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Biomedical subjects

P Niemi

Publications and source records attributed to P Niemi.

At least 19 recordsLinked to original sources
PubMed2003

Correlation of transthoracic Doppler echocardiography and magnetic resonance imaging in measuring left anterior descending artery flow velocity and time-course of dipyridamole-induced coronary flow increase.

There is an increasing need for new, functional and more quantitative parameters to assess coronary arterial function, for the purposes of evidence-based medicine. Coronary arterial function has been widely studied using pharmacological stimulation induced by dipyridamole or adenosine. Coronary flow reserve (CFR), defined as the ratio of pharmacologically induced hyperemic flow divided by basal flow, has been found to be an important functional index in both the clinical and subclinical stages of cardiovascular diseases. Ten healthy male volunteers were studied to compare transthoracic Doppler echocardiography (TTE) and MRI for measuring left anterior descending coronary artery (LAD) flow velocity and CFR. Additionally, the time-response curve of dipyridamole infusion was studied in five healthy males using TTE. Assessment of blood flow velocity, measured as MDV, PDV and VTI indicated Pearson's correlation coefficients of 0.88, 0.85 and 0.70, respectively, between flow velocity measurements performed using TTE and MRI. The results indicate that, despite minor differences in LAD diastolic velocities measured by TTE and MRI, the correlation of the LAD diastolic velocities measured using both methods are good and both methods are feasible for measuring CFR. Moreover, TTE has the unique capability of continuous measurement of LAD flow velocity, which allowed assessment of the time-response curve for dipyridamole-induced increase in LAD flow velocity in this study. This study indicates that the TTE method may be used in sequential or on-line monitoring of LAD blood flow velocity and therefore can be applied to evaluate the time- or dose-response effects of infused drugs in the coronary circulation of humans.

Adult↗
PubMed2002

Severe somatization in women is associated with altered cerebral glucose metabolism.

BACKGROUND: Somatization is a clinical phenomenon characterized by multiple, medically unexplained somatic symptoms. The pathophysiology remains unknown. We aimed to test the hypothesis of a central nervous system dysfunction in the pathophysiology of this disorder. METHOD: We studied 10 female patients diagnosed as having somatization disorder or undifferentiated somatoform disorder with no current Axis I disorders according to DSM-IV. They were compared with 17 healthy female volunteers using brain [18F]-fluorodeoxyglucose-PET with MRI reference. RESULTS: The patients had lower cerebral metabolism rates of glucose (P<0.05) in both caudate nuclei, left putamen and right precentral gyrus compared with healthy volunteers. CONCLUSIONS: This is the first study to demonstrate changes in brain metabolism in somatizing women. The regional cerebral hypometabolism is probably associated with the pathophysiology of somatization.

Adult↗
PubMed2002

Decreased large artery distensibility in borderline hypertension is related to increased in vivo low-density lipoprotein oxidation.

The present study tested the hypothesis that reduced arterial elasticity seen in hypertension is related to increased oxidation of LDL. Fifteen men with borderline hypertension (BHT), with blood pressure values classified as high normal (systolic blood pressure 130-140 mmHg or diastolic blood pressure 85-89 mmHg) were included. The control group comprised 22 men with normal blood pressure values (<135/80 mmHg) matched for age, body size and LDL-cholesterol level. Distensibility of aorta was measured using magnetic resonance imaging, and distensibility of the common carotid artery using ultrasound. Baseline LDL diene conjugation was used as a marker for ox-LDL. Aortic and carotid distensibilities were lower in the BHT men than in controls (1.4 +/- 0.6 vs. 1.9 +/- 0.6%/10 mmHg, p<0.05 for aortic distensibility; 2.9 +/- 0.9 vs. 3.6 +/- 0.6%/10 mmHg, p<0.05 for carotid distensibility). Ox-LDL was significantly higher in the BHT men than in controls (44 +/-15 vs. 28 +/- 8 micromol/L, p<0.01). In univariate analysis, ox-LDL associated with aortic distensibility (r=-0.43, p<0.05). In multivariate analysis, the differences in distensibilities between the groups disappeared when the values were adjusted for ox-LDL. These data show decreased arterial elasticity and increased LDL oxidation in young men with borderline hypertension, and suggest that oxidative modification of LDL particles may play a pathophysiological role in the development of reduced arterial distensibility in hypertension.

