Search PubMed⌕ Search

Biomedical subjects

D L Bailey

Publications and source records attributed to D L Bailey.

At least 37 records · Page 2Linked to original sources
PubMed1998

Experience with fully 3D PET and implications for future high-resolution 3D tomographs.

The aim of this paper is to report on experience with 3D positron emission tomography (PET) in our institute where we have three 3D scanners, of which two operate exclusively in 3D mode (ECAT ART, EXACT 3D). Fully 3D PET requires attention to a number of factors which are not as problematic in 2D PET. Firstly, 3D tomographs designed for whole-body acquisition suffer from a large single-photon field of view, extending well beyond the coincidence field of view. Single photons from outside the coincidence field of view increase the dead time and random coincidence rates, and contribute scattered events. For brain studies, we have extended the lead side shielding at the ends of the tomograph to mitigate against these effects, and this has dramatically improved the count rate performance. This approach is not as effective for whole-body scanning. In addition, operating in 3D without septa necessitates new approaches to transmission scanning, as measurements using positron emitters such as 68Ge/68Ga have the unfavourable characteristics of high dead time and high scatter. Both of our fully 3D scanners use 137Cs for single-photon transmission measurements, although the data are treated differently. On the ECAT ART, a combination of physical and electronic collimation effectively reduces transmission scatter to acceptable levels. On the EXACT 3D physical collimation is not as readily implemented and therefore segmentation and reassignment of the histogrammed attenuation (mu) values is employed to produce unbiased attenuation correction factors in 3D. Many of the lessons learnt with these BGO (bismuth germanate) based tomographs will be applicable to the next generation of systems using faster detectors such as lutetium oxyorthosilicate (LSO).

Brain↗
PubMed1998

The effect of activity outside the direct field of view in a 3D-only whole-body positron tomograph.

The ECAT EXACT3D (CTI/Siemens 966) 3D-only PET tomograph has unprecedented sensitivity due to the large BGO (bismuth germanate) detector volume. However, the consequences of a large (23.4 cm) axial field-of-view (FOV) and the need for a patient port diameter to accommodate body scanning make the device more sensitive to photons arising from activity outside the direct (coincidence) FOV. This leads to relatively higher deadtime and an increased registration of random and scatter (true) coincidences. The purpose of this study is to determine the influence of activity outside the FOV on (i) noise-equivalent counts (NEC) and (ii) the performance of a 'model-based' scatter correction algorithm, and to investigate the effect of side shielding additional to that supplied with the tomograph. Annular shielding designed for brain scanning increased the NEC for blood flow (H[2]15O) measurement (integrated over 120 s) by up to 25%. For 11C tracer studies, the increase is less than 5% over 120 min. Purpose-built additional body shielding, made to conform to the shape of a volunteer, reduced the randoms count rate in a heart blood flow measurement (H[2]15O) by about 30%. After scatter correction the discrepancy between ROI count ratios for compartments within the 20 cm diameter 'Utah' phantom differed by less than 5% from true (sampled) activity concentration ratios. This was so with or without activity outside the FOV and with or without additional side shielding. Count rate performance is thus improved by extra shielding but more improvement is seen in head than in body scanning. Measurement of heart blood flow using bolus injections of H(2)15O would benefit from the use of detectors with lower deadtime and superior timing resolution such as LSO (lutetium oxyorthosilicate).

Algorithms↗
PubMed1998

Measuring the rate of progression and estimating the preclinical period of Parkinson's disease with [18F]dopa PET.

