class turns out to follow. Surface-area scaling is a sublinear weight scaling with a height correction attached, and the sublinearity is the part that matters.

Which body surface area formula should I use?

It genuinely does not matter. Du Bois and Du Bois (1916), Haycock (1978) and Mosteller (1987) agree with each other to within 1.4 per cent between 20 and 70 kg and to within 5.7 per cent anywhere from a 3 kg neonate to a 100 kg adult, which is far smaller than any other choice on this page. Use whichever your department uses. Mosteller’s is worth remembering because it is the square root of weight in kilograms times height in centimetres over 3600, which can be done mentally. The one number in all three that is worth knowing is NOT measured: the reference adult body surface area of 1.73 m² is a 1920s normalisation retained because the literature is written in it, and every surface-area scaling in medicine is a ratio to it.

What is the minimum administered activity for, and can I ignore it?

It is there to prevent a useless exposure, so no. Below some activity an acquisition does not collect enough counts to produce a reportable image in the available time, and a patient who has been irradiated for an unreportable study has taken the dose and received none of the benefit. So the floor is a dose-reduction measure rather than a permission: it stops you scaling an activity down into uselessness. Both standard sources carry a minimum for every agent and the values differ by agent. Where you have latitude, the alternative to more activity is more TIME — a longer acquisition collects the same counts from less activity, and in a sedated or swaddled infant that is often available in a way it is not in an adult who has to lie still voluntarily.

Is Webster’s rule still usable?

It is still quoted and it is the weakest method on this page, for one reason: (age+1)/(age+7) uses no weight at all, so it gives the same answer for every child of a given age. At six years it returns 0.538 of the adult activity whether the child weighs 15 kg or 30 kg, and a factor of two in weight at the same age is entirely ordinary. Comparing it with the weight-based rows for the same patient is the quickest demonstration of what it costs. It is also oddly shaped at the top end: it approaches 1 only asymptotically, so at eighteen it gives 0.76 of an adult activity for somebody who may weigh more than the reference adult. If you have a weight, use a method that uses it.

Is Clark’s rule different from weight scaling?

No, and this is worth knowing because it looks like a separate method and is quoted as one. Clark’s rule is the patient’s weight in pounds divided by 150, times the adult dose. One hundred and fifty pounds is 68.04 kilograms, so Clark’s rule is exactly linear weight scaling with a 68 kg reference adult rather than a 70 kg one — a three per cent difference and nothing else. Everything that is wrong with linear weight scaling in a small patient is therefore wrong with Clark’s rule, and the page prints both columns so they can be seen tracking each other all the way down. It is on the page for the same reason Webster’s rule is: somebody arriving with it deserves to see what it does rather than be told not to use it.

Why does this page not list the activities for each study?

Because the two sources that carry them do not licence their reproduction. The EANM Dosage Card, version 5.7.2016, was read in full for this batch: it gives a baseline activity and a minimum recommended activity for each radiopharmaceutical, a class assignment, and a table of weight-dependent multiples from 3 to 68 kg. No reuse statement was found on it. The 2024 update of the North American consensus guidelines gives per-kilogram activities with minima, and carries no copyright statement at all. Rather than reproduce either table, this page takes the reference activity from you and does the scaling, which is the part that is easy to get wrong. One derived statistic about the EANM card IS printed — the power of body weight each of its three classes follows, fitted here with the residual stated — because that is an analysis of the card rather than a copy of it, and because it is the single most useful thing to know about paediatric activity scaling.

