Biomedical subjects

Stig A Larsson

Publications and source records attributed to Stig A Larsson.

25 records · Page 2Linked to original sources

PubMed2003

Positron flight in human tissues and its influence on PET image spatial resolution.

The influence of the positron distance of flight in various human tissues on the spatial resolution in positron emission tomography (PET) was assessed for positrons from carbon-11, nitrogen-13, oxygen-15, fluorine-18, gallium-68 and rubidium-82. The investigation was performed using the Monte Carlo code PENELOPE to simulate the transport of positrons within human compact bone, adipose, soft and lung tissue. The simulations yielded 3D distributions of annihilation origins that were projected on the image plane in order to assess their impact on PET spatial resolution. The distributions obtained were cusp-shaped with long tails rather than Gaussian shaped, thus making conventional full width at half maximum (FWHM) measures uncertain. The full width at 20% of the maximum amplitude (FW20M) of the annihilation distributions yielded more appropriate values for root mean square addition of spatial resolution loss components. Large differences in spatial resolution losses due to the positron flight in various human tissues were found for the selected radionuclides. The contribution to image blur was found to be up to three times larger in lung tissue than in soft tissue or fat and five times larger than in bone tissue. For (18)F, the spatial resolution losses were 0.54 mm in soft tissue and 1.52 mm in lung tissue, compared with 4.10 and 10.5 mm, respectively, for (82)Rb. With lung tissue as a possible exception, the image blur due to the positron flight in all human tissues has a minor impact as long as PET cameras with a spatial resolution of 5-7 mm are used in combination with (18)F-labelled radiopharmaceuticals. However, when ultra-high spatial resolution PET cameras, with 3-4 mm spatial resolution, are applied, especially in combination with other radionuclides, the positron flight may enter as a limiting factor for the total PET spatial resolution--particularly in lung tissue.

Adipose Tissue↗

PubMed2003

A new approach for improving diagnostic accuracy in Alzheimer's disease and frontal lobe dementia utilising the intrinsic properties of the SPET dataset.

Alzheimer's disease (AD) and frontal lobe dementia (FLD) show characteristic patterns of regional cerebral blood flow (rCBF). However, these patterns may overlap with those observed in the aging brain in elderly normal individuals. The aim of this study was to develop a new method for better classification and recognition of AD and FLD cases as compared with normal controls. Forty-six patients with AD, 7 patients with FLD and 34 normal controls (CTR) were included in the study. rCBF was assessed by technetium-99m hexamethylpropylene amine oxime and a three-headed single-photon emission tomography (SPET) camera. A brain atlas was used to define volumes of interest (VOIs) corresponding to the brain lobes. In addition to conventional image processing methods, based on count density/voxel, the new approach also analysed other intrinsic properties of the data by means of gradient computation steps. Hereby, five factors were assessed and tested separately: the mean count density/voxel and its histogram, the mean gradient and its histogram, and the gradient angle co-occurrence matrix. A feature vector concatenating single features was also created and tested. Preliminary feature discrimination was performed using a two-sided t-test and a K-means clustering was then used to classify the image sets into categories. Finally, five-dimensional co-occurrence matrices combining the different intrinsic properties were computed for each VOI, and their ability to recognise the group to which each individual scan belonged was investigated. For correct classification of the AD-CTR groups, the gradient histogram in the parieto-temporal lobes was the most useful single feature (accuracy 91%). FLD and CTR were better classified by the count density/voxel histogram (frontal and occipital lobes) and by the mean gradient (frontal, temporal and parietal lobes, accuracy 98%). For AD and FLD the count density/voxel histogram in the frontal, parietal and occipital lobes classified the groups with the highest accuracy (85%). The concatenated joint feature correctly classified 96% of the AD-CTR, 98% of the FLD-CTR and 94% of the AD-FLD cases. 5D co-occurrence matrices correctly recognised 98% of the AD-CTR cases, 100% of the FLD-CTR cases and 98% of the AD-FLD cases. The proposed approach classified and diagnosed AD and FLD patients with higher accuracy than conventional analytical methods used for rCBF-SPET. This was achieved by extracting from the SPET data the intrinsic information content in each of the selected VOIs.

Aged↗

PubMed2003

Visualisation of the normal adrenals at SPET examination with 111In-pentetreotide.

On single-photon emission tomography (SPET) examinations with indium-111 pentetreotide, we have often observed a small "hot" spot close to the upper portion of the left kidney. While it was initially believed that this represented a tumour in the tail of the pancreas or in the left adrenal, we now understand that it represents normal adrenal uptake. Since the adrenals have not been described as normally visualised, this uptake may interfere with the interpretation of the examination. We have studied how often the normal adrenals are visualised at such examinations. One hundred consecutive clinical (111)In-pentetreotide examinations in adults including SPET of the abdomen and with normal findings were studied. All examinations with a hot spot attributable to the adrenals were, when available, compared with computed tomography (CT) or magnetic resonance imaging (MRI) of the abdomen performed on clinical grounds within 3 months before or at any time after the scintigraphy. In 11 patients both adrenals were visualised. In 27 patients only the left and in one only the right adrenal was visualised. CT or MRI examinations were available for comparison in 25 of these 39 patients. Two of these showed a pathological finding in the left adrenal. A conservative interpretation is that the normal adrenal is visualised on one or both sides in at least one-quarter of adults at SPET examination with (111)In-pentetreotide.

Adolescent↗

PubMed2003

99mTc-sestamibi uptake and histological malignancy grade in invasive breast carcinoma.