Adult↗
PubMed2001

Global myocardial blood flow and global flow reserve measurements by MRI and PET are comparable.

Coronary flow reserve (CFR) measurements have been widely used in assessing the functional significance of coronary artery stenosis because they are more sensitive in predicting major cardiac events than angiographically detected reductions of coronary arteries. Myocardial blood flow can be determined by measuring coronary sinus (CS) flow with velocity-encoded cine magnetic resonance imaging (VEC-MRI). The purpose of this study was to compare global myocardial blood flow (MBF) and CFR measured using VEC-MRI with MBF and CFR measured using positron emission tomography (PET). We measured MBF at baseline and after dipyridamole-induced hyperemia in 12 male volunteers with VEC-MRI and PET. With VEC-MRI, MBF was 0.64 +/- 0.09 (ml/min/g) at baseline and 1.59 +/- 0.79 (ml/min/g) at hyperemia, which yielded an average CFR of 2.51 +/- 1.29. With PET, MBF was 0.65 +/- 0.20 (ml/min/g) at baseline and 1.78 +/- 0.72 (ml/min/g) at hyperemia, which yielded an average CFR of 2.79 +/- 0.97. The correlation of MBFs between these two methods was good (r = 0.82, P < 0.001). The CFRs measured by MRI correlated well with those measured using PET (r = 0.76, P < 0.004). These results suggest that MRI is a useful and accurate method to measure global MBF and CFR. Therefore, it would be suitable for studying risk factor modifications of vascular function at an early stage in healthy volunteers.

Adult↗
PubMed2001

Coronary flow reserve: measurement with transthoracic Doppler echocardiography is reproducible and comparable with positron emission tomography.

Detection of early vascular changes indicated by lowered coronary flow reserve (CFR) would allow early treatment and prevention of atherosclerosis. The purpose of this study was to test whether it is possible to reproducibly measure CFR with transthoracic Doppler echocardiography (TTE) in healthy volunteers. We measured CFR using dipyridamole infusion in ten healthy male volunteers with two methods: TTE and positron emission tomography (PET) with oxygen-15-labelled water (group A). However, CFR was assessed twice with TTE in eight healthy male volunteers (group B) to study the reproducibility of this method. We compared CFRs obtained using TTE flow measurements in the left anterior descending coronary artery (LAD) and PET flow measurements in the corresponding myocardial area. Coronary flow in LAD could be measured in all subjects using TTE. By TTE, an average CFR based on peak diastolic flow velocity (PDV) was 2.72 +/- 1.16, mean diastolic flow velocity (MDV) 2.56 +/- 1.06 and velocity time integral (VTI) 1.87 +/- 0.49. The results were reproducible in two repeated TTE studies (coefficient of variation in MDV 6.1 +/- 4.3%, n=8). By PET, CFR was 2.52 +/- 0.84. CFR assessed by TTE correlated closely with that measured by PET (MDV r=0.942, P<0.001; PDV r=0.912, P<0.002 and VTI r=0.888, P<0.006) and intraclass correlation was 0.929 (MDV) and tolerance limits for differences of CFRs was -0.78 to 0.72. We show that CFR measured by TTE has an excellent correlation with CFR measured by PET. We also found that TTE measurements of CFR were highly reproducible.

Adolescent↗
PubMed2001

Assessing coronary sinus blood flow in patients with coronary artery disease: a comparison of phase-contrast MR imaging with positron emission tomography.

