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A Feasibility Study of a Prototype PET Insert Device to Convert a General-Purpose Animal PET Scanner to Higher Resolution

¹ Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri; ² Institute of Modern Physics, Chinese Academy of Science, Lanzhou, China; ³ Department of Biomedical Engineering, Washington University, St. Louis, Missouri; and ⁴ Department of Electrical and System Engineering, Washington University, St. Louis, Missouri

View larger version (51K): [in this window] [in a new window]   FIGURE 1.  (A) Illustration of microPET F-220 gantry with an insert detector inside the animal port (base cabinet with electronics is not shown). (B) Flood image of high-resolution detector in the insert device with crystal lookup table overlaid on the image.

View larger version (68K): [in this window] [in a new window]   FIGURE 2.  Prototype PET insert device can be mounted to microPET F-220 system after transmission source holder is removed from back of scanner (left). This prototype system consists of a single detector module and a rotation stage (right). Imaging field of view of PET insert device is 4 cm (transverse) by 2–3 cm (axial; see sensitivity section).

View larger version (27K): [in this window] [in a new window]   FIGURE 3.  Calibration for alignment of insert detector with respect to scanner detectors. (A) Reconstructed image of point sources when center-of-rotation error is not corrected. (B) Fit the measured point-source diameter (diameter of half circle in A) as a function of angular offset between insert system and scanner by a straight line; zero-crossing point corresponds to correct angular offset that provides the highest image resolution to PET insert system. In this case, calibrated angular offset is –0.297°, which equals –0.623 times the angle spanned by a single crystal in scanner detector.

View larger version (19K): [in this window] [in a new window]   FIGURE 4.  Composite image of point source measured at different locations (lowest point in image was located at 10 mm below center of field of view of the system). (A) Image from coincidences recorded by detectors in microPET F-220 scanner. (B) Image from coincidences between PET insert detector and detectors in scanner. (C and D) Line profiles through point sources in A and B, respectively.

View larger version (17K): [in this window] [in a new window]   FIGURE 5.  Resolution of PET insert device compared with F-220 scanner. Radial offset of point source was measured along the vertical direction with upper half of field of view having a positive offset. FWHM (A) and FWTM (B) were both measured from horizontal (tangential) and vertical (radial) profiles of point-source images.

View larger version (9K): [in this window] [in a new window]   FIGURE 6.  Sensitivity of PET insert device measured by a 68Ge point source moving along central axis of field of view.

View larger version (19K): [in this window] [in a new window]   FIGURE 7.  A 23.2-g mouse imaged 3 h after injection of 38.5 MBq 18F-fluoride. (A) Images reconstructed by ordered-subset expectation maximization algorithm using coincidences recorded by detectors in microPET F-220 scanner. (B) Images reconstructed by maximum-likelihood expectation maximization algorithm using coincidences between PET insert detector and detectors in scanner.