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Biomedical subjects

A Jackson

Publications and source records attributed to A Jackson.

At least 127 records · Page 7Linked to original sources
PubMed2000

Parametric mapping of scaled fitting error in dynamic susceptibility contrast enhanced MR perfusion imaging.

The purpose of this study was to examine the benefits of routine generation of a parametric image of scaled curve fitting errors in the analysis of dynamic susceptibility contrast enhanced MR perfusion imaging. We describe the scaled fitting error (SFE), which reflects the magnitude of potential errors in the estimation of perfusion parameters from dynamic susceptibility contrast enhanced studies. The SFE is the root-mean-square error between the observed values in the time course of change of effective transverse relaxation rate (delta R2* (t)) in tissue and the theoretical values derived by gamma variate curve fitting, scaled with a simple function related to the area under the fitted gamma variate curve. The SFE was tested using Monte Carlo simulation and by observations in normal volunteers and patients. This demonstrated that the SFE was linearly related to uncertainties in calculation of the values of relative cerebral blood volume (rCBV) and relative mean transit time (rMTT). High spatial resolution SFE maps were obtained in all volunteers and patients. In normal brain, SFE was consistently higher in white matter than in grey matter. In 54/85 patients with neurodegenerative or vascular brain disease, SFE maps showed focal areas with high values owing to poor signal to noise ratio in delta R2*(t). Increased SFE was also found in 11/54 brain tumours owing to loss of conformance of delta R2*(t) to the gamma variate function. SFE mapping is simple to implement and the computational overhead is negligible. It is concluded that parametric maps of SFE allow visual and quantitative comparison of fitting errors with the theoretical gamma variate model between anatomical regions and provide a quality control device to rapidly assess the reliability of the associated rCBV and rMTT estimations.

Adult↗
PubMed2000

Treating internal resorption using a syringeable composite resin.

BACKGROUND: Internal resorption is a pathological process initiated within the pulp space with the loss of dentin. It often is described as an oval shaped enlargement of the root canal space and usually is asymptomatic and detectable by routine radiographs. Treatment of internal resorption has included several materials--gutta-percha, zinc oxide eugenol and amalgam alloy. These materials do not provide strength to the tooth structure. CASE DESCRIPTION: A 29-year-old woman was referred to a dental clinic for treatment of a large internal resorptive defect in the coronal and middle one-third of the maxillary left central incisor root with no apparent periapical pathosis, as well as a large periapical radiolucency at the apex of the maxillary left lateral incisor that was associated with a necrotic pulp. The authors used a dual-cure syringable composite resin in conjunction with a bonding agent within the defect to treat it. CLINICAL IMPLICATIONS: This technique seals the dentinal tubules and strengthens the remaining tooth structure. It also improves the outcome of resorptive defects and reduces operators' chair time.

Adult↗
PubMed2000

The factor V R2 allele: risk of venous thromboembolism, factor V levels and resistance to activated protein C.

Case-control studies have yielded conflicting results regarding the relative risk of venous thromboembolism associated with the factor V R2 allele. We calculated odds ratios in 581 patients and 469 age-matched controls. The odds ratio for the R2 allele in patients relative to controls was 1.21 (95% CI 0.84 to 1.74). These results do not support the hypothesis that the R2 allele is a risk factor for venous thromboembolism. There was no relationship between factor V levels and R2 carrier status. Normalised APC sensitivity ratios were not lower in carriers of the R2 allele. In an in vitro model progressive APC resistance was observed with factor V levels of 60% and less but ratios less than 2.4 (equivalent to a normalised ratio of 0.73) did not occur until factor V levels were less than 20%. The relationship between APC resistance and factor V level was not observed in a factor VIII-independent model.

Activated Protein C Resistance↗
PubMed2000

The transfer of 15N from urea to lysine in the human infant.

