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F T Jensen

Publications and source records attributed to F T Jensen.

At least 37 records · Page 2Linked to original sources
PubMed1995

Evaluation of transfusional iron overload before and during iron chelation by magnetic resonance imaging of the liver and determination of serum ferritin in adult non-thalassaemic patients.

The ability to quantitate transfusional iron overload is crucial for determining the need for and the efficacy of chelation therapy in patients with long-standing transfusion-dependent anaemias. We evaluated the usefulness of some indirect measures of iron overload in estimating the iron concentration in the liver--the most important iron storage organ--in 26 non-chelated adult non-thalassaemic patients. Liver iron concentration was determined non-invasively by magnetic resonance imaging (MRI). The standard error of the estimated liver iron concentration was 80 mumol Fe/g dried liver tissue when using the number of transfused blood units, and 93 mumol Fe/g when using a serum ferritin assay. Follow-up in 11 patients (12-48 months) revealed that serum ferritin is a poor measure of the liver iron concentration during iron chelation. However, this discrepancy was individually different and seemed to be dependent on the erythropoietic marrow activity. By monitoring the liver iron concentration by MRI, we compared the efficacy of chelation with desferrioxamine given either by subcutaneous continuous infusions or by bolus injections. Depletion of liver iron stores could be achieved efficiently by both regimens.

Adolescent↗
PubMed1994

A comparison of the effects of oestrogen/progestogen, high-dose oral calcium, intermittent cyclic etidronate and an ADFR regime on calcium kinetics and bone mass in postmenopausal women with spinal osteoporosis.

The effects of four different treatments for osteoporosis were compared in a prospective, randomized, 3-year study in 74 postmenopausal women with spinal crush fracture osteoporosis. Patients were randomly assigned to cyclic oestrogen/progestogen therapy (group 1, n = 20), a daily oral calcium dose of 2 g (group 2, n = 17), intermittent cyclic etidronate therapy (group 3, n = 19), or an ADFR treatment with triiodothyronine as activator and etidronate as depressor (group 4, n = 18). Spine and forearm bone mineral content was measured before entry and every 30 weeks. Combined calcium balance and 47Ca kinetic studies were performed before and after 1 and 3 years of treatment. Bone turnover, estimated by serum alkaline phosphatase and renal hydroxyproline excretion, decreased in all four groups during the first half of the treatment period but remained reduced during the second half in groups 1 and 3 only. Group 1 had a significantly positive calcium balance after 60 weeks of treatment. After 150 weeks, the positive effect on calcium balance was significant and greater in groups 1 and 3 than in the other groups. This was achieved by a greater reduction in resorption rate in group 1 at week 60 and in groups 1 and 3 at week 150 as compared with the other groups. Only group 1 had a significant increase in spinal bone mass while a decrease in bone mass at the distal forearm was observed in the etidronate-treated group. We conclude that treatment of postmenopausal osteoporosis with oestrogen/progestogen for 3 years results in net spinal bone gain and a positive effect on calcium balance slightly better than that of intermittent etidronate. These effects were inferior in the groups receiving a large calcium supplementation or the ADFR group where no change in calcium balance or bone mass was found.

Administration, Oral↗
PubMed1994

Precision, accuracy, and image plane uniformity in NMR relaxation time imaging on a 1.5 T whole-body MR imaging system.

In order to evaluate the accuracy, precision and image plane uniformity a phantom study was undertaken on a 1.5 T whole-body MR imaging system (Philips Gyroscan S15 HP). The manufacturers algorithm for obtaining relaxation time images was used. This method uses Ratios and Least Squares (RLSQ-algorithm) on data obtained from a combination of a multi-echo (CPMG) and an inversion recovery pulse sequence, yielding a calculated T1-, T2- and a proton density image simultaneously. T1 and T2 accuracy was measured in phantoms consisting of CuSO4 and MnCl2 in aqueous solution in different concentrations. The results were compared to a reference T1 and T2 obtained by spectroscopy. The accuracy error over the entire relaxation time range was expressed as the root mean square of the modulus of the difference between the reference and the image measurement and was 2.3% for T1 and 4.1% for T2. Precision or reproducibility was measured by 11 double estimations on 11 samples. The precision error was 0.35% for both T1 and T2. Image plane uniformity, i.e., the homogeneity of pixel values throughout the image plane, was measured by 3 consecutive image readings from a phantom of 19 cm in diam. in 8 directions 45 degrees apart and 1, 3, 5, 7, 9 cm from the center. Errors in the imaging plane were expressed as the deviation from the center value. For both T1 and T2 the maximum deviation was less than 5% over the entire image in the transverse plane. It is concluded that when the pulse sequence timings are carefully optimized, the mixed imaging sequence in combination with the RLSQ algorithm used in this MRI system is a reliable and precise means of obtaining relaxation time data.