OBJECTIVES: To measure the rate of progression in striatal [18F]dopa metabolism in a large group (n=32) of patients with Parkinson's disease, to estimate the average duration of preclinical period, and to examine the influence of the PET method on the assessment of rate of progression and preclinical period. METHODS: Thirty two patients with Parkinson's disease (mean age 58 (SD 13) years, mean duration 39 (SD 33) months) were assessed with [18F]dopa PET and UPDRS scoring on two occasions a mean of 18 (SD 6) months apart. PET data were sampled with separate caudate and putamen and total striatal regions of interest, and both graphical (Ki) and ratio methods of analysis. RESULTS: The mean annual rate of deterioration in [18F]dopa uptake varied according to structure and method of analysis, with putamen Ki showing the most rapid mean rate of progression (4.7% of normal mean per year). The group showed a significant deterioration (p<0.0004, paired two tailed t test) in UPDRS and in the putamen (p=0.008) and total striatal (p=0.012) [18F]dopa uptake measured using a graphical analysis, but no significant change in caudate or putamen uptake measured by a ratio approach. A study of sensitivity confirmed that putamen Ki was the most sensitive measure of disease progression, caudate ratio the least. Symptom onset in Parkinson's disease was estimated at a mean putamen [18F]dopa uptake (Ki) of 75% of normal and a mean caudate [18F]dopa uptake (Ki) of 91% of normal. CONCLUSIONS: Estimation of mean rate of progression varies according to the sensitivity of a functional imaging method to clinical severity. Sensitivity and reproducibility of method must be considered when designing studies of disease progression and neuroprotection. The mean preclinical period in Parkinson's disease is unlikely to be longer than seven years.

Aged↗
PubMed1997

A method for calibrating three-dimensional positron emission tomography without scatter correction.

Calibration for three-dimensional positron emission tomography (3D PET) using a uniform cylinder and cross-calibration with aliquots requires correction for scatter and attenuation. Thus the accuracy of the calibration is dependent on the scatter correction method, and on the applicability of the scatter correction for different regions of the body. A method has been developed which provides a calibration which does not require correction for scatter or attenuation, making it generally applicable and independent of the scatter correction. The method has been previously described for measurement of the absolute sensitivity of tomographic devices. This approach has been extended to give a calibration of the PET camera "in air" in units of kBq/pixel. The reconstructed images are multiplied by this factor to give accurate activity concentrations, after attenuation and scatter correction. The method has been used with a fully 3D filtered backprojection (reprojection) algorithm and iterative convolution-subtraction scatter correction on data from an ECAT 953B. Using this method 3D PET images have been calibrated to within +/-5% accuracy, but this is highly dependent on the accuracy of the scatter correction. The method described here is practical and provides a means of calibrating a 3D PET system without the need for correction for scatter or attenuation of the calibration data.

Algorithms↗
PubMed1997

ECAT ART - a continuously rotating PET camera: performance characteristics, initial clinical studies, and installation considerations in a nuclear medicine department.

Advances in fully three-dimensional (3D) image reconstruction techniques have permitted the development of a commercial, rotating, partial ring, fully 3D positron emission tomographic (PET) scanner, the ECAT ART. The system has less than one-half the number of bismuth germanate detectors compared with a full ring scanner with the equivalent field of view, resulting in reduced capital cost. The performance characteristics, implications for installation in a nuclear medicine department, and clinical utility of the scanner are presented in this report. The sensitivity (20 cm diameterx20 cm long cylindrical phantom, no scatter correction) is 11400 cps.kBq-1.ml-1. This compares with 5800 and 40500 cps.kBq-1.ml-1 in 2D and 3D respectively for the equivalent full ring scanner (ECAT EXACT). With an energy window of 350-650 keV the maximum noise equivalent count (NEC) rate was 27 kcps at a radioactivity concentration of approximately 15 kBq.ml-1 in the cylinder. Spatial resolution is approximately 6 mm full width at half maximum on axis degrading to just under 8 mm at a distance of 20 cm off axis. Installation and use within the nuclear medicine department does not appreciably increase background levels of radiation on gamma cameras in adjacent rooms and the dose rate to an operator in the same room is 2 microSv. h-1 for a typical fluorine-18 fluorodeoxyglucose (18F-FDG) study with an initial injected activity of 370 MBq. The scanner has been used for clinical imaging with18F-FDG for neurological and oncological applications. Its novel use for imaging iron-52 transferrin for localising erythropoietic activity demonstrates its sensitivity and resolution advantages over a conventional dual-headed gamma camera. The ECAT ART provides a viable alternative to conventional full ring PET scanners without compromising the performance required for clinical PET imaging.

Equipment Design↗
PubMed1997

Effect of increasing doses of hypertonic saline on mucociliary clearance in patients with cystic fibrosis.

