Introduction to Statistics :Introduction to Statistics By Jason Chok


Objectives :Objectives Define the meaning of statistics Identify areas where statistics be applied What importance is statistics in Nuclear Medicine Verify important calculations used in Nuclear Medicine Determine the statistics that can be applied in the camera uniformity flood


What is statistics? :What is statistics? Statistics is very important in every aspect of society examples of where it is used is in business, industry and government Inside these also falls nuclear medicine It is a way of summarizing data to aid understanding as creating graphical images of data Estimating the present and predicting the future Also drawing conclusions from data to make more accurate decisions


Areas where statistics is applied in Nuclear Medicine :Areas where statistics is applied in Nuclear Medicine Percentage errors or percentage differences in vials of expected value and actual Standard deviation of a series of values because of the randomness of radioactive decay It is also used to know when to calibrate instruments used depending on the precision of that particular equipment


Why is statistics important in nuclear medicine :Why is statistics important in nuclear medicine Because radioactivity is random it is hard to really tell when it is going to actually decay but, with a certain margin of correction it can be predicted Dose calibrators use statistics to estimate the percentage of correction to ensure precision is maintained Because we use machinery the chances of getting 100% all the time is impossible due to changes in the environment, and certain circumstances the measurement was taken


Important calculations in Nuclear Medicine :Important calculations in Nuclear Medicine Important calculations would include the daily constancy test used on dose calibrators Also the accuracy test on the dose calibrator; where the % of accuracy is tested and corrections is applied when needed When administering any radioactive material to patients the standard % that is allowed is determined using the decay factor These calculations can then be recorded and a Activity to time graph can be made to represent how much calibration is needed if any


Camera Uniformity Flood :Camera Uniformity Flood There are two methods one is Extrinsic and the other is Intrinsic Many things can affect the camera and the uniformity flood test is used to see by what degree has it fallen off the expected course Depending on the acquired image we can deduce what elements are off; resolution, collimator damage (if it is the extrinsic method), PMT offset, photo-peak settings, and sensitivity


Extrinsic Uniformity Flood :Extrinsic Uniformity Flood A collimator is used and a planar source With a count rate that does not exceed 30,000cps is centered over the detector A flood image is acquired that contains at least 3 million counts for a camera with a circular view and 5 million for one with a rectangular view If the camera has any uniformity correcting devices it can be turned off, images is taken with it on and off Then a comparison is made with previous uniformity images The data is then recorded, photopeak setting, CRT intensity setting, total counts, and elapsed imaging time Then the image is placed in the appropriate file


Intrinsic Uniformity Flood :Intrinsic Uniformity Flood The collimator is removed and extreme care is taken to avoid physical shock and radionuclide contamination of the crystal A lead mask ring of appropriate size is placed on the face of the detector A point source with a count rate of no more than 30,000 cps is placed at least 5 fields of view away from the crystals Then an image of at least 3 million for a circular and 5 million for a rectangular Field of view is taken Then if there is a correction system in place it will be taken with it on and off and the time for acquisition of the image is recorded and the images are evaluated for differences if any They are then compared to previous images for uniformity The date , photopeak setting, CRT intensity setting, total counts, and elapsed imaging time are recorded Then this data is placed in the appropriate file


Evaluation of the data for uniformity :Evaluation of the data for uniformity Window calculations = centerline energy +and- energy in keV x percent window/2 Camera sensitivity = source cpm – background cpm/source activity in uCi Acquisition time and counts per projection can be calculated Acquisition time = (# of prjections)(time per projection) Or = total counts/counting time Time per projection = total Acq. Time/ # of projections Counts per projection = total counts/# of projections Or = (time per projection)(counting rate)


Summary and Conclusion :Summary and Conclusion Statistics makes things with a large data set or a study over a period of time to be easily interpreted very important calculations in nuclear medicine because of the uses it has in prediction of the present and future; example pre-cal and decay factors We can now record data that can be evaluated and proper corrective measures taken Because of statistics a uniformity flood can be taken to ensure suitable working conditions for our cameras in the field


References :References The University Of Melbourne. The statistical consulting centre : what is statistics. Retrieved May 26, 2008, from http://www.scc.ms.unimelb.edu.au/whatisstatistics/ Edited by Paul E. Christian, Kristen M. Waterstram-Rich (2007). Nuclear Medicine and PET/CT Technology and Techniques (6th edition). Missouri : Mosby Elsevier Patricia Wells, Martha Pickett (1999). Practical Mathematics : in Nuclear Medicine Technology. Virginia : Society of Nuclear Medicine.


Question # 1 :Question # 1 A uniformity flood is taken with Tc99m what is the photopeak energy set at with a 20% window?


Answer for Q1 :Answer for Q1 The window must be set at 140keV +and- 10% Window setting = 140keV +and- 140keV x 10% = 140keV +and- 14keV =126keV – 154keV


Question #2 :Question #2 In a uniformity flood what is the maximum cps that can be used? a. 30kcps b. 30,000cps c. 300 cps d. Both a and b


Answer for Q2 :Answer for Q2 d. both a and b


Question #3 :Question #3 What are the two methods of testing uniformity in a routine camera QC procedure?


Answer for Q3 :Answer for Q3 Extrinsic and Intrinsic Methods


Question #4 :Question #4 What is a photopeak setting?


Answer for Q4 :Answer for Q4 It is the correct energy window for the radionuclide being used that must be selected, and the photopeak must be centered in that window


Question #5 :Question #5 In an intrinsic uniformity flood at what distance must we position the point source from the crystals useful field of view?


Answer for Q5 :Answer for Q5 It must be positioned at least 5 fields of view away