Algorithms↗
PubMed1994

Non-invasive assessment of tissue iron overload in the liver by magnetic resonance imaging.

We investigated the clinical usefulness of a standard magnetic resonance imaging (MRI) system for non-invasive determination of the liver iron concentration in 38 patients with iron overload and 15 normal controls by measurement of the signal intensity ratio between liver and skeletal muscle (SIR). However, SIR was found dependent on the applied repetition time (TR) of the MRI system, which led us to investigate this relationship in autopsy material of liver and muscle tissue specimens with various iron content. Based on these results, adjustment of SIR measurements to a constant value of TR was achieved. By use of this technique we found a close correlation between MRI and chemically determined liver iron concentration (r2 = 0.98) as well as the serum ferritin concentration (r2 = 0.86). The reproducibility was sufficiently good for the use of MRI in the follow-up of iron reductive treatment. The use of iron store parameters in serum was found insufficient as indicators of endpoint for venesection therapy, if 20 mumol Fe/g dry weight was applied as the upper reference limit of the liver iron concentration. It is concluded that MRI based on SIR measurements offers a precise and reproducible non-invasive method for the determination and follow-up of iron overload within a wide range of liver iron concentrations. Our findings may increase the clinical use of MRI in haematological patients with iron overload.

Bloodletting↗
PubMed1994

The effect of iron overload and iron reductive treatment on the serum concentration of carbohydrate-deficient transferrin.

The concentration of carbohydrate-deficient transferrin in serum (CDT) has been used as a reliable indicator of recent alcohol consumption. We have investigated the utility of this laboratory test in 20 patients with hereditary haemochromatosis (HH) by simultaneous evaluation of serum concentrations of liver transaminases, gamma-glutamyl transpeptidase, iron, transferrin and assessment of the liver iron concentration by magnetic resonance imaging. 11 patients were re-examined during iron depletion with phlebotomies. In all 11 patients intensive but not maintenance iron removal was associated with an increase in serum CDT, in three patients even to levels above the reference range. The mean serum CDT increased from 8.5 (SD 2.2) U/l to 16.6 (SD 7.2) U/l (P < 0.001). Iron mobilization from the liver was found particularly responsible for the increase in serum CDT. Independent of this finding we found a significant semi-logarithmic correlation (r = -0.77, P = 0.009) between the MRI determined liver iron concentration and serum CDT in the patients not on iron depletion. Our findings indicate that the utility of serum CDT as a measure of alcohol consumption in patients with HH may be compromised, especially during intensive iron depletion.

Adult↗
PubMed1993

Heart transplantation in a case of juvenile hereditary haemochromatosis followed up by MRI and endomyocardial biopsies.

Cardiac involvement in hereditary haemochromatosis (HH) is a poor prognostic sign and is the main cause of death in the juvenile form. The treatment of choice is iron removal therapy by phlebotomy, but treatment by iron chelation (desferrioxamine) has been recommended in cases with severe cardiac symptoms. We describe here the first case of juvenile HH undergoing heart transplantation, which became necessary despite intensive iron removal therapy by phlebotomy and treatment by desferrioxamine. Throughout the course the myocardial iron content was monitored by endomyocardial biopsies and by magnetic resonance imaging (MRI). At the last follow-up, 18 months after transplantation, the myocardial iron content in the transplanted heart was still within reference ranges by biochemical determination and MRI and the patient's condition was completely satisfactory. In conclusion, heart transplantation should be considered in cases of severe juvenile HH. In the follow-up of these patients MRI may be a useful supplement.

Adult↗
PubMed1993

Nasal airway geometry: comparison between acoustic reflections and magnetic resonance scanning.

