Jerold W. Wallis

Three-dimensional display in nuclear medicine

Several surface and volume rendering techniques are compared using nuclear medicine data including several new methods developed by the authors specifically for scintigraphic data. The techniques examined are summed projection, thresholded projection, threshold-based surface illumination, volumetric compositing, maximum-activity projection, sun-weighted maximum-activity projection, and variable attenuation. The advantages and disadvantages of each method are discussed in relation to the goals of three-dimensional display, which are defined herein. Selected images are shown to illustrate the usefulness of the methods.

An optimal rotator for iterative reconstruction

For implementations of iterative reconstruction algorithms that rotate the image matrix, the characteristics of the rotator may affect the reconstruction quality. Desirable qualities for the rotator include: (1) preservation of global and local image counts; (2) accurate count positioning; (3) a uniform and predictable amount of blurring due to the rotation. A new rotation method for iterative reconstruction is proposed which employs Gaussian interpolation. This method was compared to standard rotation techniques and is shown to be superior to standard techniques when measured by these qualities. The computational cost was demonstrated to be only slightly more than bilinear interpolation.

Fetal Radiation Dose from 18F-FDG in Pregnant Patients Imaged with PET, PET/CT, and PET/MR

The fetal radiation dose from 18F-FDG was estimated in a series of pregnant women who underwent a PET scan during a clinical workup for malignancies. Methods: Six pregnant patients were injected with 18F-FDG (activity range, 296–385 MBq). Three patients were scanned during the first trimester (1 with PET and 2 with PET/CT), 2 were scanned during the second trimester (with PET/MR imaging), and 1 was scanned during the third trimester (with PET). The time-integrated activity coefficients were derived from the fetal radioactivity concentrations measured on the images for all but 1 patient (in early pregnancy [5 wk]), in whom the activity in the uterus was used as a proxy. The coefficients of the mother’s organs were derived from standard values (from the International Commission on Radiological Protection). Results: Fetal doses ranged from 6.29E–03 to 2.46E–02 mGy/MBq. An earlier bladder voiding reduced these doses by 25%–45%. The 2 patients who underwent PET/MR imaging—in whom fetal contours could be accurately delineated—displayed the lowest fetal absorbed dose, likely because of more accurate region drawing, with the inclusion of areas of both low and high fetal uptake. Moreover, PET/MR imaging did not necessitate additional radiation for attenuation correction. The placenta, delineated on a PET/MR imaging scan, concentrated 0.27% of the injected activity. Conclusion: Fetal radiation doses are higher in early pregnancy than in late pregnancy, and there can be considerable intersubject variability. However, the total absorbed dose is always well below the threshold for noncancer health effects throughout pregnancy. PET/MR imaging is the optimal PET procedure for imaging pregnant women because it is not associated with radiation for attenuation correction and allows more accurate dosimetric calculations.

99Tcm-MDP uptake by lymph nodes following tracer infiltration: clinical and laboratory evaluation

Uptake of bone scanning agents in non-osseous sites has been described in a variety of pathologic conditions including tumor metastases. We have seen several patients in which such uptake was proximal and ipsilateral to the injection site of 99Tcm-methylene diphosphonate, apparently in normal lymph nodes. To further investigate this phenomenon, it was studied in a rat model. Activity in popliteal nodes ipsilateral to the injection site was over 60-fold greater in the animals that received subcutaneous (s.q.) footpad injection compared to femoral IV injection. Ipsilateral popliteal node activity in the s.q. group was 159 times that of contralateral popliteal nodes, with an ipsilateral node to liver ratio of 184:1. In summary, dramatically increased uptake of 99Tcm-MDP in normal lymph nodes ipsilateral and proximal to an extravasated injection has been demonstrated. An awareness of this phenomenon in the clinical setting can avoid confusion with pathologic forms of soft tissue uptake.

Use of the internet for teaching in nuclear medicine

The Internet provides several new capabilities for education in nuclear medicine, including learning at a distance, facilitation of collaboration, increased availability of training resources, and ability to develop interactive teaching materials. Dedicated case-authoring software aided development of digital teaching files at the Mallinckrodt Institute of Radiology and the Joint Program in Nuclear Medicine. Accesses to these two teaching files from sites around the world have grown rapidly. Improvements in the speed of the Internet will allow inclusion of more images at higher resolution and more extensive use of cine. Development of server-based software will allow simulation of the actual image-reading environment. A better understanding of how to use this new media will spur continued expansion in use of the Internet for nuclear medical education.

Massively parallel computers for 3D single-photon-emission computed tomography

Since the introduction of the expectation-maximization (EM) algorithm for generating maximum-likelihood (ML) and maximum a posteriori (MAP) estimates in emission tomography, there have been many investigators applying the ML method. However, almost all of the previous work has been restricted to two-dimensional (2D) reconstructions. The major focus and contribution of this paper is to demonstrate a fully three-dimensional (3D) implementation of the MAP method for single-photon-emission computed tomography (SPECT). The 3D reconstruction exhibits an improvement in resolution when compared to the generation of the series of separate 2D slice reconstructions. As has been noted, the iterative EM algorithm for 2D reconstruction is highly computational; the 3D algorithm is far worse. To accommodate the computational complexity, we have extended our previous work in the 2D arena and demonstrate an implementation on the class of massively parallel processors of the 3D algorithm. Using a 16000 processor MasPar machine, the algorithm is demonstrated to execute at 1.24 s/EM iteration for the entire 64 x 64 x 64 cube of 64 planar measurements obtained from the Siemens Orbiter rotating camera operating in the high-resolution mode.