OBJECTIVE: This study was performed to determine whether MR imaging can be used to reliably measure global myocardial blood flow and coronary flow reserve in patients with coronary artery disease as compared with such measurements obtained by positron emission tomography (PET). SUBJECTS AND METHODS: We measured myocardial blood flow first at baseline and then after dipyridamole-induced hyperemia in 20 patients with coronary artery disease. Myocardial blood flow as revealed by MR imaging was calculated by dividing coronary sinus flow by the left ventricular mass. Coronary flow reserve was calculated by dividing the rate of hyperemic flow by the rate of baseline flow. RESULTS: Using MR imaging, myocardial blood flow at baseline was 0.73 +/- 0.23 mL x min(-1) x g(-1), and at hyperemia the blood flow was 1.43 +/- 0.37 mL x min(-1) x g(-1), yielding an average coronary flow reserve of 1.99 +/- 0.47. Using PET, myocardial blood flow was 0.89 +/- 0.21 mL x min(-1) x g(-1) at baseline and 1.56 +/- 0.42 mL x min(-1) x g(-1) at hyperemia, yielding an average coronary flow reserve of 1.77 +/- 0.36. The correlation of myocardial blood flow and coronary flow reserve measurements for these two methods was an r of 0.80 (p < 0.01) and an r of 0.50 (p < 0.05), respectively. CONCLUSION: This study shows that myocardial blood flow measurements obtained using MR imaging have a good correlation with corresponding PET measurements. Coronary flow reserve measurements obtained using MR imaging had only moderate correlation with PET-obtained measurements. Our results suggest that MR imaging flow quantification could potentially be used for measuring global myocardial blood flow in patients in whom interventional treatment for coronary artery disease is being evaluated.

Adult↗
PubMed2000

A multicenter validation of an active contour-based left ventricular analysis technique.

Quantitative analysis of functional cardiac magnetic resonance (MR) images has been limited by the lack of well-validated, semiautomatic, methods for rapid analysis. We describe the evaluation of a DICOM-compatible PC-based parallel-processing tool, for cardiac magnetic resonance analysis (CAMRA), which supports semiautomatic image mensuration using an active contour model-based algorithm. The CAMRA software was used to analyze data from 12 patients in a multicenter acquisition and analysis trial to compare semiautomatic contour detection with manual planimetry of the left ventricular endocardium from short-axis, breath-held, cine gradient-echo images. There was excellent agreement between the manual and semiautomatic measurements of global left ventricular function, with no significant (P = 0.32) difference in the determination of ejection fraction (-0.9 +/- 3.1% [mean difference +/- 1 standard deviation]). There was no significant interobserver difference in the semiautomatically measured ejection fraction. Additionally, a single observer completed the analysis on data from 30 patients and found no significant (P = 0.05) difference in the determination of ejection fraction (-1.3 +/- 3.5% [mean difference +/- 1 standard deviation]). The CAMRA software demonstrates the capability for the reproducible evaluation of global left ventricular function in cardiac patients, with adequate interobserver reproducibility for use in multicenter trials.

Adult↗
PubMed2000

Wheat or rye supplemented diets do not affect faecal mucus concentration or the adhesion of probiotic micro-organisms to faecal mucus.

In a crossover study, volunteers consumed a diet supplemented with either wheat or rye bread. Levels of faecal mucus were determined and the adhesion of five selected probiotics to immobilized intestinal mucus, was assessed. No significant difference in the concentration of faecal mucus or adhesion of the probiotics to the mucus was observed during the two dietary periods. However, male subjects were observed to excrete significantly more mucus during the rye bread supplemented diet. From these observations it was concluded that these two diets, with a low or high fibre content, did not change the potential binding sites for the tested probiotics or affect the level of mucus excreted in the faeces, however, on a high fibre diet men excrete more faecal mucus.

Bacterial Adhesion↗
PubMed2000

Multimodality MR imaging assessment of myocardial viability: combination of first-pass and late contrast enhancement to wall motion dynamics and comparison with FDG PET-initial experience.

PURPOSE: To combine three magnetic resonance (MR) imaging modalities-dobutamine stress cine, first pass, and late contrast material-enhanced T1-weighted imaging-and to compare the results with 2-[fluorine 18]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) in the assessment of unviable myocardium in coronary artery disease. MATERIALS AND METHODS: Ten patients with multivessel coronary artery disease underwent MR imaging before and 6 months after bypass surgery. Left ventricular cine MR imaging was performed at rest and during dobutamine infusion. Inversion-recovery gradient-echo images were obtained to study myocardial contrast enhancement at first pass and 5 minutes later. FDG PET was performed with orally administered acipimox before surgery. RESULTS: With dobutamine cine MR imaging, unviable myocardium was detected with a sensitivity of 79% and a specificity of 93%; postoperative wall thickening was the standard. First-pass analysis increased these values to 97% and 96%; analysis of late enhancement with T1-weighted imaging, to 62% and 98%. FDG PET had a sensitivity of 81% and a specificity of 86%. CONCLUSION: The combination of first-pass enhancement analysis and wall motion assessment with stress significantly increases the specificity of MR imaging in the detection of unviable sectors.

