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D L Bailey

Publications and source records attributed to D L Bailey.

At least 19 recordsLinked to original sources
PubMed1992

3D acquisition and reconstruction in positron emission tomography.

3D positron emission tomography (PET) refers to an acquisition geometry and reconstruction procedure that allows all coincidence events within the solid angle of the tomograph to be recorded and subsequently reconstructed. The reconstruction algorithm must consider the angle of each coincidence event relative to the central axis of the scanner. The aim of the technique is to maximise the sensitivity of the system by utilising all events that it is possible to record from the object. Conventional cylindrical 2D PET systems typically detect approximately 0.4%-0.5% of decaying nuclei within the field of view; with a 3D system this can increase to over 3%. Reconstruction in 3D using filtered-backprojection techniques has been developed and provides results that show little degradation of physical characteristics compared with 2D systems, apart from an increased scatter event rate. 3D techniques may be used to (i) improve data quality using currently acceptable doses of radioactivity and scanning times; (ii) extend the scanning period for short-lived tracers, especially 11C-labeled ligands; or, conversely (iii) decrease injected doses of radiotracer or reduce scanning times to achieve similar results as those using current methods in 2D.

Humans↗
PubMed1992

Physical performance of a positron tomograph for brain imaging with retractable septa.

Performance characteristics of a new design of positron tomograph with automatically retractable septa for brain imaging have been studied. The device, consisting of block BGO detectors (8 x 8 elements per block), has a ring diameter of 76 cm and an axial FOV of 106.5 mm. The in-plane resolution is on average 5.8 mm and 5.0 mm (FWHM) for stationary and wobble sampling, respectively, over the central 18 cm of the transaxial FOV. Its unique feature is the capability of data acquisition both in the 'conventional' 2D mode (with septa) or 3D mode (septa retracted) where coincidences between any of the 16 detector rings are acquired. When scattered events are subtracted, the efficiency for a 20 cm diameter uniform cylinder increases overall by a factor of 4.8 between 2D (septa extended) and 3D modes. For a 20 cm phantom the trues/singles ratio is higher for 3D than for 2D but for a given unscattered trues rate, the randoms rate in 3D is higher. At 380 keV the scatter fraction within a 20 cm cylinder is 10% (septa extended) and 36% (retracted). In spite of the increase in scatter when septa are retracted, the increased efficiency in the 3D mode of acquisition yields distinct advantages, particularly in the many studies where tracer concentration is low and consequently where dead time and random rates are less important.

Brain↗
PubMed1991

A method for measuring the absolute sensitivity of positron emission tomographic scanners.

A need exists to measure the absolute sensitivity of a positron emission tomographic (PET) scanner in units of counts.s-1.MBq-1. At present sensitivity is generally determined by measurement of a radionuclide of known concentration distributed in a water-filled cylindrical phantom, usually 20 cm in diameter. The measurement is confounded by self-attenuation of the source and scatter within the cylinder and does not give a true absolute sensitivity measurement. Due to variations in the magnitude and treatment of these factors, meaningful comparison between different manufacturer's scanners is difficult, as are comparisons between different acquisition geometries (e.g. with and without interplane septa present). A method has been developed in our laboratory that provides measurements of absolute sensitivity in air for a scanner independent of attenuation and scatter within the source. The method involves measurements of a thin-line source of fluorine 18 contained within an aluminium housing to which successive aluminium sleeves are added. The extrapolation of these measurements allows an effective counts.s-1.MBq-1 measurement to be made for zero thickness of aluminium. Measurements have yielded absolute sensitivities of 3926 +/- 61 counts.s-1.MBq-1 (0.39% efficiency), 5079 +/- 26 counts.s-1.MBq-1 (0.51%), and 32312 +/- 544 counts.s-1.MBq-1 (3.2%) for a whole-body PET scanner with interplane septa and for a NeuroPET operating with and without interplane septa, respectively.

