Slide 1:PET Instrumentation Presented by: Group 4 Alex Ramos Beatriz Pelaez Gipsy Morales Meylen Reyes


OBJECTIVES :OBJECTIVES Describe how PET reconstruction can be performed with a variety of algorithms Describe the process of displaying data for the physician. Discuss the implication of image fusion Describe the PET/CT scanner Discuss Attenuation Correction by transmission imaging Advantages of combined PET/CT scanners Discuss scanner calibrations Explain Quantitative Image Information Discuss Radiation safety in PET


RECONSTRUCTIONALGORITHMS :RECONSTRUCTIONALGORITHMS The LORS are store during data acquisition Raw data must first be reformatted Each sinogram represents one image slice


PET Reconstruction :PET Reconstruction Filtered back projection (FBP) Ordered subset expectation maximization (OSEM) Row-action maximum likelihood algorithm (RAMLA)


FILTERED BACK PROJECTION (FBP) :FILTERED BACK PROJECTION (FBP) Reconstructing images of objects spirally Scanned with two-dimensional detectors with a novel algorithm under a variable pitch (non-constant speed), Where the object is not restricted to moving at a constant velocity.


FILTERED BACK PROJECTION (FBP) :FILTERED BACK PROJECTION (FBP)


Ordered Subset Expectation Maximization (OSEM) :Ordered Subset Expectation Maximization (OSEM) It can be used to reconstruct studies acquired in any matrix size over any number of angles with a parallel hole or fanbeam collimator. The program can reconstruct data acquired from cameras with 1, 2 or 3 heads.


Ordered Subset Expectation Maximization (OSEM) :Ordered Subset Expectation Maximization (OSEM)


Row-action Maximum Likelihood Algorithm (RAMLA) :Row-action Maximum Likelihood Algorithm (RAMLA) Provides similar results to OSEM Require sequences of orthogonal projections Faster than OSEM


ITERATIVE RECONSTRUCTION ALGORITHMS :ITERATIVE RECONSTRUCTION ALGORITHMS Estimates the image values and serially update those estimates by repeated calculations Very high quality, high-resolution images


ITERATIVE RECONSTRUCTION ALGORITHMS :ITERATIVE RECONSTRUCTION ALGORITHMS


Attenuation Correction :Attenuation Correction Accurate distribution of a radiotracer Complex mixture of tissues each with a different effect on photon attenuation lung tissue


Attenuation Correction :Attenuation Correction 5-10 mCi of Ge68 or Cs137 –source rod Data is reconstructed into attenuation correction maps Important to understand: Attenuation corrected images show the correct amounts of radioactivity in the body


Slide 14:Figure A: The gamma camera cannot distinguish increased counts Figure B: Demonstrates artificial increased counts in lung and decreased counts in heart A. B.


Attenuation Process :Attenuation Process Attenuation coefficients Very different between each type of tissue or organ Image segmentation Selecting image regions for various types of tissues or organs Known attenuation Coefficients Can be preset depending on the type of tissue or organ.


Slide 16:Full history 57-year-old woman Recently diagnosed non-small cell lung cancer FDG-PET was requested for initial staging Radiopharmaceutical 12.3 mCi F18 Flurodeoxyglucose (FDG) i.v. Findings large right lower lobe mass with central necrosis, consistent with the patient's known lung cancer. Example Study A. Transmission Scan B. Attenuation Corrected Scan A. B.


Slide 17:(Non-attenuation corrected images) (Attenuation corrected images)


Importance of Attenuation Correction/Patient Prep :Importance of Attenuation Correction/Patient Prep Attenuation correction and patient prep are important factors in image quality


PET/CT Hybrid Scanners :PET/CT Hybrid Scanners Two Advantages Physiological (PET) is aligned with high resolution images of the anatomy (CT) CT imaging is very fast CT is able to be used for attenuation correction Diagnostic CT- High Resolution


PET/CT Fusion :PET/CT Fusion Transaxial PET (“A”) and Fused PET/CT (“B”)


Scanner Calibrations :Scanner Calibrations Two type of scanner calibrations Characterization(Operational) calibrations Those that are fundamental to the operation of the PET scanner Correctional calibrations Those that need compensation for usual variations


Characteristic Calibrations :Characteristic Calibrations Energy Window Calibrations How? BGO energy resolution is relatively poor, the energy window may be set from 300 keV to 650 keV When? Quarterly ,by the technologist on some systems and a service engineer on others. Gain Settings How? Sensitivity response from the individual detectors and modules are maintained. A radioactive rod is used, requires a high number of events so many minutes may be taken up. When? Weekly and even Daily, depending on the amount of use.


