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Biomedical subjects

T Spinks

Publications and source records attributed to T Spinks.

18 recordsLinked to original sources
PubMed2002

Diagnostic features of Alzheimer's disease extracted from PET sinograms.

Texture analysis of positron emission tomography (PET) images of the brain is a very difficult task, due to the poor signal to noise ratio. As a consequence, very few techniques can be implemented successfully. We use a new global analysis technique known as the Trace transform triple features. This technique can be applied directly to the raw sinograms to distinguish patients with Alzheimer's disease (AD) from normal volunteers. FDG-PET images of 18 AD and 10 normal controls obtained from the same CTI ECAT-953 scanner were used in this study. The Trace transform triple feature technique was used to extract features that were invariant to scaling, translation and rotation, referred to as invariant features, as well as features that were sensitive to rotation but invariant to scaling and translation, referred to as sensitive features in this study. The features were used to classify the groups using discriminant function analysis. Cross-validation tests using stepwise discriminant function analysis showed that combining both sensitive and invariant features produced the best results, when compared with the clinical diagnosis. Selecting the five best features produces an overall accuracy of 93% with sensitivity of 94% and specificity of 90%. This is comparable with the classification accuracy achieved by Kippenhan et al (1992), using regional metabolic activity.

Adult↗
PubMed2000

Enhanced 3D PET OSEM reconstruction using inter-update Metz filtering.

We present an enhancement of the OSEM (ordered set expectation maximization) algorithm for 3D PET reconstruction, which we call the inter-update Metz filtered OSEM (IMF-OSEM). The IMF-OSEM algorithm incorporates filtering action into the image updating process in order to improve the quality of the reconstruction. With this technique, the multiplicative correction image--ordinarily used to update image estimates in plain OSEM--is applied to a Metz-filtered version of the image estimate at certain intervals. In addition, we present a software implementation that employs several high-speed features to accelerate reconstruction. These features include, firstly, forward and back projection functions which make full use of symmetry as well as a fast incremental computation technique. Secondly, the software has the capability of running in parallel mode on several processors. The parallelization approach employed yields a significant speed-up, which is nearly independent of the amount of data. Together, these features lead to reasonable reconstruction times even when using large image arrays and non-axially compressed projection data. The performance of IMF-OSEM was tested on phantom data acquired on the GE Advance scanner. Our results demonstrate that an appropriate choice of Metz filter parameters can improve the contrast-noise balance of certain regions of interest relative to both plain and post-filtered OSEM, and to the GE commercial reprojection algorithm software.

Algorithms↗
PubMed1999

The effects of 10 years of recombinant human growth hormone (GH) in adult GH-deficient patients.

The long term effects of GH replacement in adult GH-deficient (GHD) patients have not yet been clarified. We studied 21 GHD adults who originally took part in a randomized, double blind, placebo-controlled trial of GH treatment in 1987. After completion of that trial, 10 patients received continuous GH replacement for the subsequent 10 yr, whereas 11 did not. A group of 11 age- and sex-matched normal controls were also studied in 1987 and 1997. Lean body mass, as assessed by total body potassium measurement and computed tomography scanning of the dominant thigh, increased in the GH-treated group (P < 0.01 for both) only (P < 0.05 between groups for total body potassium). Low density lipoprotein cholesterol decreased in the GH-treated group (P < 0.05) only. Carotid intima media thickness was significantly greater (P < 0.05) in the untreated group than in the GH-treated group. Assessment of psychological well-being using the Nottingham Health Profile revealed improvement in overall score, energy levels, and emotional reaction in the GH-treated group compared with those in the untreated group (P < 0.02). In conclusion, GH treatment for 10 yr in GHD adults resulted in increased lean body and muscle mass, a less atherogenic lipid profile, reduced carotid intima media thickness, and improved psychological well-being.

Adult↗
PubMed1993

Detection of thirty-second cognitive activations in single subjects with positron emission tomography: a new low-dose H2(15)O regional cerebral blood flow three-dimensional imaging technique.