Aged↗
PubMed2000

Assessment of coronary flow reserve using fast velocity-encoded cine MR imaging: validation study using positron emission tomography.

OBJECTIVE: Previous studies using intravascular Doppler sonography and positron emission tomography (PET) have shown that the hemodynamic significance of coronary artery stenosis can be evaluated by measuring coronary flow reserve. The purpose of this study was to assess whether MR imaging measurements of coronary flow reserve in the left anterior descending artery are comparable with those obtained with PET in the corresponding territory. SUBJECTS AND METHODS: MR imaging and PET flow measurements were obtained in 10 healthy volunteers. Blood flow velocity in the left anterior descending artery was measured with breath-hold velocity-encoded cine MR imaging before and after IV administration of dipyridamole. The coronary flow velocity reserve measured by MR imaging was compared with the myocardial perfusion reserve in the anterior myocardium quantified on using PET and (15)O-labeled water. RESULTS: The average flow velocity reserve in the left anterior descending artery measured on MR imaging was 2.44+/-1.14 in healthy volunteers, which was comparable with the myocardial perfusion reserve measured by PET (2.52+/-0.84). MR imaging and PET measurements of the coronary flow reserve showed a significant correlation (r = 0.79, p<0.01). CONCLUSION: MR imaging measurement of the flow velocity reserve in the proximal left anterior descending artery correlates well with the myocardial perfusion reserve obtained with PET and (15)O-labeled water.

Adult↗
PubMed1999

The normal faecal microflora does not affect the adhesion of probiotic bacteria in vitro.

Adhesion of probiotic microorganisms to the intestinal mucosa is considered important for many of the reported health effects. The influence of the endogenous microflora on the adhesion of four probiotic lactobacilli to immobilised intestinal mucus was investigated. It was observed that pre-treatment of the immobilised mucus with faecal extract slightly increased the adhesion of Lactobacillus GG. Pre-treatment of the immobilised mucus with faecal bacteria did not affect the adhesion of the tested strains. These results suggest that the normal microflora may not greatly affect the initial adhesion of the probiotic bacteria. This validates the results of earlier reports where the influence of the normal microflora was not taken into account.

Adult↗
PubMed1999

Large-artery elastic properties in young men : relationships to serum lipoproteins and oxidized low-density lipoproteins.

Measures of arterial elasticity have been proposed as surrogate markers for asymptomatic atherosclerosis. We investigated the relations of serum lipoproteins, oxidized low-density lipoprotein (ox-LDL), and familial hypercholesterolemia (FH) to arterial elasticity among young men. As a marker of arterial elasticity we measured compliance in the thoracic aorta by using magnetic resonance imaging and in the common carotid artery by using ultrasound. LDL diene conjugation was used as a marker of ox-LDL. In study I, 25 healthy men (aged 29 to 39) were classified into 2 extreme groups according to previously measured high-density lipoprotein cholesterol to total cholesterol ratio (HDL-C/TC ratio). In study II, the healthy men were used as controls for 10 age matched asymptomatic patients with FH. In healthy men, the group with low HDL-C/TC ratio had decreased carotid artery compliance (2. 3+/-0.4% versus 1.9+/-0.5%/10 mm Hg, P=0.034). In univariate analysis, the compliance of the carotid artery associated with ox-LDL (r =-0.49, P=0.016) and HDL-C/TC ratio (r=0.41, P=0.040). In multivariate regression analyses, ox-LDL was the only independent determinant for compliance of the carotid artery (P=0.016). Aortic elasticity was not related to standard lipid variables, but the compliance of the ascending aorta associated with ox-LDL (r=-0.44, P=0.030). In FH patients, arterial elasticity was similar to that in controls. We conclude that elasticity of the common carotid artery is affected by serum lipid profile in young men. The current study demonstrates for the first time an in vivo association between ox-LDL and arterial elasticity suggesting that oxidative modification of LDL may play a role in the alteration of arterial wall elastic properties.