BACKGROUND: Patients with cystic fibrosis are known to have decreased mucociliary clearance. It has previously been shown that inhalation of a 7.0% solution of hypertonic saline significantly improved mucociliary clearance in a group of adult patients with cystic fibrosis. The aim of this study was to measure the response to increasing concentrations of inhaled hypertonic saline. METHODS: Ten patients (seven men) of mean (SE) age 22 (4) years and mean forced expiratory volume in one second (FEV1) 52.0 (6.7)% predicted completed the study. Mucociliary clearance was measured using a radioaerosol technique for 90 minutes after the interventions which comprised 0.9% NaCl + voluntary cough (control), 3.0% NaCl, 7.0% NaCl, and 12% NaCl. RESULTS: There was a significant increase in the amount of activity cleared from the right lung with all concentrations of hypertonic saline (HS) compared with control. The amount cleared at 90 minutes on the control day was 12.7% (95% confidence interval (CI) 9.8 to 17.2) compared with 19.7% (95% CI 13.6 to 29.5) for 3% HS, 23.8% (95% CI 15.9 to 36.7) for 7% HS and 26.0% (95% CI 19.8 to 35.9) for 12% HS. The improvement in mucociliary clearance was not solely due to coughing as the number of coughs recorded on the control day exceeded that recorded on any other day. The hypertonic saline did not induce a clinically significant change in FEV1. CONCLUSIONS: Within the range of concentrations examined in this study, the effect of hypertonic saline appears to be dose dependent. Inhalation of hypertonic saline remains a potentially useful treatment for patients with cystic fibrosis.

Administration, Inhalation↗
PubMed1996

The effect of a selective estrogen receptor modulator on the progression of spontaneous autoimmune disease in MRL lpr/lpr mice.

The MRL lpr/lpr mouse strain is an animal model for the autoimmune disorder systemic lupus erythematosus (SLE). Pathologic changes in the mice include a severe proliferative glomerulonephritis, lymph node and spleen enlargement, increase in autoantibody titers, and shortened life spans. In the present investigation, female MRL lpr/lpr mice have been dosed po daily for 7 months with the selective estrogen receptor modulator (SERM) LY139478 (4 mg/kg) or 17alpha-ethinylestradiol (EE2, 1 mg/kg) and compared to vehicle control animals. The LY139478 group had an increase in survival (73% survival at 7 months, P = 0.02) but the EE2-treated animals did not (53% survival at 7 months, P = 0.4) when compared to the control group (32% survival at 7 months). Although there were no reductions in autoantibody levels as determined by anti-DNA antibody ELISA, histological analysis of kidney tissue indicated that both LY139478 and EE2 mitigated the progression of glomerular nephritis which was evident in the controls. In contrast, there were no significant differences in lymph node size although the LY139478 and EE2 groups retained a well-defined sinusoidal region. Finally, flow cytometric analysis documented that thymuses from animals treated for 7 months with LY139478 but not with EE2 contained predominantly CD4+/CD+ T cells consistent with a normal thymic phenotype observed in non-MRL lpr/lpr mouse strains. These studies demonstrate that SERMs may be potentially useful for the treatment of autoimmune disorders.

Animals↗
PubMed1996

Simultaneous emission and transmission measurements as an adjunct to dynamic planar gamma camera studies.

Anatomical imaging provides useful information which complements functional imaging performed using a gamma camera. We have previously used transmission measurements in single-photon emission tomography acquired simultaneously with the emission scan using either a plane flood source or a moving line source for attenuation and scatter correction. This approach is equally applicable in planar imaging and provides useful information to assist in detecting patient motion and in defining regions of interest in dynamic studies. We have adapted a moving transmission line source to acquire dynamic geometric mean measurements in the study of the mucociliary clearance of inhaled technetium-99m labelled colloids with a single-headed rotating gamma camera. The line source makes a return pass for each emission acquisition frame (alternating anterior/posterior views), each pass being initiated by a signal from the gamma camera. The result is a dynamic sequence of emission and transmission measurements obtained from a single acquisition. In this application transmission measurements are used to define the lung outline for clearance determination and to check for subject movement throughout the duration of the study.

Gamma Cameras↗
PubMed1996

Non-invasive measurement of left ventricular volumes and function by gated positron emission tomography.

