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The Camera
NM DRUG MATH
BONUS
100

A wipe test swab produces a gross count of 1500cpm in a well counter with 56% efficiency. The background is 400cpm. Calculate the dpm produced by the swab.

1500cpm-400cpm/(0.56)= 1964dpm

100

Precision = _________________

Reproducibility
100
Calculate the sensitivity of a camera that produces 30,000 cpm with a 150uci source. Background is 300 cpm.

30,000-300 / 150= 198

Formula: Source cpm- background cpm / source activity

100
What is the decay constant of Tc-99m?

.693/6hr= .115

100
FORMULA FOR THYROID UPTAKE AND SCAN

(Thyroid counts- Thigh counts) / [ (Capsule -background)x decay factor] x 100%

200

What is the exposure rate at 1cm from an unshielded 30mCi dose of Tc99m. The exposure constant is 0.59Rcm2/mCi(h) at 1cm.

(30mCi)/(1cm)2 x 0.59Rcm2/mCi(h) = 17.7R/h

*** Note: Please watch your units!!! ***

200

Acccuracy=__________________

True Value

200

if a 128 x128 matrix is selected, how many pixels?

128 x128 = 16.384 pixels

200

A vial of DTPA is reconstituted with 100mci of Tc-99m. What will its activity be 4 hours later?

100mCi x e-.693x (4hr/6hr) = 63mci

200

Formula for LVEF

%EF = NET ED COUNTS - NET ES COUNTS/ NET ED COUNTS.x 100%

300

If you are exposed to a source for 4hours(why!?.. please don't ever be) what is the total radiation dose? The exposure rate of the source is 0.5mrem/hr?

(0.5mrem/hr) x 4hr = 2mrem


Formula: Total Dose = (dose rate)(time)

300

Calculate the 10% acceptable range for

195uci

195 *.10 = 19.5 

Range = 195-19.5 =175.5

             195 + 19.5 = 214.5

300
How many 128 x 128 frames can be simultaneously displayed on a 256 x 256 computer screen? 

(256pixels x 256 pixels) / (128pixels x 128 pixels) = 65,536/ 16,384 pixels = 4 frames

300
A 30lb child needs a bone scan. What dose should be given if you have an 20mci adult dose available?

Please use Clark's Formula

Clark's Formula: 30lb x 20mCi / 150lb = 4mci

400

If a source produces an exposure rate 350mrem/h at 3 inches from the surface, what is the exposure rate at 40inches.

350mrem x (3in)2 = I x (40in)2

=1.97 mrem

400
What is the percent error in constancy if the expected activity of a source is 1.5mCi and the actual activity reading is 1.1mCi? 

l 1.5mCi-1.1mCi l / (1.5mCi) x100% = 27%

400

How much memory is required for a 60-frame study using 64 x64 byte mode if the data are also stored in byte mode?

64 x 64x 60= 245,760

400
A 80lb child needs a gallium scan. The adult dose is 6 mCi. What dose should be administered?

(80 x 6 )/ 150= 3.2mCi

500

****** DAILY DOUBLE ******

What does ALARA stand for?

As Low As Reasonably Achievable

500

Calculate the correction factor for the 5uci dose level if the expected value is 10uci and the actual value is 12uci.

10/12= 0.83

Correction Factor = expected activity/ actual activity
500

**** DAILY DOUBLE ****

A 1,000,000 count SPECT study is to be performed on a phantom that produces a counting rate of 100,000cpm. If the acquisition is to have 62 stops over 360degree. What will be the total acquisition time, time per stop, and counts per stop?

Acquisition time: 1,000,000counts/100,000cpm = 10mins

Time per Stop: 10 min /62 stops = .16 min/stop 

Counts Per Projection: 1,000,000/ 62 stops = 16,129counts/stop

500

If a generator yields 500mCi when 600mci of Tc are actually present on the column, what is its percent efficiency?

500/600 x100= 83%