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References

EANM Dosage Card (version 5.7.2016), Paediatric and Dosimetry Committees of the European Association of Nuclear Medicine (read in full, 7 October 2026). CITED AND NOT REPRODUCED: no open licence was found on it, so neither its table of weight-dependent multiples nor its baseline activities are printed here. What is taken is the method, which is stated on the page: administered activity is a BASELINE ACTIVITY multiplied by a weight-dependent MULTIPLE, “A[MBq]_Administered = Baseline Activity × Multiple”, with each radiopharmaceutical assigned to one of three classes that have different multiples for the same weight, and with a MINIMUM RECOMMENDED ACTIVITY that overrides the calculation when the weight-scaled figure falls below it. The multiples run over weights from 3 to 68 kg. One derived statistic about the card is printed: the power of body weight each class follows, fitted here by least squares in log space, with the residual measured and stated beside it. The card is also quoted for its own framing, which the page repeats: the recommendations “do not substitute for national and international legal or regulatory provisions” and should be taken in the context of good practice, and diagnostic reference levels must not be exceeded.
2024 Update of the North American Consensus Guidelines for Pediatric Administered Radiopharmaceutical Activities, Society of Nuclear Medicine and Molecular Imaging (read 7 October 2026). CITED AND NOT TABULATED: no copyright or licence statement was found on the document, so the page does not reproduce its table and takes the reference activity from the reader instead. Two figures are quoted here to show the shape of what it contains, because a reader needs to know what they are looking for: fluorine-18 FDG for a body study at “2.96-5.2 MBq/kg (0.08-0.14 mCi/kg)” with a minimum of “26 MBq (0.7 mCi)”, and technetium-99m MDP for a bone scan at “9.3 MBq/kg (0.25 mCi/kg)” with a minimum of “37 MBq (1.0 mCi)”. Note the FORM of both: a per-kilogram activity WITH A FLOOR, which is linear-in-weight scaling plus a minimum rather than the smooth sublinear curve the EANM card uses, and the two therefore diverge most for the smallest patients. Note also that the FDG entry is a RANGE and the MDP entry is not, which is a statement about how settled each protocol is.
G. B. Haycock, G. J. Schwartz and D. H. Wisotsky, Geometric method for measuring body surface area: a height-weight formula validated in infants, children and adults, Journal of Pediatrics 1978;93(1):62–66, cited for its formula BSA = 0.024265 · W^0.5378 · H^0.3964, alongside Du Bois and Du Bois (1916), BSA = 0.007184 · W^0.425 · H^0.725, and Mosteller (1987), BSA = √(W·H/3600). The three are equations rather than tables and all three are universally reproduced; what matters on the page is where they DISAGREE. At 20 kg and 115 cm they give 0.7971, 0.8004 and 0.7993 m² — 0.4 per cent apart, which is nothing. The weight exponents are the interesting part: Haycock’s 0.538 is a statement that surface area grows far more slowly than weight, and it is within a few per cent of the exponent the EANM card’s lowest class turns out to follow. Note also the convention the page uses and that nothing measures: the reference adult body surface area of 1.73 m², which is a 1920s normalisation retained because the literature is written in it.
A. Pearce, NPL Report IR 6: Recommended Nuclear Decay Data, National Physical Laboratory. Crown copyright — cited, not reproduced, and used here through this plugin’s `_nuclide_data.py` for the gamma line energies and emission probabilities that the air kerma rate constant is derived from. VIA THE DATA MODULE. The lines matter more here than on the decay pages, because the derivation is a sum over them: caesium-137 contributes one line at 661.657 keV with a yield of 0.851, cobalt-60 two at 1173.228 and 1332.492 keV at essentially one each, and iridium-192 nine between 205.794 and 612.462 keV summing to 2.135 photons per decay. The list is of PRINCIPAL GAMMA lines only, which is the whole reason the derived constant is a few per cent below the published one for a clean gamma emitter and a factor of several below it for an electron-capture nuclide.
Backgrounder on Biological Effects of Radiation, United States Nuclear Regulatory Commission, nrc.gov (read 7 October 2026). A US Government work and reproduced. The source for the background comparison figure: “On average, a U.S. resident receives an annual radiation exposure from natural sources of about 310 millirem (3.1 millisieverts)”, with man-made sources adding roughly another 310 for a total of about 620 mrem a year, of which computed tomography alone is about 150. It also notes that radon and thoron account for two thirds of the natural component, which is the reason the figure varies so much between places and the reason the field is editable on this page: the average is a national average over a quantity dominated by local geology.
ICRP Publication 60 (1990) and ICRP Publication 103 (2007), the two generations of the Commission’s recommendations whose tissue weighting factors the CT coefficients on this page are computed with. CITED BY NUMBER ONLY. Nothing from either is reproduced and in particular the tissue weighting factors w_T are not reproduced in any vintage, here or anywhere else in this plugin — both publications are copyrighted and neither was read for this batch. They are referenced for the one structural fact the page depends on: effective dose is a weighted sum of organ doses, the weights were revised between the two publications, and a coefficient computed under one definition is not comparable with a coefficient computed under the other. Where a reader needs the weights themselves, 10 CFR 20 carries an older public-domain set whose vintage would have to be stated; this batch did not need them and does not print them.