Characteristic Calibrations :Characteristic Calibrations Coincidence Timing How? Adjusts for the timing differences in the event detection circuitry Blank Scan How? Used as a uniformity reference. In some respects the blank scan may be thought of as viewing a daily uniformity flood image on a scintillation camera. When? Daily. Important to know: Patient data that is archived should have that day’s blank scan data for reference in case future reconstruction is required


Correction Calibrations :Correction Calibrations Normalization How? Rotating rod sources with low activity, and acquiring data that will be used to balance the efficiency of all detectors in the scanner It is much like a high-count uniformity correction in a scintillation camera When? Quarterly, or after a major service. May take from 6 to 24 hours to complete. Absolute activity How? Taking a precisely known amount of activity and loading a water-filled phantom whose volume is accurately known. It allows the conversion of a patient scan into a representation of the percentage of injected dose per volume or gram of tissue. When? Quarterly, or after a major service, after all other calibrations are done.


Quantitative Image Information :Quantitative Image Information In tumors can be measured to differentiate between malignant and benign tissue SUV can be useful in the measuring of the tumor Well counter calibration allows the conversion of the image They are based on either on the injected activity per patient weight (Kg) or per body surface area (m2)


SUVs :SUVs Measurements may be mCi or mBq Body surface area is calculated in the following manner: BSA (m2)= (weight in kg)0.425 X (height in cm)0.725 X 0.007184 Determined by placing ROI over tumor and using computer programs to automatically calculate the value Change with time 2.5 or greater differentiates benign from malignant lung lesions


DISPLAYING PET DATA :DISPLAYING PET DATA Data acquisition is substantially different in PET than it is in planar nuclear medicine and SPECT. There is an entirely different set of definitions and considerations. The PET computer system creates image data


Slide 28:DISPLAYING PET DATA


Image Fusion :Image Fusion In the early 1900’s CT or MRI → the exact site of anatomy PET or SPECT →physiological information Image fusion software: import DICOM slice information from CT, MRI, SPECT or PET


Color Fusion :Color Fusion


Image Fusion :Image Fusion Focus Fusion: uses a proprietary image processing algorithm developed by Able Software to eliminate the problems of limited depth of field and combining them into a single fully-focused, high resolution image


Fusion Command :Fusion Command


Plane Fusion :Plane Fusion


PET/CT Scanners :PET/CT Scanners *The best device for image fusion*


PET/CT Scanners :PET/CT Scanners Purposes of CT scan Provide a perfectly aligned anatomic image Transform into an attenuation map for correcting the PET images


Color Fusion of CT and PET Images :Color Fusion of CT and PET Images


Radiation Safety in PET :Radiation Safety in PET Technologists performing PET have a higher radiation exposure The patient emits many Compton-scattered-photons Their mean energy is in the range of 200 to 300 keV PET uses the application of time, distance and shielding to maintain (ALARA)


Radiation Safety in PET :Radiation Safety in PET Syringe Shields Waste containers Laboratory bench Exposure form patient 1mR/hr at 1m


Questions :Questions True/False The CT scan may be transformed into an attenuation map for correcting the PET images. The best device for image fusion is one that contains both a PET and CT scanner into one gantry. 3. Attenuation coefficients are heterogeneous within the brain and liver. 4. Iterative methods are techniques that sequentially refine estimated pixel values and provide more accurate reconstruction of the radiotracer’s distribution in the body. Short Answer 5.Name two advantages of Computerized Tomography. 6. Why do activity edges occur in non-attenuation?


Question :Question Short Answer 7.List 4 types of Image Fusion 8.What is the amount of SUV needed to differentiate benign from malignant lesions? 9. What is the mean energy of Compton scattered photons that patient emit? 10.Which of the following algorithms are use in PET reconstruction.  a.  FBP, OSEM  b. RAMLA, OSEM    c. FBP, RAMLA and OSEM  d. None of the above


ANSWERS :ANSWERS True True False True Diagnostic and Attenuation Correction Due to the decreased attenuation of the skin Color, Focus, Fusion and Plane 2.5 200 to 300 keV C (FBP, RAMLA and OSEM)


References :References Christian, . Waterstram-Rich, Paul E. Kristen M (2007). Nuclear Medicine and Pet/CT . St. Louis, Missouri: Mosby Elsevier. Davis, Bernard E Textbook of Microbiology. NY: Hoeber Medical DivisionHarper & Row Publishers. Singer, Underwood, Charles Joseph, Edgar Ashworth (1962). A Short History of Medicine. NY, and Oxford: Oxford Univ. Press.