To date cardiac positron emission tomography (PET) studies have focussed on the measurement of myocardial blood flow, metabolism and receptors while left ventricular (LV) function and dimensions have been derived from other modalities. The main drawback of this approach is the difficulty of data co-registration, which limits clinical interpretation. The aim of this study was to evaluate whether it is possible to measure absolute cardiac volumes, and consequently LV function parameters such as ejection fraction, and wall motion with gated PET. Nineteen patients underwent a PET scan and planar radionuclide ventriculography (MUGA) within 9+/-9 days. A 9-min scan (16 gates/cardiac cycle) was acquired after inhalation of 3 MBq/ml of oxygen-15 labelled carbon monoxide at the rate of 500 ml/min over 4 min using a multislice PET camera. Noise reduction was performed on the gated image to enhance the definition of the ventricles before reslicing to the short-axis view. A threshold value was used to detect the edge of the LV at each gate. LV volumes at each gate were estimated by summing the volume of voxels within the LV boundary. PET measurements of LV volumes were as follows: LV end-diastolic volume ranged from 72 to 233 ml and LV end-systolic volume ranged from 24 to 203 ml. Phantom experiments supported the validity of this approach for estimating volumes. LV ejection fraction measured with MUGA was 38.4%+/-16.3% (range 15%-71%) and that measured with PET was 39.6%+/-17.7% (range 9%-72%) (P=NS). The LV ejection fraction measurements were highly correlated (r2=0.824). These results indicate that: (1) absolute end-diastolic and end-systolic volumes can be quantified using gated PET and (2) LV ejection fraction can be accurately measured by gated PET simultaneously with the other physiological PET parameters.

Coronary Disease↗
PubMed1996

Effect of hypertonic saline, amiloride, and cough on mucociliary clearance in patients with cystic fibrosis.

In patients with cystic fibrosis (CF), dehydration of airway secretions leads to a decrease in mucociliary clearance (MCC). We examined the acute effect of MCC of a single administration by aerosolization of hypertonic saline (7%) (HS), amiloride (0.3% in 0.12% NaCl) (AML) and a combination of AML and HS (AML + HS) in 12 patients with CF using a radioaerosol technique. Isotonic saline [0.9%] (IS) was used as a control solution. As both the AML and HS solutions induced cough in some patients, the last nine patients studied also underwent a cough clearance day. This was to eliminate the possible confounding effect of cough on MCC measurement. Patients ranged from 18 to 28 yr (mean +/- SD, 22 +/- 3) with an FEV1 of 27 to 112% predicted (61 +/- 30%). Following deposition of the radioaerosol, baseline clearance was assessed for 30 min. This was followed by a 30-min intervention period. Assessment of post-intervention clearance for a further 30 min was then performed. Comparison of the amount of radioaerosol cleared from the right lung was made at 60 min (%C60) and 90 min (%C90) using repeated measures ANOVA. The percent cleared at 60 and 90 min was significantly increased with HS (%C60 = 26.5%, %C90 = 29.4%) and the combination of AML + HS (%C60 = 23.1%, %C90 = 27.4%) compared with both IS (%C60 = 14.7%, %C90 = 17.5%) and COUGH (%C60 = 18.0%, %C90 = 19.5%), p < 0.01. Inhalation of hypertonic saline is a potentially useful treatment in patients with cystic fibrosis.

Adolescent↗
PubMed1995

Simultaneous emission and transmission measurements for attenuation correction in whole-body PET.

UNLABELLED: We describe a methodology for measuring and correcting for attenuation in whole-body PET using simultaneous emission and transmission (SET) measurements. METHODS: The main components of the methodology are: (a) sinogram windowing of low activity (< or = 50 MBq) rotating 68Ge/Ga rod sources, (b) segmented attenuation correction (SAC) and (c) maximum likelihood reconstruction using the ordered subsets EM (OS-EM) algorithm. The methods were implemented on a whole-body positron emission tomograph. Quantitative accuracy and the signal-to-noise ratio (SNR) were measured for a thorax-tumor phantom as functions of acquisition time (range: 2-20 min per position). RESULTS: When a typical rod source activity (200 MBq 68Ge/Ga) was used, emission SNR was 60% lower in simultaneous than in separate measurements. The difference was only 14% when the rods contained 45 MBq 68Ge/Ga. The SNR was further improved by SAC in conjunction with OS-EM reconstruction and the relative gain increased with increasing acquisition time. Quantitative estimates of tumor, liver and lung radioactivity agreed with values obtained from a separate high count measurement to within 8%, independent of acquisition time. CONCLUSION: Attenuation correction of whole-body PET images is feasible using SET measurements. There is good quantitative agreement with conventional methods and increased noise is offset by the use of SAC and OS-EM reconstruction.

