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Biomedical subjects

M A Lodge

Publications and source records attributed to M A Lodge.

9 recordsLinked to original sources
PubMed2000

Differences in skeletal kinetics between vertebral and humeral bone measured by 18F-fluoride positron emission tomography in postmenopausal women.

We have sought to investigate regional differences in skeletal kinetics between lumbar vertebrae and the humerus of postmenopausal women with 18F-fluoride positron emission tomography (PET). Twenty-six women, mean age 62 years, had dynamic PET scans of the lumbar spine and lower humerus after the injection of 180 MBq 18F-fluoride ion. Plasma arterial input functions (IFs) were calculated from a mean IF measured arterially from 10 women and scaled according to late individual venous activity. Vertebral and humeral time activity curves were measured by placing regions of interest (ROI) over lumbar vertebrae and the humeral shaft. Using a three-compartmental model and nonlinear regression analysis the macroconstant Ki, representing plasma clearance of fluoride to bone mineral, and the individual rate constants K1 (related to regional skeletal blood flow) and k2 to k4 describing transport between plasma, an extracellular fluid compartment and a bone mineral compartment, were measured. Mean vertebral Ki (3.47x10(-2) ml x min(-1) x ml(-1)) and K1 (1.08x10(-1) ml x min(-1) x ml(-1)) were found to be significantly greater than humeral Ki (1.64x10(-2) ml min(-1) ml(-1); P<0.0001) and K1 (3.90x10(-2) ml x min(-1) x ml(-1); P<0.0001) but no significant differences were found in k2, k3, and k4. These findings confirm differences in regional skeletal kinetics between lumbar vertebrae and the lower humerus. These observations may help increase our understanding of the regional differences in pathophysiology and response to treatment that have been observed in sites consisting predominantly of either trabecular or cortical bone. 18F-fluoride PET may prove to be a valuable technique in the noninvasive measurement of regional skeletal metabolism.

Adult↗
PubMed2000

Parametric images of blood flow in oncology PET studies using [15O]water.

UNLABELLED: PET was used to measure tumor blood flow, which is potentially valuable for diagnosis and assessing the effects of therapy. To help visualize regional differences in blood flow and to improve the accuracy of region-of-interest placement, a parametric imaging approach was developed and compared with the standard region-of-interest method. METHODS: Five patients with renal cell metastases in the thorax were studied using [15O]water and dynamic PET. To assess the reproducibility of the blood flow measurements, multiple water studies were performed on each patient. Model fitting was done on a pixel-by-pixel basis using several different formulations of the standard single-compartment model. RESULTS: The tumors studied spanned a wide range of blood flows, varying from 0.4 to 4.2 mL/min/g. These values were generally high compared with those of most other tissues, which meant that the tumors could be readily identified in parametric images of flow. The different model formulations produced images with different characteristics, and no model was entirely valid throughout the field of view. Although tumor blood flow measured from the parametric images was largely unbiased with respect to a standard regional method, large errors were observed with certain models in regions of low flow. The most robust model throughout the field of view had only 1 free parameter and, compared with a regional method, gave rise to a flow bias of 0.3%+/-3.1% for tumor and 16%+/-11% for low-flow soft tissue (muscle plus fat). With this model, tumor blood flow was measured with an SD of 7.6%+/-4.0%. CONCLUSION: Parametric imaging provides a convenient way of visualizing regional changes in blood flow, which may be valuable in studies of tumor blood flow.

Blood Flow Velocity↗
PubMed1999

A PET study of 18FDG uptake in soft tissue masses.

A study was performed with the aim of investigating some of the methodological factors affecting the ability of quantitative 2-[18F]-fluoro-2-deoxy-d-glucose (FDG) positron emission tomography to assess tumour malignancy. Twenty-nine patients with soft tissue masses were studied using a 6-hour scanning protocol and various indices of glucose metabolism were compared with histological grade. Significant differences were observed in the time-activity response of benign and high-grade tumours. High-grade sarcomas were found to reach a peak activity concentration approximately 4 h after injection whereas benign lesions reached a maximum within 30 min. This translated to improved differentiation between these two tumour types using a standard uptake value (SUV) derived from images acquired at later times. An SUV measured 4 h post-injection was found to be as useful an index of tumour malignancy as the metabolic rate of FDG determined using either Patlak or non-linear regression techniques. Each of these indices had a sensitivity and specificity of 100% and 76% respectively for the discrimination of high-grade sarcomas from benign tumours.

Case-Control Studies↗
PubMed1999

Non-invasive assessment of skeletal kinetics using fluorine-18 fluoride positron emission tomography: evaluation of image and population-derived arterial input functions.

