Uniformity Flood (Quality Control of gamma camera )

Uniformity Flood

1.   الاختبار اللى بيوضح مدى التجانس فى الصوره بين الPixels  حيث انه بيختبر مدى الvariation بين الPixels  فى الintensity values

2.        ممكن يتم الاختبار فى وجود الCollimator ويطلق عليه extrinsic او فى عدم وجوده ويطلق عليه intrinsicntrinsic

3.             

Intrinsic flood

-يتم ازاله الcollimator  من الhead of camera

2-يتم استخدام مصدر من ال 99mTC له نشاط اشعاعى اقل من 1mci

    3- يتم وضع الِSyringe Activity of 99mTC على مسافه اكبر من 5 FOV  للجاما كاميرا     

      4-لابد ان يكون الcount rate  اقل من 20KCPs وده لاجل تلافى تاثير ال Dead time للجاما كاميرا

.  5-لاحظ انك لو شغال على جاما كاميرا dual head  هاتستخدم مصدر قوته 100-250 uci ويوضع فى المنتصف بين الBoth Head

6-بعض الsystems تتطلب انك تضع Lead Mask 

Lead Mask يوضع حول اEdge  لل crystal   حتى يمنع

the interaction between crystal edge and gamma rays

Extrinsic Flood

a.            يتم استخدام ال sheet of Co57 او 

refillable flood with 5 - 15 mCi of ^99mTc

b.            يتم وضع الflood او ال sheet على ال  collimator surface

c.            ولو انا عندى     dual head gamma camera

d.            هايتم وضع الflood  كما هو موضح بالشكل عن طريق استخدام 4 styrofoam cups  من اسفل وواحد من اعلى للحفاظ على تساوى المسافه بين الcollimators of both head  وال flood

Flood

Intrinsic/extrinsic uniformity

1-    اولا لازم تتاكد من الPeak  عن طريق الPhotopeak test

2-    ظبط الacquisition على انه يعمل Collection ل 2-6 Million Counts

3-    الFlood لابد ان يكون خالى من اى air bubblesر

Extrinsic Flood

                                        a.            يتم استخدام ال⁵⁷Co sheet or a refillable flood with 5 - 15 mCi of ^99mTc

                                        b.            يتم وضع الflood او ال sheet على ال  collimator surface

                                        c.            ولو انا عندى     dual head gamma camera

                                        d.            هايتم وضع الflood  كما هو موضح بالشكل عن طريق استخدام 4 styrofoam cups  من اسفل وواحد من اعلى للحفاظ على تساوى المسافه بين الcollimators of both head  وال flood

Flood

Intrinsic/extrinsic uniformity

1-    اولا لازم تتاكد من الPeak  عن طريق الPhotopeak test

2-    ظبط الacquisition على انه يعمل Collection ل 2-6 Million Counts

3-    الFlood لابد ان يكون خالى من اى air bubbles

                           e.        Two quantification formulas (you must know)

                                                                     i.        Integral uniformity evaluates the entire flood at the pixel level and finds the pixel with the least counts and the one with the most counts. Apply those numbers to the above formula. This gives you an overall picture on how uniform the flood is. Over time, if the % slowly increases then service dude needs to called in for a PM

                                                                    ii.        Differential uniformity looks a 5 pixel segment, either vertically or horizontally and determines what the counts are in each pixel. The one with the most and less counts are placed into the formula. This value shows non uniformity over a small segment of the camera

                                                                   iii.        Integral uniformity will always be greater or equal, but never less than differential uniformity (why?)

                            f.        Example I

                                                                     i.        Both integral and differential calculations are displayed with FFOV (Full Field of View) and CFOV (Center Field of View)

                                                                    ii.        To the left is a Levy-Jenning plot where the solid line is the FFOV and the dotted is CFOV for intergral and differential uniformity over time

                                                                   iii.        Evaluation of these calculations and graphs, over time, will determine when the system needs to be re-tuned

                           g.        Example II - Goal of this system is to find the area of the greatest non-uniformity

                                                                     i.        Boxes indicate the area of greatest non uniformity in the UFOV (Useful Field of View) and CFOV. This generates intergral uniformity for both views. Is there advantage to not FFOV?

                                                                    ii.        Boxes can be moved around at the discretion of the user

                                                                   iii.        The greatest non-uniformity within each box displays a differential uniformity via the veritical and horizontal line in the UFOV and CFOV

                           h.        Additional comments

                                                                     i.        What are the differences between FFOV, UFOV, and CFOV?

                                                                    ii.        FFOV cover the entire detector's surface, however, counts tend to fluxuate at the extreme edges of the FOV which is caused by edge packing. This may falsely elevate the integral value

                                                                   iii.        UFOV is 95% of the FOV's area. Notice the outline drawn slightly inside the edge of the crystal (example II). This removes the edge packing effect, however, what happens if there is a PMT problem at the edge of the crystal

                                                                  iv.        CFOV is 75% of the UFOV

                                                                   v.        Relationship of integral differential values: FFOV ≥ UFOV ≥ CFOV

                                                                  vi.        Integral uniformity should be between 1 - 5%. According to NEMA integral uniformity should be ≤ 5% @ 5 million counts

                                                                 vii.        For SPECT intrinsic uniformity should be ≤ 3% and extrinsic floods tend to range a little higher, between 4 - 6%. This may be do to the impurties of the flood source ajnd/or collimator

                                                               

                                                                  ix.        Count profiles can also be drawn by the technologist to further evaluate pixel variation