To explore the nutritional significance of urea hydrolysis for human subjects, male infants being treated for severe undernutrition were given oral doses of 10 mg [15N15N]urea every 3 h for 36 h, on admission, during rapid growth and after repletion with either moderate or generous intakes of protein. Urea hydrolysis was calculated from the 15N enrichment of urinary urea, and where possible, lysine, alanine, glycine and histidine were isolated from urine by preparative ion-exchange chromatography for measurement of 15N enrichment. Sufficient N was obtained for 15N enrichment of lysine to be measured on fifteen occasions from six children. Urea hydrolysis accounted for half of all urea production with 130 (SD 85) mg N/kg hydrolysed per d, most of which appeared to be utilized in synthetic pathways. Of the samples analysed successfully, nine samples of lysine were enriched with 15N (mean atom percent excess 0.0102, range 0.0017-0.0208) with relative enrichment ratios with respect to lysine of 1.63 (range 0.18-3.15), 1.96 (range 0.7-3.73) and 0.9 (range 0.4-1.8) for glycine, alanine and histidine respectively. Enriched samples were identified at each treatment phase and 68% of the variation in lysine enrichment was explained by the variation in urea enrichment with 54% explained by the overall rate of delivery of 15N to the lower gastrointestinal tract. The results indicate a minimum of 4.7 mg lysine per kg body weight made available by de novo synthesis with the more likely value an order of magnitude higher. Thus, urea hydrolysis can improve the quality of the dietary protein supply by enabling an increased supply of lysine and other indispensable amino acids.

Alanine↗
PubMed2000

The role of MR angiography in the pretreatment assessment of intracranial aneurysms: a comparative study.

BACKGROUND AND PURPOSE: With developments in coil technology, intracranial aneurysms are being treated increasingly by the endovascular route. Endovascular treatment of aneurysms requires an accurate depiction of the aneurysm neck and its relation to parent and branch vessels preoperatively. Our goal was to estimate the clinical efficacy of MR angiography (MRA) in the pretreatment assessment of ruptured and unruptured intracranial aneurysms. We compared MRA source data (axial acquired partitions), multiplanar reconstruction (MPR) of these data, as well as maximum intensity projection (MIP) and 3D-isosurface images with intraarterial digital subtraction angiography (IA-DSA). METHODS: The study was performed in 29 patients with 42 intracerebral aneurysms. The MRA data were examined in four different forms--as axial source data, MPR images of the source data, and MIP and 3D isosurface--rendered images. A composite standard of reference for each aneurysm was then constructed using this information together with the IA-DSA findings by looking at aneurysm detection rate, aneurysm morphology, neck interpretation, and branch vessel relationship to the aneurysm. All techniques, including conventional IA-DSA, were then scored independently on a five-point scale from 1 (non diagnostic) to 5 (excellent correlation with the standard of reference) for each of the aneurysm components as compared with the composite picture. An overall score for each technique was also obtained. RESULTS: Of the 42 aneurysms examined, 34 were small (<10 mm), six were large (10-25 mm), and two were giant (>25 mm). Three aneurysms were not detected with MRA. These were smaller than 3 mm and either in an anatomically difficult location (middle cerebral artery bifurcation) or obscured by adjacent hematoma. Two large aneurysms were depicted as undersized by IA-DSA owing to the presence of intramural thrombus shown by MRA axial source data. IA-DSA received the highest scores overall and in three of the four subgroups. Three-dimensional isosurface reconstructions scored higher than did IA-DSA for depiction of the aneurysm neck, although this difference was not significant. The MPR and 3D-isosurface images were comparable to those of IA-DSA in all categories. MPR images were particularly useful for defining branch vessels and the aneurysm neck. MIP images scored poorly in all subgroups (P < .005) compared with IA-DSA findings, except for in aneurysm detection. Source data images were significantly inferior to those of IA-DSA in all categories (P < .005). CONCLUSION: MRA is currently inferior to IA-DSA in pretreatment assessment of intracranial aneurysms, and can miss small lesions (<3 mm). It can, however, provide complementary information to IA-DSA, particularly in anatomically complex areas or in the presence of intramural thrombus. If MRA is used in aneurysm assessment, a meticulous technique with reference to both axial source data and MPR is mandatory. The axial source data should not be interpreted in isolation. Three-dimensional isosurface images are comparable to those of IA-DSA and are more reliable than are MIP images, which should be interpreted with caution.

Adult↗
PubMed2000

Observations on the first year: a commentary.

Physician-assisted suicide has been incorporated into the end-of-life care continuum responsibility in Oregon. Because systems for end-of-life care were well established before the implementation of the Death with Dignity Act, potential problems with the law have been anticipated and prevented or diverted. Hospice services and comfort care are accessible throughout Oregon. Hospice care is offered to terminally ill Oregonians and their families without regard to an individual's intent to ask, or not ask, his or her doctor for a lethal prescription. No Oregonian has to choose between hospice and physician-assisted suicide.

Hospices↗
PubMed1999

Long term tolerance of high dose three-dimensional conformal radiotherapy in patients with localized prostate carcinoma.

