David A. Weber

Feasibility of dual radionuclide brain imaging with I-123 and Tc-99m.

A study was conducted to evaluate the feasibility of simultaneous dual radionuclide brain imaging with 123I and 99mTc using photopeak image subtraction techniques or offset photopeak image acquisition. The contribution of the photons from one radionuclide to a second radionuclides photopeak energy window (crosstalk) was evaluated for SPECT and planar imaging of a brain phantom containing 123I and 99mTc for a range of activity levels and distribution properties approximating those in rCBF images of the adult human brain. Crosstalk was evaluated for 10% symmetrical energy windows centered on the 123I and 99mTc photopeaks and for 10% energy windows asymmetrically placed to the left and right of the center of the respective photopeaks. Major observations include: (1) in the centered photopeak windows, 99mTc crosstalk in the 123I window is 8.9% of the 99mTc seen in the 99mTc window and ranges from 37.5% to 75.0% of the 123I in the 123I window. 123I crosstalk is 37.8% of the 123I seen in the 123I window and ranges from 4.4% to 8.9% of the 99mTc seen in the 99mTc window; (2) the spatial distribution of a radionuclides crosstalk photons differs from that observed in the radionuclides photopeak window; (3) a 99mTc photopeak window offset to the left does not decrease 123I crosstalk, and the percentage of 99mTc scattered photons is significantly increased in the window.(ABSTRACT TRUNCATED AT 250 WORDS)

Radionuclide skeletal imaging and single photon emission computed tomography in suspected internal derangements of the temporomandibular joint

Fifty one subjects who had pain involving the temporomandibular joint were evaluated using multidirectional tomography, arthrography, conventional nuclear scanning, and single photon emission computed tomography (SPECT) to assess the association of arthritis of the temporomandibular joint with internal derangements related to meniscal dysfunction. Five (56%) of the nine subjects who had normal arthrograms and normal multidirectional tomograms had SPECT scans that were positive for osseous changes. Twenty-two subjects (27 temporomandibular joints) were diagnosed by arthrography to have meniscal displacement with reduction. Multidirectional tomograms of the 27 joints were positive for osseous changes in five (18%) joints, whereas SPECT scans were positive in nine (70%) joints. Twenty subjects (20 temporomandibular joints) had an arthrographic diagnosis of meniscal displacement without reduction. Multidirectional tomograms of the 20 joints were positive for osseous changes in 14 (70%) joints, and SPECT scans were positive in 16 (80%) joints (P less than 0.001 vs control group). Initial observations with SPECT indicate it is a promising imaging method for detecting and staging osseous disease of the TMJ related to meniscal dysfunction.

Calibration for measuring total body nitrogen with a newly upgraded prompt gamma neutron activation facility

A description is given of the calibration and performance of the upgraded facility at Brookhaven National Laboratory (BNL) for measuring total body nitrogen using the technique of prompt gamma neutron activation analysis. With the improved calibration, total body nitrogen can be more accurately measured not only in normal subjects but also in obese and wasted patients. Body hydrogen is used as an internal standard. We examined the effect of a heavy-water premoderator on the uniformity of composite sensitivity, nitrogen and hydrogen measurement statistics, and dose to the subject. The calibration technique corrects the ratio of nitrogen-to-hydrogen counts measured from the subject for body size. Additionally, a correction for subcutaneous adipose tissue on the nitrogen-to-hydrogen count ratio is introduced. The newly upgraded BNL facility provides precision in counting statistics using a Remcal anthropomorphic phantom filled with a tissue-equivalent solution of 2.1% for a body dose of 0.35 mSv using a 2.5 cm D2O premoderator. The measurements were made at five 20 cm sections, counting for 200 s per section.

Bone mineral and body fat measurements by two absorptiometry systems: Comparisons with neutron activation analysis

In 185 adults (68 white and 31 black males, 66 white and 20 black females), total body bone mineral density and content and body fat% were measured by two dual energy X-ray absorptiometry (DXA) systems—Norland XR-26, software version 2.4, and Lunar DPX, software versions 3.4 and 3.6. In a subgroup of 18 males (10 white, 8 black), body fat% and total body calcium were also measured by in vivo neutron activation analysis (IVNA). For total body calcium, the DPX 3.4 system gave the highest (1239 g), IVNA the lowest (1195 g), and the XR-26 (1226 g) was not significantly different from the DPX 3.6 results. For fat%, the XR-26 system gave the highest estimate (23.5%), whereas measurements by the DPX 3.4 and 3.6 systems (17.4 and 18.2%) were similar to the IVNA measurements (18.3%). BMD and BMC measurements by the two DXA systems were highly correlated but significantly different for the entire studied population except in the case of BMC in black males.

Performance of the Delayed- and Prompt-Gamma Neutron Activation Systems at Brookhaven National Laboratory

Brookhaven National Laboratory (BNL) is one of the major facilities pioneering the development of in vivo neutron activation (IVNA) techniques for body composition studies. The IVNA facility at BNL includes a delayed- and prompt-gamma neutron activation system (DGNA and PGNA), as well as an inelastic neutron scattering facility (INS). The BNL DGNA system was first fully established in the 1960’s by Cohn et al. (1969). It is composed of a total-body neutron activation facility (TBNAF) and a whole body counter (WBC), and is used to measure total body sodium, phosphorus, chlorine, and calcium. Body potassium is measured by counting endogenous 40K with the whole body counter. The PGNA system to measure total body nitrogen (TBN) was developed by Vartsky et al. (1979), and the INS system to measure total body carbon (TBC) was instituted by Kehaiyas et al. (1987). The DGNA and PGNA facilities have been upgraded and modified since they were first built.

