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M Dahlbom

Publications and source records attributed to M Dahlbom.

13 recordsLinked to original sources
PubMed1992

The role of positron emission tomography in oncology and other whole-body applications.

Imaging and quantifying biochemical and physiological processes with PET clearly has major potential significance for all organ systems and many disease states. Although the full utility and potential of emerging new applications of PET in organs other than the heart and brain must be demonstrated in basic and clinical research studies, the rapidly accumulating aggregate experience in oncology in particular, and in other organ systems and disease states as well, indicates that PET is now truly becoming a modality of both clinical and investigative use for the body as a whole as well as for specific organ systems. Whole-body PET FDG imaging (Fig 9) illustrates the potential of biochemical imaging to map the distribution of cancer throughout the body. With the growing list of radiopharmaceutical and quantitative techniques applicable to cancer studies with PET, this field will continue to realize significant growth.

Humans↗
PubMed1992

Evaluation of a 3D reconstruction algorithm for multi-slice PET scanners.

A fully 3D reconstruction algorithm based on filtered backprojection was evaluated for the reconstruction of data obtained with multi-slice positron emission tomography (PET) scanners which have had the septa removed. This algorithm uses forward-projection through the reconstructed images of a 2D subset of the data to complete the 3D dataset thus satisfying the condition of shift invariance. This is followed by 3D filtered backprojection. Axial sampling was doubled by combining adjacent polar angles, thus improving reconstructed axial resolution. The algorithm was tested using real and simulated datasets and gave high quality reconstructions without artifacts over a wide range of imaging conditions. Events are placed accurately throughout the imaging volume as determined by measurements with a MRI/PET registration phantom. The forward-projection step leads to degradation in image resolution due to insufficient axial and transaxial sampling. This effect is amplified if multiple iterations of the algorithm are used, with little decrease in image noise. Changing the filter employed in the initial 2D reconstruction can be used to alter the noise and resolution characteristics of the 3D images. This algorithm has proved very robust at reconstructing 3D PET data and is relatively fast. Those small problems which exist can be attributed to detector sampling problems, especially in the axial direction, which is a consequence of the geometry of these scanners, which are designed primarily for 2D data acquisition.

Algorithms↗
PubMed1992

The application of positron emission tomographic imaging with fluorodeoxyglucose to the evaluation of breast disease.

Positron emission tomography (PET) is a computer-aided tomographic imaging technique that uses positron-emitting compounds to trace biochemical processes of tissue, and construct images based on them. The authors applied a whole-body PET imaging technique to patients with breast masses or mammographic abnormalities using the isotope 2-[F-18]-fluoro-2-deoxy-D-glucose (FDG), in a clinical trial to evaluate the feasibility of using PET to identify primary breast cancer, axillary lymph node involvement, and systemic metastases, before surgical resection. Fourteen patients have been entered on this study, 10 of whom proved to have breast cancer. Positron emission tomography correctly predicted the nature of 12 of the 14 primary breast lesions, and correctly determined the lymph node status of 11 of the 14 patients. The authors conclude that PET with FDG has potential as a diagnostic modality for detection of primary breast cancer, particularly in the patient with radiodense breasts by conventional mammography, and that it has potential for the preoperative identification of axillary lymph node metastases.

Adolescent↗
PubMed1992

Evaluation of the skeletal kinetics of fluorine-18-fluoride ion with PET.

To evaluate the feasibility of quantitatively assessing regional skeletal fluoride uptake in humans in focal and generalized bone disease, we investigated the skeletal kinetics of [18F]fluoride ion with dynamic PET imaging. Dynamic image sets were acquired over a 60-min interval in a multiplane PET device, and input functions (plasma 18F time-activity curves) were measured directly from arterialized blood and, in some cases, determined from image-derived left ventricular cavity activity measurements. Our results indicate: 1. A steady-state ratio of [18F]fluoride ion concentration in plasma to whole blood greater than unity (1.23 for plasma to directly assayed whole blood and 1.44 for plasma to left ventricular cavity imaged concentrations. This concentration difference produces a scaling factor that must be considered when using image derived or directly measured input functions. 2. The preferred tracer kinetic model configuration for [18F]fluoride ion skeletal kinetics is a three compartment model that includes a "bound" and "unbound" bone [18F]fluoride ion compartment. 3. The rate constant for forward transport of [18F]fluoride ion from plasma to the extravascular space of bone (K1) and the regional blood volume parameter generate estimates of bone blood flow and vascular volume, respectively, that are in the physiologic range of reported for mammals. Estimates of the uptake constant for fluoride in bone, using nonlinear regression (KNLR = 0.0360 +/- 0.0064 ml/min/ml), are in very good agreement with an estimate of the same parameter obtained with Patlak graphical analysis (KPAT = 0.0355 +/- 0.0061 ml/min/ml). 4. Generating parametric images of KPAT facilitates quantification of regional bone [18F]fluoride ion kinetics. The method is computationally practical, and, with either the parametric imaging approach or with standard region of interest analysis, can be used to generate quantitative estimates of fluoride uptake (a "bone metabolic index") in focal skeletal regions or in more generalized distributions.

Adult↗
PubMed1992

Whole-body positron emission tomography: Part I. Methods and performance characteristics.