The aim of this study was to investigate whether there is a correlation between (99m)Tc-sestamibi uptake and histological malignancy grade in breast carcinoma. Such a correlation could, prior to surgery and histopathological analysis, facilitate selection of patients who need adjuvant therapy. Ninety-six patients with mammographically determined lesions and/or a palpable tumour suspected for malignancy underwent (99m)Tc-sestamibi scintimammography prior to surgery. The final diagnosis was determined by histopathological examination. Benign lesions, cancer in situ and tumours located medially in the breast were excluded. Fifty-three invasive cancer lesions in 53 patients were finally included in the study. Planar scintigraphic breast imaging included two prone lateral projections and one anterior supine projection taken 10 min after injection of 700 MBq (99m)Tc-sestamibi. Focal (99m)Tc-sestamibi uptake in breast lesions was used as the scintigraphic criterion of abnormality. Tumour to background ratios were calculated with partial volume compensation, and histological malignancy grading was performed according to the Elston classification. A correlation was found between (99m)Tc-sestamibi uptake and histological malignancy grade in invasive breast carcinomas ( P<or=0.037).

Adult↗

PubMed2002

A novel quantitative dual-isotope method for simultaneous ventilation and perfusion lung SPET.

A quantitative dual-isotope single-photon emission tomography (SPET) technique for the assessment of lung ventilation (V) and perfusion (Q) using, respectively, technetium-99m labelled Technegas (140 keV) and indium-113m labelled macro-aggregated albumin (392 keV), is presented, validated and clinically tested in a healthy volunteer. In order to assess V, Q and V/Q distributions in quantitative terms, algorithms which correct for down scattering, photon scattering and attenuation, as well as an organ outline algorithm, were implemented. Scatter and down-scatter correction were made in the spatial domain by pixel-wise image subtraction of projection-dependent global scattering factors obtained from the energy domain. The attenuation correction was based on an iterative projection/back-projection method. All studies were made on a three-headed SPET system (Trionix) with medium-energy parallel-hole collimators. The set of input data for quantification was based on SPET acquisition of emission data in four separate energy windows, the associated cumulative energy spectra and transmission data. The attenuation correction routine as well as the edge detection algorithm utilized data from (99m)Tc transmission tomography. Attenuation data for (113m)In were obtained by linear scaling of the (99m)Tc attenuation maps. The correction algorithms were experimentally validated with a stack phantom system and applied on a healthy volunteer. The mean difference between the corrected SPET data of the dense stack lung phantom and those obtained from the corresponding scatter- and attenuation-"free" version was only 1.9% for (99m)Tc and 0.9% for (113m)In. The estimated fractional V/Q distribution in the 3-D lung phantom volume had its peak at V/Q=1, with a width (FWHM) of 0.31 due to noise, particularly in the (113m)In images, and to partial volume effects. For a healthy volunteer, the corresponding values were 0.9 and 0.35, respectively. This method allows accurate assessment of radionuclide distribution on a regional basis. For basic lung physiology and clinical practice, the method allows assessment of the global frequency functions of the V, Q and V/Q distributions.

Algorithms↗

PubMed2002

No effect of drains on the postoperative hematoma volume in hip replacement surgery: a randomized study using scintigraphy.

In a prospective randomized study we used erythrocyte scintigraphy to evaluate whether drainage reduced the hematoma volume after total hip arthroplasty. 12 patients were left without drains and 10 patients had two drains inserted, one below the fascia and one subcutaneously. We used tomographic registration (SPECT) to calculate the volume of the hematoma (erythrocytes) about 22 hours after surgery and found that drainage did not reduce the volume, but increased the need for blood transfusion.

Aged↗

PubMed2001

Regional cerebral blood flow as assessed by principal component analysis and (99m)Tc-HMPAO SPET in healthy subjects at rest: normal distribution and effect of age and gender.

The increasing implementation of standardisation techniques in brain research and clinical diagnosis has highlighted the importance of reliable baseline data from normal control subjects for inter-subject analysis. In this context, knowledge of the regional cerebral blood flow (rCBF) distribution in normal ageing is a factor of the utmost importance. In the present study, rCBF was investigated in 50 healthy volunteers (25 men, 25 women), aged 31-78 years, who were examined at rest by means of single-photon emission tomography (SPET) using technetium-99m d, l-hexamethylpropylene amine oxime (HMPAO). After normalising the CBF data, 27 left and 27 right volumes of interest (VOIs) were selected and automatically outlined by standardisation software (computerised brain atlas). The heavy load of flow data thus obtained was reduced in number and grouped in factors by means of principal component analysis (PCA). PCA extracted 12 components explaining 81% of the variance and including the vast majority of cortical and subcortical regions. Analysis of variance and regression analyses were performed for rCBF, age and gender before PCA was applied and subsequently for each single extracted factor. There was a significantly higher CBF on the right side than on the left side ( P<0.001). In the overall analysis, a significant decrease was found in CBF ( P=0.05) with increasing age, and this decrease was particularly evident in the left hemisphere ( P=0.006). When gender was specifically analysed, CBF was found to decrease significantly with increasing age in females ( P=0.037) but not in males. Furthermore, a significant decrease in rCBF with increasing age was found in the brain vertex ( P=0.05), left frontotemporal cortex ( P=0.012) and temporocingulate cortex ( P=0.003). By contrast, relative rCBF in central structures increased with age ( P=0.001). The ability of standardisation software and PCA to identify functionally connected brain regions might contribute to a better understanding of the relationships between rCBF at rest, anatomically defined brain structures, ageing and gender.

Adult↗