Positron emission tomography regional CBF (rCBF) studies of cognitive processes have traditionally required 30-60 mCi of H2(15)O per scan and intersubject averaging to achieve statistical significance. However, intersubject anatomical, functional, and disease variability can make such an approach problematic. A new method that produces significant results in single subjects is presented. It is based upon high-sensitivity three-dimensional imaging and a "slow" bolus administration of < 15 mCi of H2(15)O per scan. The method is validated in four normal volunteers using control and auditory-language activation tasks with four scans per condition and statistical parametric mapping analysis. It is demonstrated that the rCBF distribution associated with the cognitive state is detected during the arrival of radiotracer in the brain. This occurs over 30 s and constitutes a critical temporal window during which stimulation should be performed. A 90-s acquisition time is found to produce results of greater significance than a 60-s acquisition time. The implications of the results and the functional neuroanatomical findings are discussed. This method is suitable for the study of individual functional neuroanatomy in many neuropsychological, pharmacologic, and symptom states in normal subjects and in patients with psychiatric and neurologic disorders.

Adult↗
PubMed1989

Evaluation of PET count rate performance.

A proposal is made for the test conditions to evaluate PET count rate performance. This performance depends in a complex manner on the spatial distribution of activity and scattering material. Therefore, a combined body phantom is proposed, which is as simple as possible but which adequately simulates the range of clinical application of a whole body tomograph. Taking into account the special properties of the new block detector design, a comprehensive test procedure is developed. This includes not only the common count rate characteristic, but also checks for the accuracy of randoms estimation and count loss correction schemes, and for the occurrence of pulse pile up. This is done for different source and scatter configurations, simulating brain, cardiac, and abdominal imaging, respectively. Examples are given, based on measurements of the latest generation PET scanners, namely the CT1 PT 931/08-12 and the Scanditronix PC 2048-07WB.

Models, Structural↗
PubMed1989

Quality control procedures in positron tomography.

The derivation of physiological parameters in positron tomography relies on accurate calibration of the tomograph. Normally, the calibration relates image pixel count density to the count rate from an external blood counter per unit activity concentration in each device. The quality control of the latter is simple and relies on detector stability assessed by measurement of a standard source of similar geometry to a blood sample. The quality control of the tomographic data depends on (i) detector stability, (ii) uniformity of calibration and normalisation sources and (iii) reproducibility of the attenuation correction procedure. A quality control procedure has been developed for an 8 detector ring (15 transaxial plane) tomograph in which detector response is assessed by acquiring data from retractable transmission ring sources. These are scanned daily and a print out of detector efficiencies is produced as well as changes from a given date. This provides the raw data from which decisions on recalibration or renormalization are made.

Quality Control↗
PubMed1989

Aspects of three dimensional reconstruction for a multi ring positron tomograph.

An important feature of multi ring positron tomographs is the inter plane septa, the purpose of which is to reduce random and scattered coincidences. In general, such septa also eliminate the coincidence lines of response between pairs of detectors more than one ring apart. The operation of a camera without septa must result in an increase not only in the true coincidence rate, but also in the singles, and therefore in the dead time and randoms rate, and in the scattered coincidences. A configuration option in the coincidence hardware of the 8 ring, 15 slice ECAT 931/08-12 enables a full set of 64 sinograms to be acquired when the septa are removed. The detector normalisation and transmission data for studies with the septa out can be obtained using a rotating pin source. To take maximum advantage of the additional signal, the emission data must be reconstructed using a fully three dimensional reconstruction algorithm. This paper presents an analysis of some phantom studies acquired without septa and reconstructed in three dimensions. The results are compared with data acquired with septa for the same phantoms imaged under similar conditions. It is found that, with the septa removed, the signal to noise for a uniform, 20 cm diameter cylinder improves by a factor of 2.8 in the centre of the field of view, whereas in regions distant from the centre in the axial direction, the signal to noise decreases due to the increase in scatter and randoms. An improvement in signal to noise is observed in 6 cm of the 10 cm axial length of the tomograph.

Image Processing, Computer-Assisted↗
PubMed1989

Measurement of resolution and recovery in recent generation positron tomographs.