To measure regional skeletal kinetics using fluorine-18 fluoride positron emission tomography (PET) it is necessary to know the concentration of radioactive tracer being delivered to bone by arterial plasma with relation to time, the arterial input function (IFa). Methods by which IFa can be derived without arterial sampling are attractive because of their relative technical simplicity and the reduction in possible morbidity to the subject. We have compared the use of a scaled population input function (IFp) and a corrected image-derived input function from the aorta (IFi) with an IFa directly measured from a radial artery line in ten normal postmenopausal women. Both of the aforementioned methods rely only on a small number of discrete venous samples. Each subject had a dynamic PET acquisition of the lumbar spine performed after the intravenous injection of 180 MBq (18)F-fluoride. Both the IFp and the IFi were compared with the IFa in terms of the accuracy of determination of six parameters. These were: plasma clearance of fluoride to bone mineral (K(i)), unidirectional plasma clearance to total bone tissue (K(1)) and individual rate constants k(2), k(3) and k(4), calculated using non-linear regression with a three-compartment model, and the plasma clearance to bone mineral calculated using the Patlak method (K(pat)). For both the IFp and the IFi method the root mean square errors for K(pat) and K(i) were similar and small (<8.2%). The errors in determining K(1) and the rate constants k(2) to k(4) are larger by either method, but with a small advantage using the IFp method. It is concluded that the use of either non-invasive method for determining the arterial plasma input function is suitable for the measurement of the most important parameters, K(i) and K(pat), in these subjects.

Female↗
PubMed1999

Prospective evaluation of soft tissue masses and sarcomas using fluorodeoxyglucose positron emission tomography.

BACKGROUND: The differentiation of soft tissue sarcoma (STS) from benign masses is difficult owing to their clinical and radiological similarities. Accurate staging is hindered by the large number of sites at which metastases may be found. This study examined the value of whole-body [18F]2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG PET) in patients presenting with soft tissue masses. METHODS: Thirty patients with a soft tissue mass suspected to be malignant were evaluated with FDG PET. The images were evaluated qualitatively and quantitatively for uptake of FDG to determine whether benign lesions could be differentiated from malignant tumours, and for the presence of metastases. RESULTS: Thirty-one masses were removed from 30 patients; 12 were benign and 19 were malignant STSs. Using qualitative assessment of the FDG PET images, all the high-grade STSs (n = 12) were correctly identified, but low-grade STS (n = 7) could not be differentiated from a benign lesion. Using a quantification assessment, there was a 95 per cent sensitivity and a 75 per cent specificity in diagnosing STS. Three patients had metastases at presentation; two were correctly identified by FDG PET. CONCLUSION: FDG PET has a role in distinguishing high-grade STS from low-grade or benign STS and may have a role in staging malignant tumours.

Adolescent↗
PubMed1998

A clinical evaluation of the quantitative accuracy of simultaneous emission/transmission scanning in whole-body positron emission tomography.

We present a clinical evaluation of the quantitative bias which is introduced during simultaneous emission/transmission (SET) acquisition for the application of whole-body positron emission tomography (PET) with fluorine-18 2-fluoro-2-deoxy-d-glucose. The quantitative accuracy of the SET technique was assessed by means of a clinical study involving 28 patients and a realistic phantom experiment. In the clinical study, SET overestimated the activity concentration in the tumours by a factor of approximately 1.10, but in the phantom study, where the tumours were smaller, the bias was found to increase to a value of 1.39. The bias in the soft tissue regions of the patient studies varied between 1.03 and 1.36, and close agreement was observed with the corresponding phantom results. The extent of the bias increased as the local activity concentration decreased and we attribute the effect to scattered photons from the transmission source which are detected in the emission window during SET.

Artifacts↗
PubMed1998

Algorithms for calculating detector efficiency normalization coefficients for true coincidences in 3D PET.

Accurate normalization of lines of response in 3D PET is a prerequisite for quantitative reconstruction. Most current methods are component based, calculating a series of geometric and intrinsic detector efficiency factors. We have reviewed the theory behind several existing algorithms for calculating detector efficiency factors in 2D and 3D PET, and have extended them to create a range of new algorithms. Three of the algorithms described are 'fully 3D' in that they make use of data from all detector rings for the calculation of the efficiencies of any one line of response. We have assessed the performance of the new and existing methods using simulated and real data, and have demonstrated that the fully 3D algorithms allow the rapid acquisition of crystal efficiency normalization data using low-activity sources. Such methods enable the use of scatter-free scanning line sources or the use of very short acquisitions of cylindrical sources for routine normalization.

Algorithms↗
PubMed1995

The experimental evaluation of a prototype rotating slat collimator for planar gamma camera imaging.

A collimator consisting of a series of parallel slats has been constructed and used in conjunction with a conventional gamma camera to collect one-dimensional projections of the radioisotope distribution being imaged. With the camera remaining stationary, the collimator was made to rotate continuously over the face of the detector and the projections acquired were used to reconstruct a planar image by the theory of computed tomography. The propagation of noise on image reconstruction was largely offset by the increased geometric efficiency that resulted from the enlarged solid angle of acceptance afforded by the slat collimator. For a uniform disc of activity the signal to noise ratio (SNR) at a point in an image reconstructed by convolution and backprojection is shown to be given by [formula:see text] and Q1(xi) is the one-dimensional filter function in Fourier space. Improved noise behaviour was observed for images acquired with the slat collimator compared to those acquired with a low-energy high-resolution (LEHR) collimator for small distributions of activity. Spatial resolution with the slat collimator was approximately equal to that obtained with an LEHR collimator and improved contrast was observed in images of small hot regions.

Biophysical Phenomena↗