Adult↗
PubMed1998

Imaging perfusion deficits in ischemic heart disease with susceptibility-enhanced T2-weighted MRI: preliminary human studies.

AIM: This feasibility study explores relative myocardial perfusion characterization with an investigational T2/T2 contrast agent. METHODS: Dysprosium-DTPA bis (methylamide) was administered peripherally in six patients with thallium defects. Rest and stress multi-section, gated, T2-weighted images were acquired with a 1.5 T echo-planar imager. Change in transverse relaxation rate was calculated in four segments for each subject. RESULTS: Magnetic resonance (MR) identified five of five instances of ischemia or infarction, at a dose of agent (0.25 mmol/kg) that was comparable to that currently used with clinically approved gadolinium agents. Injection at twice this dose resulted in saturation of the signal change, and the one ischemic segment corresponding to the higher dose was not identified by MR. MR was negative in two segments which, on final diagnosis, were determined to manifest thallium attenuation artifact. CONCLUSION: MR perfusion imaging with high susceptibility agents has the potential to characterize myocardial perfusion deficits.

Adult↗
PubMed1998

The effect of paramagnetic contrast media on T1 relaxation times in brain tumors.

PURPOSE: To study T1 relaxation times in brain tumors before and after paramagnetic contrast medium injection. MATERIAL AND METHODS: Seventeen patients with a known or suspected brain tumor were studied with an echo planar inversion recovery imaging sequence using 10 different inversion times. Double injections of Gd chelate (0.1 mmol/kg + 0.2 mmol/kg) were administered in 5 patients, and a single 0.2-mmol/kg dose in 12 patients. RESULTS: After the 0.2-mmol/kg dose, T1 decreased from 1121 +/- 130 ms to 987 +/- 103 ms in gray matter (p < 0.001), and from 666 +/- 29 ms to 646 +/- 27 ms in white matter (p < 0.001). Tumor T1 shortened from 1515 +/- 319 ms to 717 +/- 383 ms. After the 0.1-mmol/kg dose (n = 5), tumor T1 decreased from 1116 +/- 261 ms to 793 +/- 202 ms and after the additional 0.2-mmol/kg dose it decreased further to 526 +/- 141 ms. CONCLUSION: Postcontrast T1 relaxation times in tumors showed considerable variation and remained, on average, relatively long compared to white matter. This should be taken into account when deciding which pulse sequences, imaging parameters, and contrast agent doses are optimal for brain tumor imaging.

Adult↗
PubMed1998

Reading and writing difficulties do not always occur as the researcher expects.

Making a prognosis about reading and learning difficulties is a tricky business, even if a large array of relevant variables is taken into account. The present article discusses such an endeavour, on the basis of a longitudinal four-year study which started with an orthodox intervention on linguistic awareness. However, after initial success, new groups of reading, writing and math disabled children were identified in the course of years. Membership of these groups could not always be predicted on the basis of extensive cognitive diagnostics performed during the preschool. Rather, the pupil's adaptive behaviour while coping with the demands of school work emerges as an important prognostic factor. This was particularly evident in an interaction combining math and reading comprehension in grade 3.

Agraphia↗
PubMed1996

Myocardial intensity changes associated with flow stimulation in blood oxygenation sensitive magnetic resonance imaging.

Functional magnetic resonance imaging exploits deoxygenated blood as an endogenous source for contrast in assessing local changes in tissue perfusion. Intrinsic changes in myocardial signal intensity were measured during dipyridamole induced coronary vasodilatation with T2*-weighted echo planar MRI in healthy volunteers. Concurrently, changes in flow velocity in the left anterior descending coronary artery were measured using a time-of-flight method. Dipyridamole infusion produced 14 +/- 6% increase in myocardial signal intensity (n = 7). Temporal profile of the myocardial signal intensity changes correlated well with the augmentation of coronary flow velocity. The data are consistent with the concept that changes in myocardial deoxyhemoglobin content due to altered flow result in changes in magnetic susceptibility that can be detected on T2*-weighted MR images.

Adult↗