BACKGROUND: The current study was undertaken to evaluate the incidence and predictors of late toxicity in patients with localized prostate carcinoma treated with high dose three-dimensional conformal radiotherapy (3D-CRT). METHODS: A total of 743 patients with prostate carcinoma classified as T1c-T3 were treated with 3D-CRT that targeted the prostate and seminal vesicles. A minimum tumor dose of 64.8 gray (Gy) was given to 96 patients (13%), 70.2 Gy to 266 patients (365), 75.6 Gy to 320 patients (43%), and 81.0 Gy to 61 patients (8%). The median follow-up time was 42 months (range, 18-109 months). Late toxicity was graded according to the Radiation Therapy Oncology Group morbidity scoring scale. RESULTS: Late gastrointestinal (GI) and urinary (GU) toxicities were absent or minimal (Grade 0 or 1) in 90% of patients. The 5-year actuarial likelihood of the development of Grade 2 and 3 late GI toxicities was 11% and 0.75%, respectively. A multivariate analysis identified doses > or =75.6 Gy (P<0.001), history of diabetes mellitus (P = 0.01), and the presence of acute GI symptoms during treatment (P = 0.02) as independent predictors of Grade > or =2 late GI toxicity. The 5-year actuarial likelihood of the development of Grade 2 and 3 late GU toxicities was 10% and 3%, respectively. Doses > or =75.6 Gy (P = 0.008) and acute GU symptoms (P<0.001) were independent predictors of Grade > or =2 late GU toxicity. Among 544 patients who were potent before treatment (73% of all patients), 211 (39%) became impotent after 3D-CRT. The 5-year actuarial risk of potency loss was 60%. Doses > or =75.6 Gy (P<0.001) and the use of neoadjuvant androgen deprivation (P = 0.01) were independent predictors of posttreatment erectile dysfunction. CONCLUSIONS: The incidence of severe late complications after high dose 3D-CRT was minimal. Radiation doses > or =75.6 Gy and the presence of acute treatment-related symptoms during 3D-CRT correlated with a higher incidence of Grade > or =2 late GI and GU toxicities. In addition to higher doses, the use of androgen deprivation therapy increased the likelihood of permanent impotence in these patients. Intensity-modulated radiotherapy, which makes it possible to enhance the conformality of the dose distribution, has recently been implemented in an attempt to reduce the incidence of moderate grade toxicities in patients receiving high dose 3D-CRT.

Adenocarcinoma↗
PubMed1999

Neuroepithelial bodies as airway oxygen sensors.

Since the discovery of neuroepithelial bodies (NEB) in the late 1930s, evidence has accumulated to suggest that these cells may function as hypoxia-sensitive airway sensors. Until recently, this hypothesis was based largely on morphological observations. The use of in vitro models of isolated NEB, combined with electrophysiological approaches, have provided direct evidence that NEB cells express a membrane-bound O2 sensor and are the transducers of hypoxic stimulus. Here, we review the historical evidence and current state of knowledge of the oxygen-sensing properties of NEB cells, comparison with other O2 sensing cells, as well as recent advances that have been made using molecular and electrophysiological techniques. The possible role of NEB in perinatal pulmonary pathophysiology is also discussed.

Animals↗
PubMed1999

The differentiation of DSM-III-R psychotic depression in later life from nonpsychotic depression: comparisons of brain changes measured by multispectral analysis of magnetic resonance brain images, neuropsychological findings, and clinical features.

BACKGROUND: Psychotic depression has been proposed as a distinct subtype of major depression. There is considerable evidence for this in younger patients, although the neuroimaging has been rudimentary. Volumetric imaging studies are required of consecutive cohorts of patients with depression. METHODS: Ninety-nine consecutive elderly patients were diagnosed with DSM-III-R major depression. Eighteen were psychotic, and 81 were not. Sixty-six patients were given a neuropsychological test battery, and 44 had a magnetic resonance imaging brain scan. A model integrating clinical, psychological, and neuroimaging findings for the explanation of delusion formation during depression is proposed. RESULTS: Psychotic depression was characterized by worse physical health, more family history of depression, a poorer response to antidepressant drugs, and more severe lowering of mood; however, the strongest predictors of the presence of delusions were diencephalic atrophy, reticular activating system lesions, brain stem atrophy, and left-sided frontotemporal atrophy. The psychotic patients had poorer performance on tests of frontal lobe function and mental processing speed. CONCLUSIONS: In the elderly, psychotic depression is etiologically, clinically, and neuroradiologically distinct, and has different treatment requirements, from nonpsychotic major depression.

Age Factors↗
PubMed1999

A fast model independent method for automatic correction of intensity nonuniformity in MRI data.