Methods for whole-body PET imaging have been developed to provide a clinical tool for the detection and evaluation of primary and metastatic cancers. The axial FOV of the PET system is extended by imaging at multiple bed positions to cover the whole body. In typical rectilinear PET scans, only a small fraction of the data is collected to form two-dimensional projection images. In this work, 100% of the projection data was collected to form the two-dimensional projection images. These projection images were generated for continuous angles over 180 degrees by resorting sinogram data. In addition, tomographic images were formed by using filtered backprojection reconstruction without attenuation correction. Coronal and sagittal cuts were then extracted from the three-dimensional data set. The tomographic images were reconstructed to a resolution of 10.8 mm in all dimensions because of statistical limitations of the data. Both methods of image formation resulted in images of high quality with the tomographic reconstruction providing the highest contrast and resolution. An acquisition time of 1-2 min/bed position after a 10-mCi injection of [18F]fluoride ion or [18F]FDG was found to give a sufficient number of counts for producing images of good resolution and contrast, from a total scanning time of 32-64 min.

Deoxyglucose↗
PubMed1990

Positron emission tomography--a new technique for studies of the central nervous system.

Positron emission tomography (PET) has become an important tool to study the central nervous system. Examples of such studies are cerebral blood flow and metabolism and determination of receptor characteristics of the brain. In the following the basic principles and the physics behind PET are given. Different aspects are discussed such as detector design, image reconstructions and data analyses. Since quantification is essential in PET, data have to be corrected for absorption, scatter and random coincidences. These corrections and their influence on image data are discussed. A review of state-of-the-art PET research of the brain is given.

Brain↗
PubMed1989

A preliminary evaluation of the Scanditronix PC2048-15B brain scanner.

The PC2048-15B is the brain version of the new generation of Scanditronix positron camera systems. It is based on a detection unit with 16 scintillating crystals mounted on 2 dual photomultiplier tubes. A system description is given and preliminary test results including spatial resolution, sensitivity to true and random coincidences, scatter correction, and count rate linearity are presented.

Brain↗
PubMed1989

Scatter fraction: measurement and correction.

The concept of scatter in Positron Emission Tomography is reviewed regarding origin and influence on data. Different ways to measure and correct for scatter are discussed.

Scattering, Radiation↗
PubMed1989

The C15O2 build-up technique to measure regional cerebral blood flow and volume of distribution of water.

A new method to measure regional CBF (rCBF) and volume of distribution of water is presented. It centres on recording the tissue build-up and retention of 15O-labelled water during the continuous inhalation of 15O-labelled carbon dioxide. Simultaneously, the arterial concentration is continuously monitored, and corrections for delay and dispersion in the recorded response are made by curve fitting. The values for the volume of distribution of water obtained in four normal subjects were close to reported in vitro values. Using the same fixed distribution volumes for both build-up and steady-state studies resulted in comparable rCBF values for both techniques.

Adult↗
PubMed1988

Validation of PET-acquired input functions for cardiac studies.

To validate the determination of the arterial input function by noninvasive dynamic PET imaging, measurements of blood-pool activity in canine LV by PET were compared to beta probe measurements of arterial blood withdrawn directly from the LV. PET scans were done during intravenous bolus injections of [13N]ammonia or 82Rb, while the activity of blood withdrawn continuously from a catheter inserted in the LV was measured with a beta probe. PET determinations of LV blood-pool activity were compared with dispersion-corrected beta probe time-activity curves. In 15 experiments involving four dogs under a wide range of physiologic conditions, LV time-activity curves obtained with PET matched well in shape with those obtained with the beta probe. Linear regression yielded slopes within 10% of unity (95% confidence interval) and high correlation (r greater than 0.968, p less than 0.001). We conclude that noninvasive measurement of the arterial input function by dynamic PET imaging is valid.

Ammonia↗
PubMedDate not supplied

3D PET using a conventional multislice tomograph without septa.

A conventional multislice positron emission tomography scanner was modified to operate without interplane septa to evaluate its performance in collecting and reconstructing data in a three-dimensional (3D) format, thereby significantly increasing system sensitivity. A 3D filtered backprojection algorithm was implemented and tested, using both computer simulations and phantom measurements. No artifacts were apparent in the test images, although the algorithm was shown to lead to a 11% degradation in transaxial resolution in the outer planes. Following septa removal, sensitivity was found to increase by a factor of 7 with an increase in scatter fraction from 16 to 41%. Axial resolution degraded from 6.9 to 7.7 mm full width at half maximum at the center of the field of view. The maximum count rate without septa was 2.4 x 10(5) cps, at a concentration of 0.4 microCi/ml, compared with 1.3 x 10(5) cps at 1.5 microCi/ml with septa. Brain studies were performed with volunteers using 18F-fluorodeoxyglucose, 18F-fluorodopa, and H2 15O to compare noise-equivalent count rates and qualitatively assess image quality over a wide range of imaging conditions.

Algorithms↗
PubMedDate not supplied

Geometric mispositioning in positron emission tomography.

The phenomenon of geometric mispositioning (defined as having a geometric proper plus a parallax component) was studied and characterized on Neuro- and whole body PET systems employing 2-D modular detectors (CTI/Siemens ECAT-831/08 and 931/08) as well as an older system (CTI ECAT-911). Measurements taken with precisely spaced line sources showed image distortions of objects away from the center of the field of view (FOV), with global mispositionings of -1.4, 1.5 and 14 mm (931 and 911), and -0.5, 10 mm (831) at 10, 20 and 30 cm (931 and 911) and 10, 20 cm (831) from the center of the FOV. Structures as close as 5 cm (931/911) or 4 cm (831) to the center of the FOV are mispositioned by more than 1 mm. This is clearly inacceptable in cases where accurate correlation of PET and NMR images is needed to acquire anatomical information in neurological studies, or when gated cardiac studies are performed in order to precisely determine myocardial wall thickness. A fast, on-line geometric correction was performed by creating new, uniformly spaced sinograms to be mapped to the original sinograms. Geometric mispositioning was mathematically derived, while parallax mispositioning was estimated by a linear fit of the data partially corrected for sampling non-uniformity. Our correction technique can be easily tailored to any PET system available on the market.

Mathematics↗