Physics and Radiobiology of Nuclear Medicine

Answer
True positive = 780
True negative = 160 − 15 = 145
False negative = 840 − 780 = 60
False positive = 15

Questions

1. Define accuracy and precision.


2. Do systematic errors give an accurate measurement? Can systematic
   errors give a precise measurement?


3. A radioactive sample gives 15,360 counts in 9 min:
   (a) What are the count rate of the sample and its standard deviation?
   (b) If the sample contained a background count rate of 60 cpm obtained
   from a 2-min count, what would be the net count rate of the sample
   and its standard deviation?


4. How many counts of a sample are to be collected to have a 1% error at
   the 95% comfidence level?


5. Within how many standard deviations of a mean count of 62,001 is 730?


6. To achieve an estimated percent standard error of 3%, how many counts
   must be collected?


7. The c^2 value of 11 measurements of a quantity is 4.2. What is the prob-
   ability that the variations of measurements are due to statistical varia-
   tions of the quantity?

Suggested Readings

Bahn AK.Basic Medical Statistics.New York: Grune & Stratton; 1972.
Martin PM. Nuclear medicine statistics. In: Rollo FD, ed.Nuclear Medicine Physics,
Instrumentation and Agents.St. Louis: Mosby; 1977:479–512.

Negative predictive value =

+

=×=

145

145 60

145

205

100 70 7.%

Positive predictive value =

+

=×=

780

780 15

780

795

100 98 1.%

Accuracy=

+

+++

=×=

780 145

780 145 60 15

925

1000

100 92 5.%

Specificity=

+

=×=

145

145 15

145

160

100 90 6.%

Sensitivity=

+

=×=

780

780 60

780

840

100 92 6.%

Suggested Readings 43