Calibration↗
PubMed1991

Mechanistic studies of the phototoxic potential of PD 117596, a quinolone antibacterial compound.

PD 117596 is a novel quinolone compound that is being investigated for use as an antibacterial agent. Early investigations demonstrated a significant phototoxic liability associated with this compound. These studies were undertaken to investigate the mechanism of phototoxicity using an in vitro model. In the UVA region, PD 117596 was found to be a more efficient producer of singlet oxygen than rose bengal, ciprofloxacin, nalidixic acid, or PD 118879, another quinolone under investigation. The quantum yield of photoreaction for PD 117596 was relatively low (phi = 0.021); however, it was approximately 10-fold higher than other tested quinolones. In vitro studies using a mouse erythrocyte model were used to further investigate the mechanism of phototoxicity. PD 117596-induced photohemolysis was found to be oxygen dependent with a relatively rapid onset that progressed even after removal of light. Preirradiation of the compound prevented subsequent hemolytic or photohemolytic action. BHA, BHT, alpha-tocopherol, and the iron chelator DTPA were all found to be effective at ameliorating the photohemolytic response. The photohemolytic response was markedly enhanced when D2O was substituted for H2O in the incubation medium, indicating a singlet oxygen-mediated mechanism of action. A rise in thiobarbituric acid products was noted within 1 hr of irradiation and was maximal at the time of onset of overt photohemolysis. These data suggest that singlet oxygen production by irradiated PD 117596 is responsible for secondary changes in mouse red blood cells including lipid peroxidation and ultimately results in cellular lysis.

4-Quinolones↗
PubMed1991

Dynamic monitoring of [11C]diprenorphine in rat brain using a prototype positron imaging device.

The present work tests the feasibility of using the most recently developed positron emission tomograph detector technology to image positron-emitting radioligands in small experimental animals. A prototype imaging device, using two opposing multicrystal, high-resolution (approximately 4 mm) block detectors of bismuth germanate to produce a 2-dimensional image in the centre of the field of view, is described. To evaluate the probe's potential as a non-invasive experimental tool, the dynamic regional distribution of the established opiate receptor ligand, [11C]diprenorphine was determined in rat brain following intravenous injection. The distribution of counts in the images was consistent with the localisation of diprenorphine binding sites and the specificity of the signal obtained was confirmed by administration of non-radioactive diprenorphine and naloxone. Although the signal-to-noise ratio was reduced compared with data obtained by post mortem dissection, the dynamic data acquisition capabilities of the system demonstrate the feasibility of monitoring the kinetics of ligand binding in individual animals and encourages further design of a small-diameter detector system with tomographic capabilities.

Animals↗
PubMed1991

Species differences in response to photohemolytic agents.

Species differences in red blood cell susceptibility to the photohemolytic agents chlorpromazine, menadione and tetracycline were examined in mouse, rat, dog, and human blood. Menadione and tetracycline (25 microM) hemolyzed mouse but not dog, rat, or human red blood cells (RBC) when irradiated with UV light but not in the dark. Chlorpromazine (25 microM) produced a photohemolytic response in all four species with mouse and rat RBC lysing fastest followed by human then dog cells. Investigations into the nature of these species differences suggested that the size of mouse RBC may contribute to its high sensitivity to photohemolytic agents. An investigation of the effect of UV light on key antioxidant enzymes revealed species differences in enzyme inactivation. These data suggest that mouse RBC may be particularly vulnerable to phototoxic agents, especially those compounds which produce active oxygen species and, therefore, may prove more useful than human RBC as a model for predicting phototoxic potential of some chemical entities.

Animals↗
PubMed1991

Normalisation and reconstruction of PET data acquired by a multi-ring camera with septa retracted.