In positron tomographic images, the ability to differentiate closely lying structures, the spillover of activity from a region into adjacent regions and the reduction in apparent isotope concentration in small structures are all dependent on spatial resolution. Resolution in the reconstructed image is affected by (i) detector size, (ii) the spatial sampling used (e.g. stationary, wobble), (iii) the amount of smoothing in the reconstruction process (or subsequent to reconstruction) and (iv) the image pixel size. Under ideal conditions, modern commercial tomographs can produce a reconstructed spatial resolution of 5 mm or less. However, this is rarely realizable in a clinical study due to the inadequacy of counting statistics and the amplification of statistical noise. In practice, a smoother filter has to be used. This paper presents a summary of practical measurements of spatial resolution, and the related count recovery, performed on recent generation positron tomographs. It is intended to contribute to the definition of methods of measuring these parameters which is part of an on going concerted action in positron tomography supported by the European Commission.

Image Processing, Computer-Assisted↗
PubMed1987

Beneficial effect of nitrates on myocardial glucose utilization in unstable angina pectoris.

Myocardial uptake of the glucose analog F-18-2-fluoro-2-deoxy-D-glucose (FDG) was assessed by positron emission tomography in 6 normal volunteers, 7 patients with chronic stable angina and 22 patients with unstable angina at rest in fasting conditions. Regional myocardial perfusion was assessed by rubidium-82. The study was repeated a few days later after intravenous infusion of isosorbide dinitrate. FDG uptake was similar in control subjects and patients with stable angina (0.023 +/- 0.032 vs 0.012 +/- 0.008 mol/ml/min, p less than 0.42) but was about 4-fold higher on the average in patients with unstable angina (0.084 +/- 0.047, p less than 0.01). The severity of coronary obstructions in stable and unstable angina patients was similar. The increased uptake involved the whole heart, including areas not distal to critically stenosed vessels; it was not associated with reduced myocardial perfusion and was not related to a recent episode of transient ischemia as assessed by symptoms and by Holter monitoring. After continuous infusion of nitrates, FDG uptake was consistently and significantly reduced toward normal levels both in areas perfused by critically stenosed coronary arteries and by noncritically stenosed vessels.

Adult↗
PubMed1986

Myocardial glucose utilization in ischaemic heart disease: preliminary results with F18-fluorodeoxyglucose and positron emission tomography.

Regional myocardial utilization of glucose can be assessed non-invasively in man with the sugar analogue F18-2-fluoro-2-deoxyglucose (FDG) and positron emission tomography (PET). The preliminary observations made in patients with different clinical forms of ischaemic heart disease using FDG and PET are reported. In patients with stable angina pectoris at rest, regional myocardial glucose utilization was comparable to that in normal volunteers whilst an increased utilization of glucose was found in the recovery from exercise-induced ischaemia in the regions that showed an abnormal perfusion during the stress test. These metabolic changes persisted in the recovery phase when all the parameters that were altered during the exercise, including myocardial perfusion, had normalized. In patients with unstable angina, characterized by repeated episodes of spontaneous ST depression, myocardial glucose utilization was regionally or globally increased already at rest in the absence of symptoms or signs of ischaemia at the time of study and most often without evident perfusion abnormalities. In patients with a recent infarction, two different patterns of glucose utilization in the infarcted area have been described: a concordant decrease of myocardial perfusion and glucose utilization; a disproportionately increased glucose utilization relative to perfusion interpreted as an index of the presence of ischaemic, but still viable myocardium.

Angina Pectoris↗
PubMed1986

Increased uptake of 18F-fluorodeoxyglucose in postischemic myocardium of patients with exercise-induced angina.

Regional myocardial perfusion and exogenous glucose uptake were assessed with rubidium-82 (82Rb) and 18F-2-fluoro-2-deoxyglucose (FDG) in 10 normal volunteers and 12 patients with coronary artery disease and stable angina pectoris by means of positron emission tomography. In patients at rest, the myocardial uptake of 82Rb and FDG did not differ significantly from that measured in normal subjects. The exercise test performed within the positron camera in eight patients produced typical chest pain and ischemic electrocardiographic changes in all. In each of the eight patients a region of reduced cation uptake was demonstrated in the 82Rb scan recorded at peak exercise, after which uptake of 82Rb returned to the control value 5 to 14 min after the end of the exercise. In these patients, FDG was injected in the recovery phase when all the variables that were altered during exercise, including regional myocardial 82Rb uptake, had returned to control values. In all but one patient, FDG accumulation in the regions of reduced 82Rb uptake during exercise was significantly higher than that in the nonischemic regions, i.e., the ones with a normal increment of 82Rb uptake on exercise. In the nonischemic areas, FDG uptake was not significantly different from that found in normal subjects after exercise. In conclusion, myocardial glucose transport and phosphorylation seem to be enhanced in the postischemic myocardium of patients with exercise-induced ischemia.