Immunoscintigraphy with a new indium-111-labeled monoclonal antibody (MAb 1A3) in patients with colorectal cancer

PURPOSE: This study was designed to evaluate a new anticolorectal carcinoma monoclonal antibody (1A3), conjugated with the bifunctional chelating agentN,N′-bis(2-hydroxybenzyl) 1 (4-bromoacetamidobenzyl) 1,2-ethylenediamine-N,N′-diacetic acid and labeled with indium-111, in a Phase I/II study involving 38 patients with localized or advanced colorectal cancer. METHODS: Patients were injected with indium-111-N,N′-bis(2-hydroxybenzyl) 1 (4-bromoacetamidobenzyl) 1,2-ethylenediamine-N, N′-diacetic acid-monoclonal antibody 1A3 (1–50 mg, 1–5 mCi) and imaged at two or three sessions one to five days later. Scintigraphic findings were compared with radiologic, pathologic, surgical, and other clinical findings to assess the accuracy of radioimmunoscintigraphy. RESULTS: At least one known tumor site was clearly defined by planar scintigraphy in 29 (76 percent) patients. Increased radioactivity was seen in 40 of 63 known tumor sites (37/43 abdominal-pelvic, 3/15 hepatic, and 0/5 pulmonary sites) without any apparent dose-related effects. Nineteen previously undetected sites were considered positive by imaging, and, of these, six were biopsy-proven tumor sites, four were probable tumor sites, three were definitely false positive sites, and six were probable false positive sites. Radioimmunoscintigraphy detected proven tumor in 15 of 16 patients with negative or equivocal computed tomography results. Of the 28 patients with rectosigmoid cancer, 25 (89 percent) had positive studies with 34 of 47 tumor sites showing definite uptake on the scintigrams. This included 3 of 9 hepatic metastases. The only adverse reaction occurred in one patient who developed transient hives. Human anti-mouse antibody responses occurred in approximately one-half of the patients injected with doses of 10 or 50 mg. CONCLUSION: This study shows that radioimmunoscintigraphy with this indium-111-labeled monoclonal antibody is safe, it can detect most nonhepatic abdominalpelvic tumors with a positive predictive value of 83 (44/ 53) percent, and it should prove to be useful, particularly in the diagnosis of recurrent rectal carcinoma.

Interactive reconstruction in single-photon tomography

A new method is described to allow interactive selection of the reconstruction filter at the time of interpretation of images from single-photon tomography. In the filtered back projection algorithm, the only part of the reconstruction process requiring user interaction is the selection of the window function. Since the ramp and window filters have different purposes, they can be separated, placing the window at the end of the reconstruction process as a three-dimensional filter. All stages of reconstruction except the window filtering are performed before the physician begins to interpret the study. The three-dimensional filtering is performed very rapidly with use of the Chebyshev convolution algorithm. A 64×64×64 pixel cube of data is filtered in 13–33 s using filters of 3–11 lengths. Smaller volumes of image data can be filtered in less than 1 s; thus, the user can interactively choose any desired filter for a given tomographic study at the time of interpretation of the images.

ABNM Position Statement: Nuclear Medicine Professional Competency and Scope of Practice

The purpose of this position statement is to define the scope of nuclear medicine practice and the professional competencies required now and for the future. Medical practice will change dramatically over the coming decades in ways no one can predict. The methodologies, technology, and radiotracers will certainly change. However, the core concepts and knowledge that were first required for nuclear medicine board certification in 1971 still hold true and will guide and sustain us into the future. The American Board of Nuclear Medicine (ABNM) is one of the 24 primary boards of the American Board of Medical Specialties (ABMS). This organizational structure provides an infrastructure that promotes transparency and accountability for all the member boards.

Use of the selective linogram in cardiac tomography quality control.

BackgroundQuality control for detection of patient motion is essential in tomographic myocardial imaging. Despite significant limitations, the summation image or conventional “linogram” has long been advocated as a useful image in the detection of vertical motion. In this study a new quality control image entitled the “selective linogram” is proposed to replace the summation image in routine cardiac single-photon emission cardiac tomography (SPECT) quality control. The selective linogram is constructed in a manner somewhat analogous to the sinogram. In the sinogram, each row represents a different projection angle; in the selective linogram each column represents a different projection angle.Methods and ResultsAfter selection of eight motion-free studies from acquisitions at our clinical center, vertical motion of various types (bounces, shifts, and creep) were added to the projection frames. Summation image and selective linogram quality control images from these motion-containing studies and the original motion-free studies were presented in a blinded manner to two observers for scoring of patient motion. The selective linogram was significantly more accurate in allowing detection of vertical motion than was the summation image (accuracy 89% vs 47%).ConclusionsThe selective linogram image is markedly superior to the summation image for the detection of vertical patient motion during cardiac SPECT. This new technique can be a valuable aid in SPECT quality control.