Emission scan data acquired by a multi-ring PET camera operated with septa retracted must be corrected for (1) geometrical and detector sensitivity variations between the different lines of response (normalisation), (2) photon attenuation, and (3) mispositioned events due to photon scattering. These corrections must be applied to the full 3-D set of lines of response before reconstruction. The standard normalisation and attenuation correction procedures for 2-D scans increase the statistical noise in the emission scan, a problem which becomes even more serious in 3-D because of the large number of LORs involved (approximately 8 million). This paper will describe a fully 3-D reconstruction algorithm for multi-angle PET data incorporating a practical normalisation and attenuation correction procedure which minimises the increase in emission scan statistical noise. The correction factors are derived from 2-D, septa extended scans. The algorithm is currently used to reconstruct 3-D emission data from an ECAT 953B, a sixteen-ring PET camera with retractable septa.

Algorithms↗
PubMed1989

A standard protocol for the exchange of nuclear medicine image files.

In order to meet an increasing demand for a standard file format which would facilitate the exchange of image files from one computer to another, the protocol initiated by Report #10 of the American Association of Physicists in Medicine has been adopted. This protocol uses the concept of an ASCII file in which key-value pairs are used to describe the various parameters of the image file. Keys specific to nuclear medicine image files have been established and are published here. In addition, the latest version of the keys has been placed on a list server which is accessible by electronic mail. This will facilitate the development of conversion programs which will also be placed on the same list server as they become available.

Computer Systems↗
PubMed1989

Neutrophilic eccrine hidradenitis: a case report and review of the literature.

Neutrophilic eccrine hidradenitis (NEH) is a recently recognized dermatosis occurring in patients receiving chemotherapy for a variety of malignancies. We report the second pediatric case. An 11-year-old boy with non-Hodgkin's lymphoma developed widespread erythematous papulopustules beginning two days after receiving high-dose cytarabine (Ara-C) in preparation for a bone marrow transplant. The lesions spontaneously regressed in two weeks. Histologic examination revealed a neutrophilic infiltrate around and within the eccrine ducts and secretory coils. Bacterial, fungal, and viral cultures were negative. These findings are characteristic of NEH. The condition should be differentiated from infectious dermatoses that may require treatment.

Child↗
PubMed1989

Comparisons of planar and tomographic gamma scintigraphy to measure the penetration index of inhaled aerosols.

The quantitative measurement of regional aerosol deposition in human lungs using two-dimensional (2D) gamma scintigraphy has proven to be useful in therapeutic and diagnostic aerosol studies. The penetration index (PI) has been defined as the ratio of activity in a peripheral lung zone to a central lung zone, but the ability to discriminate between aerosol deposition in the large airways and lung parenchyma is reduced by the fact that the latter overlies the former in the central zone. To overcome this, we used a three-dimensional (3D) technique. Seven healthy subjects inhaled isotonic saline aerosols containing 99mTc-DTPA on two occasions. The droplets had a mass median aerodynamic diameter (MMAD) of either 2.6 or 5.5 microns (with geometric standard deviations [sigma g] of 1.4 and 1.7, respectively). Transmission tomography was performed on each subject to delineate lung boundaries in 2D and 3D. After inhalation, anterior (A) and posterior (P) images were collected and a tomographic study performed. Mid-lung slices were taken from coronal (CC) and transverse (TC) sections. PI was calculated on the 2D images (AP and P) and the 3D slices (CC and TC) using exactly defined regions. The PI values were smaller for the large droplet aerosol (5.5 microns) in all subjects and methods. The relative differences in PI between large and small (2.6 microns) droplet studies (d values) were greater and less variable for the 3D methods (TC, 56.5 +/- 11.4% and CC, 52.4 +/- 12.3%) compared to the 2D methods (P, 25.4 +/- 17.1% and AP, 38.3 +/- 15%; p less than 0.005). We found the 3D methods to be more sensitive for discriminating between aerosol deposition in large and small airways than were the conventional 2D methods.

Adult↗
PubMed1989

Dynamic geometric mean studies using a single headed rotating gamma camera.