A novel nonparametric approach for correcting intensity nonuniformity in magnetic resonance (MR) images is described. This approach is based solely on the assumption that the various sources of nonuniformity in MR imaging give rise to smooth variations in image intensity, and that these variations can be extracted and corrected for. The advantage of this computationally fast method is that it can be applied early in quantitative analysis while being independent of pulse sequence and is insensitive to pathological processes. This algorithm has been tested on both simulated and real data. Application to tissue segmentation and functional MR imaging has shown a marked improvement in quantitative analysis. J. Magn. Reson. Imaging 1999;10:550-562.

Algorithms↗
PubMed1999

Improved quality of re-sliced MR images using re-normalized sinc interpolation.

This article shows that re-normalizing the interpolation kernel for a constant integral can make a significant improvement in performance of sinc interpolation methods. A comparison was performed between standard and re-normalized sinc kernels of various sizes using data from four commonly used magnetic resonance (MR) imaging sequences. Standard rotations were performed and compared with a "gold standard" data set generated by use of a large (13 x 13 x 13) sinc kernel. Measurements of systematic pixel intensity offset error and variance of generated residuals were used to estimate resultant interpolation error. Theoretical estimates of the consequent savings in computation time were compared with the measured time required for each algorithm and with the automated image registration (AIR) program. The use of a small (5 x 5 x 5) re-normalized kernel produced relative errors comparable to those in the gold standard data set, allowing saving in computation time of up to 30 times in comparison with standard sinc interpolation. This approach brings the implementation of MR volume re-slicing much closer to the demands of a clinical environment. J. Magn. Reson. Imaging 1999;10:582-588.

Brain↗
PubMed1999

Peripheral blood allogeneic microchimerism in lung and cardiac allograft recipients.

We have been investigating two parameters, donor antigen-specific hyporeactivity and peripheral blood allogeneic microchimerism, to determine whether these parameters will predict a chronic rejection-free state and which recipients may be candidates for steroid withdrawal. We have identified donor antigen-specific hyporeactivity for 33% (16/48) of lung and 23% (11/47) of heart recipients. For both organ groups, the hyporeactive subgroup experienced a lower incidence of chronic rejection. The probability of donor antigen-specific hyporeactivity predicting a chronic rejection-free state is 100% for lung and 91% for heart recipients. We have identified peripheral blood allogeneic microchimerism for 77% (20/26) of lung and 36% (9/25) of heart recipients tested at 12-18 months posttransplant. Donor antigen-specific hyporeactivity correlates with a critical level of donor cells in lung recipients; the probability of high peripheral blood allogeneic microchimerism levels predicting a chronic rejection-free state in lung recipients is 100%. The results in heart recipients are not as clear with a short-, but not long-term, trend of higher chimerism levels correlating with the development of donor antigen-specific hyporeactivity. These results illustrate the usefulness of immmune parameters to predict long-term graft outcome in an organ-specific manner.

Bronchiolitis Obliterans↗
PubMed1999

Reduced efficacy of 8-OH-DPAT's inhibition of lordosis behavior by prior estrogen treatment.

The effects of bilateral VMN infusion with the 5-HT1A receptor agonist, (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 200, 1000, or 2000 ng), on lordosis behavior were examined in hormonally primed ovariectomized rats. When rats were given a single injection with 25 microg estradiol benzoate followed 48 h later with 500 microg progesterone, inhibition of lordosis behavior was evident at all doses of 8-OH-DPAT. However, when rats were treated with 25 microg estradiol benzoate followed 7 days later with a second injection of 25 microg estradiol benzoate and then progesterone, none of the doses of 8-OH-DPAT effectively inhibited lordosis behavior. In some rats, cannulae were located near the most rostral portion of the VMN. In these rats, there was no effect of the second estrogen treatment on the response to 8-OH-DPAT. Therefore, a second experiment was performed to specifically evaluate the effects of two estradiol benzoate treatments on the response to bilateral 8-OH-DPAT infusion in the rostral VMN. In contrast to the reduced effectiveness of the 8-OH-DPAT infusion in the mid to caudal VMN in rats given two injections with estradiol benzoate, 2000 ng 8-OH-DPAT continued to effectively inhibit lordosis behavior following the 5-HT1A receptor agonist's infusion into the more rostral areas. These findings are discussed in relation to earlier studies in which the potency, but not the efficacy, of 8-OH-DPAT was reduced following systemic treatment with the 5-HT1A receptor agonist.

8-Hydroxy-2-(di-n-propylamino)tetralin↗