Adult↗
PubMed1994

Performance comparison of a state-of-the-art neuro-SPET scanner and a dedicated neuro-PET scanner.

The physical performances of two current state-of-the-art scanners dedicated to functional imaging of the brain, one a single-photon emission tomography (SPET) scanner and the other a positron emission tomography (PET) scanner, have been compared under identical conditions. The aim of the study was to compare the capabilities of the devices under conditions resembling the routine clinical environment, as well as to consider other issues such as radiation burden for some common investigations. Both systems have slightly less than 11-cm axial fields of view. The PET system can be operated in a septa-less (3D) mode as well as conventionally with septa (2D). The spatial resolution of both devices was less than 8 mm in all dimensions in scattering media. On average, the PET scanner's resolution was approximately 10%-15% better than the SPET system. Energy resolution on the SPET system was superior due the scintillator used [NaI(Tl)]. Sensitivity in air with a line source on the PET system was found to be approximately 150 times greater in 3D and approximately 25 times greater in 2D than with the SPET system. A normal subject was studied on each system in an attempt to obtain the highest quality data possible for a subjective comparison. It is clear that, while PET retains the advantages of more desirable radiopharmaceuticals and higher sensitivity, the quality obtainable from SPET devices has improved markedly. SPET may prove as useful for many clinical investigations.

Brain↗
PubMed1994

Accelerated EM reconstruction in total-body PET: potential for improving tumour detectability.

Total-body positron emission tomography (PET) is a useful diagnostic tool for evaluating malignant disease. However, tumour detection is limited by image artefacts due to the lack of attenuation correction and noise. Attenuation correction may be possible using transmission data acquired after or simultaneously with emission data. Despite the elimination of attenuation artefacts, however, tumour detection is still hampered by noise, which is amplified during image reconstruction by filtered backprojection (FBP). We have investigated, as an alternative to FBP, an accelerated expectation maximization (EM) algorithm for its potential to improve tumour detectability in total-body PET. Signal to noise ratio (SNR), calculated for a tumour with respect to the surrounding background, is used as a figure of merit. A software tumour phantom, with conditions typical of those encountered in a total-body PET study using simultaneous acquisition, is used to optimize and compare various reconstruction approaches. Accelerated EM reconstruction followed by two-dimensional filtering is shown to yield significantly higher SNR than FBP for a range of tumour sizes, concentrations and counting statistics (deltaSNR = 6.3 +/- 3.9, p < 0.001). The methods developed are illustrated by examples derived from physical phantom and patient data.

Algorithms↗
PubMed1994

A convolution-subtraction scatter correction method for 3D PET.

3D acquisition and reconstruction in positron emission tomography (PET) produce data with improved signal-to-noise ratios compared with conventional 2D slice-oriented methods. However, the sensitivity increase is accompanied by an increase in the number of scattered photons and random coincidences detected. This paper presents a scatter correction technique for 3D PET data where an estimate of the scattered photon distribution is subtracted from the data before reconstruction. The scatter distribution is estimated by iteratively convolving the photopeak projections with a mono-exponential kernel. The method accounts for the 3D acquisition geometry and nature of scatter by performing the scatter estimation on 2D projections. The assumptions of the method have been investigated by measuring the variation in the scatter fraction and the scatter function at different positions in a cylinder. Both parameters were found to vary by up to 50% from the centre to the edge of a large water-filled cylinder. Despite this, in a uniform cylinder containing water with different concentrations of radioactivity, scatter was reduced from 25% in a non-radioactive region to less than 5% using the convolution-subtraction method. In addition, the relative concentration of a cylinder containing an increased concentration, which was underestimated by almost 50% without scatter correction, was within 5% of the true concentration after correction.

Algorithms↗
PubMed1994

Mucociliary clearance in patients with cystic fibrosis and in normal subjects.