A technique for acquiring dynamic geometric mean studies utilizing a single-headed rotating gamma camera has been developed. The camera head is repeatedly rotated between opposed views under computer control. A single data set results, from which a dynamic sequence of geometric mean images can be produced. Software has been developed to accomplish data acquisition and the reformatting required. The accuracy of the geometric mean data formed using this technique has been studied experimentally, and compared with results obtained from anterior and posterior sequences. In a simple clearance experiment of a 1-I volume with a known clearance of 20 ml.min-1, the geometric mean data resulted in estimates of volume remaining in the container with a mean error or +2.0 ml (s.d. = 5.7 ml, range -4.5 +/- 15.3 ml), while the anterior and posterior images yielded volume estimates with mean errors of -10.1 ml (s.d. = 16.6 ml, range -47.4 +/- 10.5 ml) and +35.5 ml (s.d. = 22.6 ml, range -3.2 +/- 51.6, ml), respectively. The technique is easy to implement and does not require modification of existing hardware. An application of the technique to a clinical study of gastric emptying is also included.

Gamma Cameras↗
PubMed1988

SPECT evaluation of arterial perfusion in regional chemotherapy.

Simultaneous emission and transmission tomography was performed after the injection of [99mTc]MAA in 30 patients undergoing intra-arterial chemotherapy to nonhepatic sites to determine the accuracy of catheter placement. The transmission and emission data were reconstructed in transverse, and optionally, coronal and sagittal planes. The correlation of the emission scan with the reconstructed transmission data allowed accurate anatomical localization of the infusate distribution. In seven patients, catheter placement resulted in perfusion to nontumor sites, and hence required repositioning. MAA accumulation was seen in the lungs of all patients, regardless of tumor site, indicating arterio-venous shunting of the MAA. The degree of uptake in the lungs was quantified from planar anterior/posterior thorax images in terms of injected dose in ten patients, with values of 5-50% of injected dose present in the lungs. The technique provides a noninvasive means of accurately determining regional perfusion of chemotherapeutic agents delivered intra-arterially.

Adult↗
PubMed1987

Artefact reduction in dual-radionuclide subtraction studies.

A method is proposed which significantly reduces the artefacts commonly experienced in dual radionuclide subtraction studies. Images of two radionuclides recorded simultaneously differ in resolution, sensitivity and attenuation. Also, one image will include scatter from the second higher-energy radionuclide. As a result severe artefacts are likely to occur when the two images are subtracted. In order to minimise the depth dependence of resolution, attenuation and scatter, the geometric mean of conjugate views was considered. From experimental work with activity placed in a depth of water it was demonstrated that the number and spatial distribution of scattered photons recorded in any energy window could be accurately predicted from the geometric mean image recorded in the photopeak. This prediction was accurate, independent of the depth of the source in water for a range of phantom dimensions. Differences in the instrument sensitivity and resolution at different energies can also be readily compensated for by using geometric mean images, as can differences due to the variation in attenuation. In practice three factors can be experimentally determined for any pair of radionuclides: a scatter ratio, a scatter function and a resolution compensation function. These data are then used to improve the dual-radionuclide subtraction analysis. The ability of the technique to significantly reduce subtraction artefacts has been demonstrated in phantom studies.

Humans↗
PubMed1987

Improved SPECT using simultaneous emission and transmission tomography.

A method is proposed to simultaneously record single photon emission and transmission tomographic (SPECT) studies to produce a map of attenuation coefficients (mu) for the body. A dual radionuclide SPECT acquisition is performed with a transmission source attached to a rotating gamma camera of lower energy than the emission radionuclide. Scatter from the emission source into the transmission window is removed by subtracting the predicted scatter distribution. The transmission image is then reconstructed to yield the map of attenuation coefficients for anatomic display or attenuation correction purposes. Experimental work has shown that the method can accurately derive mu values to +/- 2.5% in both phantom and patient studies, without increasing acquisition time. Preliminary attenuation correction experiments have demonstrated an accuracy of better than 5% for estimated activity.

Gadolinium↗