Improvement of the prompt-gamma neutron activation facility at Brookhaven National Laboratory

The prompt-gamma neutron activation facility at Brookhaven National Laboratory was upgraded to improve both the precision and accuracy of its in vivo determinations of total body nitrogen. The upgrade, guided by Monte Carlo simulations, involved elongating and modifying the source collimator and its shielding, repositioning the systems two NaI(Tl) detectors, and improving the neutron and gamma shielding of these detectors. The new source collimator has a graphite reflector around the 238PuBe neutron source to enhance the low-energy region of the neutron spectrum incident on the patient. The gamma detectors have been relocated from positions close to the upward-emerging collimated neutron beam to positions close to and at the sides of the patient. These modifications substantially reduced spurious counts resulting from the capture of small-angle scattered neutrons in the NaI detectors. The pile-up background under the 10.8 MeV 14N(n, gamma)15N spectral peak has been reduced so that the nitrogen peak-to-background ratio has been increased by a factor of 2.8. The resulting reduction in the coefficient of variation of the total body nitrogen measurements from 3% to 2.2% has improved the statistical significance of the results possible for any given number of patient measurements. The new system also has a more uniform composite sensitivity.

A high-resolution SPECT system based on a microchannel-plate imager

The authors have developed a high-resolution single-photon emission computed tomography (SPECT) system for small-animal studies with /sup 125/I. The SPECT camera uses a Hamamatsu microchannel-plate imager PIAS (photon-counting image acquisition system), a 0.7-mm-thick NaI(Tl) plate, and a lead-glass parallel-hole collimator. The 15-mm-diameter field of view (FOV) of the PIAS tube was enlarged by an optical fiber faceplate taper to provide a 26-mm camera FOV. Camera absolute sensitivity (counts detected/gamma photons emitted) is 2*10/sup -5/ for /sup 125/I. The system provides an in-plane resolution of about 0.7 mm FWHM (full width at half maximum) in the reconstructed image for a 15-mm radius of rotation. SPECT images from phantom studies and from organs in the rat and mouse provide examples of the resolving capacity of the system. >

Kinetics and Imaging Characteristics of 99mTc-Labeled Complexes Used for Bone Imaging1

Activity levels of 99TC-labeled compounds, 18F, and 85Sr were obtained at 1, 3, and 5 hr. postinjection in normal and healing fractured bone and in soft-tissue rat specimens. Serial diagnostic bone images and blood and urine kinetics were obtained in patients with each of the TC-labeled compounds. Computer-processed images were used to evaluate in vivo kinetics. 99mTC pyrophosphate provides the best overall characteristics for bone imaging. Improved quality and bioassay procedures are required, however, before any one agent can be designated the radiopharmaceutical of choice for diagnostic bone imaging.

Calibration of the delayed‐gamma neutron activation facility

The delayed-gamma neutron activation facility at Brookhaven National Laboratory was originally calibrated using an anthropomorphic hollow phantom filled with solutions containing predetermined amounts of Ca. However, 99% of the total Ca in the human body is not homogeneously distributed but contained within the skeleton. Recently, an artificial skeleton was designed, constructed, and placed in a bottle phantom to better represent the Ca distribution in the human body. Neutron activation measurements of an anthropomorphic and a bottle (with no skeleton) phantom demonstrate that the difference in size and shape between the two phantoms changes the total body calcium results by less than 1%. To test the artificial skeleton, two small polyethylene jerry-can phantoms were made, one with a femur from a cadaver and one with an artificial bone in exactly the same geometry. The femur was ashed following the neutron activation measurements for chemical analysis of Ca. Results indicate that the artificial bone closely simulates the real bone in neutron activation analysis and provides accurate calibration for Ca measurements. Therefore, the calibration of the delayed-gamma neutron activation system is now based on the new bottle phantom containing an artificial skeleton. This change has improved the accuracy of measurement for total body calcium. Also, the simple geometry of this phantom and the artificial skeleton allows us to simulate the neutron activation process using a Monte Carlo code, which enables us to calibrate the system for human subjects larger and smaller than the phantoms used as standards.

High resolution pinhole SPECT for tumor imaging

High-resolution, non-invasive, 3D-imaging techniques would greatly benefit the investigation of the localization properties of tumor-specific radiopharmaceuticals in laboratory animals. The present study reports how pinhole SPECT can be applied to tumor localization studies in small laboratory animals to provide high resolution SPECT images in vivo. Pinhole SPECT was performed using a rotating scintillation camera, equipped with a pinhole collimator. The sensitivity of a 2 mm diameter collimator at 45 mm from the source is 90 cps/MBq for 99mTc. The planar spatial resolution at a 45 mm distance is 2.2 mm. The transaxial spatial resolution, with a distance of 45 mm between the collimator aperture and the axis of rotation, is 3.1 mm. For SPECT imaging, spatial linearity is preserved across the usable field-of-view. The major advantage of the high resolution properties of pinhole tomography is demonstrated by the enhanced lesion-to-normal-brain uptake ratio achieved on tomographic slices as compared to planar images. For example, 201Tl tumor-to-normal-brain uptake ratios of 1.1 to 1.3 observed on planar images, corresponded to ratios ranging from 3.2 to 3.7 on the SPECT slices. Examples of the activity distributions of two radiopharmaceuticals in tumor and in normal brain for sagittal and coronal images are given. In all cases, tumors are clearly delineated on the pinhole SPECT slices. The present study shows that pinhole SPECT performed with standard SPECT instrumentation can give high spatial resolution images, with a FWHM approximately 3 mm and a sensitivity approximately 100 cps/MBq for 99mTc.