The aim of this study was to examine baseline mucociliary clearance (MCC) in patients with cystic fibrosis (n = 30; mean +/- SEM age, 23 +/- 1 yr; FEV1, 68 +/- 5% pred; range, 14 to 126%) and a group of normal subjects (n = 12; mean age, 27 +/- 1 yr) after an aerosol deposition of 99mTc-sulphur colloid (mass median diameter, 4.8 microns; geometric standard deviation, 1.6). Dynamic geometric mean images were formed from gamma camera data, and the percent clearance of activity after 60 min (%C60) was calculated for the whole right lung. Initial deposition of the aerosol was determined in terms of the penetration index, the ratio of peripheral to central activity. For normal subjects, an increase in mean inspiratory flow rate (MIFR) (49 +/- 5 versus 21 +/- 3 L/min, p < 0.05) resulted in an increase in whole right lung MCC (%C60, 31 +/- 4 versus 18 +/- 2%; p < 0.05). When aerosol delivery was controlled (MIFR, 34 +/- 5 versus 36 +/- 5 L/min), there was excellent reproducibility between studies (whole lung %C60, 34 +/- 8 versus 31 +/- 7; NS). The measurement of MCC was highly reproducible in six patients studied on four occasions with a mean coefficient of variation of 3.3 +/- 1%. A breathing pattern to accentuate central deposition was utilized in the patient studies (MIFR, 49 +/- 4 L/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

A transmission-dependent method for scatter correction in SPECT.

UNLABELLED: A method of scatter compensation has been developed that incorporates planar transmission measurements in the estimation of photopeak scatter in SPECT. METHODS: The scatter distribution is first estimated by convolving the planar projections with a monoexponential scatter function. The number of scattered events that subsequently reach the detector as a proportion of total events (i.e., scatter fraction) is then determined for each point in the projections based on narrow-beam transmission values, obtained using an external source. The assumptions of the method were tested using 99mTc and 201Tl point and line sources. The quantitative and qualitative impact of transmission-dependent scatter correction was assessed in realistic phantom experiments simulating blood-pool, lung and myocardial perfusion studies. RESULTS: The method accurately predicts the scatter distribution from 99mTc and 201Tl line sources in a phantom with variable density. Reconstructed counts are artificially enhanced in regions of high tissue density when scattered events are not removed from the projections prior to attenuation correction. Using convolution-subtraction with a constant scatter fraction (k = 0.4), scatter is underestimated in the heart and overestimated in the lungs, whereas transmission-dependent scatter correction enables activity to be quantified with > or = 95% accuracy in heart and lung regions. CONCLUSION: We conclude that incorporating transmission data enables accurate scatter compensation in objects with nonuniform density.

Female↗
PubMed1993

Cloning, characterization, and expression of the beta subunit of pig heart succinyl-CoA synthetase.

The form of succinyl-CoA synthetase found in mammalian mitochondria is known to be an alpha beta dimer. Both GTP- and ATP-specific isozymes are present in various tissues. We have isolated essentially identical complementary DNA clones encoding the beta subunit of pig heart succinyl-CoA synthetase from both newborn and adult tissues. These cDNAs include a 1.4-kb sequence encoding the cytoplasmic precursor to the beta subunit comprised of 417 amino acid residues including a 22-residue mitochondrial targeting sequence. The cDNA encoding the 395-amino acid, 42,502-Da mature protein was confirmed to be the succinyl-CoA synthetase beta subunit by agreement with the N-terminal protein sequence and by high homology to prokaryotic forms of the beta subunit that were previously cloned (about 45% identical to beta from Escherichia coli). In contrast to a previous report (Nishimura, J.S., Ybarra, J., Mitchell, T., & Horowitz, P.M., 1988, Biochem. J. 250, 429-434), we found no tryptophan residue to be encoded in the sequence for the mature beta subunit, and this finding is corroborated by the fact that highly purified pig heart succinyl-CoA synthetase shows no tryptophan fluorescence or tryptophan content in amino acid compositional analysis. The cDNA clones encoding the mature pig heart beta subunit and its counterpart alpha subunit were coexpressed in a deletion mutant strain of E. coli. Recovery of succinyl-CoA synthetase activity demonstrated that this combination of subunits forms a productive enzymatic complex having GTP specificity.

Aging↗