Adult↗
PubMed1986

Prolonged metabolic recovery allows late identification of ischemia in the absence of electrocardiographic and perfusion changes in patients with exertional angina.

Regional myocardial perfusion and exogenous glucose uptake were assessed in 10 normal subjects and 10 patients with coronary artery disease and stable angina pectoris using 82Rubiduim and 18F-2-fluoro-2-deoxyglucose with positron emission tomography. At rest regional myocardial perfusion and glucose uptake in patients were comparable with those in normals. In 7 patients and 5 normals a supine bicycle exercise test was performed within the positron camera. In all 7 patients, exercise induced typical chest pain and ischemic electrocardiographic changes accompanied by regional abnormalities of myocardial perfusion which normalized 5 to 14 minutes after the end of exercise. In these patients 18F-2-fluoro-2-deoxyglucose was injected during recovery from exercise when all the parameters that were altered during the test, including myocardial perfusion, were back to control. In all 7, glucose uptake in the regions which showed abnormal perfusion during exercise was significantly higher than in the non ischemic regions (i.e. the ones with a normal increment of 82Rubidium uptake during exercise). In 2 patients the test was repeated on a different day and 18F-2-fluoro-2-deoxyglucose was injected during exercise in the presence of frank ischemia. In contrast to the injection following exercise, in both patients, glucose uptake in the ischemic region was found to be lower than in the non ischemic ones. In conclusion, in patients recovering from exercise-induced ischemia exogenous glucose utilization is enhanced in the previously ischemic myocardium. This occurs in the absence of symptoms and electrocardiographic changes and allows the identification and location of previous myocardial ischemia.

Angina Pectoris↗
PubMed1980

Long-term clearance of [57Co]cyanocobalamin in vegans and pernicious anaemia.

1. Whole-body counting has been used to monitor the clearance of [57Co]cyanocobalamin in normal subjects, vegans and patients with pernicious anaemia. After oral administration of 57Co-labelled cyanocobalamin (1 microgram/1 muCi), subjects were counted for radioactivity monthly for a maximum period of 1 year. 2. The results obtained were consistent with a monoexponential clearance model and a least squares fit showed that there was no significant difference between the mean clearance rates for the vegans and normal subjects. 3. The patients with pernicious anaemia cleared the vitamin significantly more quickly than the normal control subjects. 4. This may be due to failure to reabsorb biliary vitamin B12 in pernicious anaemia because of the absence of intrinsic factor.

Adolescent↗
PubMed1977

Non-stedy-state studies of low-density-liproprotein turnover in familial hypercholesterolaemia.

1. The non-steady-state turnover of low-density lipoprotein (LDL), labelled in its apoprotein moiety (apo-B) with 131I, was determined in four patients with familial hypercholesterolaemia, three of them homozygotes. 2. The fractional and absolute catabolic rates (FCR and ACR) of LDL-apo-B were determined by relating the excretion of radioactivity, measured in urine in vitro and by whole-body counter in vivo, to plasma radioactivity and to LDL specific radioactivity respectively. 3. The FCR remained relatively constant, even after marked reduction of LDL pool size by means of plasma exchange. This confirms the existence of an intrinsic defect in LDL catabolism in familial hypercholesterolaemia. 4. LDL-apo-B synthesis, determined by summing the ACR and the daily increment in plasma LDL, was much higher in the three homozygotes than in the one heterozygote, in whom the synthetic rate was normal. 5. These results illustrate the usefulness of combining plasma exchange and whole-body radioactivy counting as a means of examining the relationship between the turnover and pool size of a 131I-labelled protein, such as LDL.

Adolescent↗