To evaluate the accuracy of the acoustic reflection (AR) technique for determination of nasal cavity cross-sectional areas, the area-distance function of both sides of the nose was determined in 10 subjects and compared with magnetic resonance imaging (MRI). Interindividual variation for the correlation between MRI and AR was seen, but in general the areas from 1 to 6 cm into the nasal cavity measured by AR were larger than areas measured by MRI, especially where the surface was most convoluted. The total volume for this region was 6.47 +/- 1.83 (SD) cm3 for AR and 5.65 +/- 1.34 cm3 for MRI. It was demonstrated that this could be due to errors in calculation of the areas on the basis of MRI and AR. In the posterior part of the nasal cavity and the epipharynx, there was a convincingly higher correlation between acoustic measurements and a scan perpendicular to the assumed geometrical axis of the epipharynx than between acoustic measurements and coronal scanning. This indicates that the sound axis roughly follows the geometrical axis. In a model of two tubes (nasal cavities) joined in a larger tube (the epipharynx), closure of the posterior part of the latter revealed that the contralateral nasal cavity is likely to cause overestimation of the posterior part of the epipharynx during AR compared with MRI.

Adult↗
PubMed1992

Angiotensin-converting enzyme inhibitor renography in the diagnosis of renovascular hypertension. Studies before and after angioplasty.

Renography with [99mTc] diethylenetriaminepenta-acetate (DTPA) was performed in 26 patients with renal artery stenosis (RAS), unilateral in 15 and bilateral in 11, and in 16 patients with essential hypertension with a normal renal angiogram. Nine of the patients with unilateral RAS were restudied after a successful percutaneous transluminal renal angioplasty (PTRA), i.e. complete removal of the stenosis and a normalization of the blood pressure without antihypertensive treatment. Single-kidney [99mTc]-DTPA clearance and parenchymal mean transit time (MTT) were determined at each examination. All patients were studied on two different days using the same procedure except that captopril 25 mg was given orally before renography at the second examination. In unilateral RAS captopril reduced single-kidney [99mTc]-DTPA clearance significantly on the affected side (-42.7%, median) but not on the unaffected side (-3.2%). In bilateral RAS single-kidney [99mTc]-DTPA clearance was reduced to the greatest extent on the most affected side (-43.0%) compared with the least affected side (-17.2%). In essential hypertension no significant changes were recorded on any side (-1.5% for both). After PTRA, single-kidney [99mTc]-DTPA clearance was not significantly changed by captopril either on the previously affected side (4.3%) or on the unaffected side. MTT was significantly prolonged after captopril on the affected side in unilateral RAS and on the most affected side in bilateral RAS, whereas no significant changes were found on the unaffected side in unilateral RAS, on the least affected side in bilateral RAS, or on any side in essential hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Ischemia in wound healing. I: Design of a flap model--changes in blood flow.

A standardized ischemic, H-shaped, double flap model in rats was developed for investigating the influence of different factors that could potentially increase flap survival. The blood flow was measured in the flaps as well as in normal healing incisional wounds on day -1 (intact skin) and on days 1, 4, 8, and 16 by the xenon-133 (133Xe) clearance technique. The flow in normal healing incisional wounds remained the same as the flow in intact skin. The flow in the flaps, however, initially decreased to ischemic levels, but afterwards gradually increased to that of normal healing incisional wounds and intact skin. Further, the cutaneous blood flow in both the cranially and the caudally based ischemic dorsal flap was independent of the width of the flap.

Animals↗
PubMed1991

Reliability of three computer methods in the analysis of ECG-gated radionuclide left ventriculography: interrecording, interobserver and intraobserver variability.

Three different computer methods for analysis of systolic and diastolic left ventricular function (ejection fraction, peak ejection rate, time to peak ejection rate, peak filling rate, time to peak filling rate, duration of fast filling phase, and fast filling fraction) as derived from ECG-gated radionuclide cardiography were compared in 30 patients with various diseases. The patients had two gamma camera recordings of the left ventricle performed immediately following one another during radionuclide (99mTc) equilibrium (3 x 10(6) counts, 16 frames/cycle, 64 x 64 pixels). Mean ECG R-R interval of the patients remained unchanged from first to second recording. The three computer methods were: (1) end-diastolic (ED) region of interest (ROI) analysis based on manually defined ED-ROI; (2) multi (M) ROI, manually defined ROI for each frame; and (3) semiautomatic (SA) ROI, ROI for each frame defined by an SA edge detection technique. With the 16 frame points as nodes, a 160-point time-activity curve was constructed for each of the three methods by use of a spline function. A tailored multiway analysis of variance showed that the M-ROI method had the highest interindividual range of values of the function parameters and the smallest interrecording, interobserver, and intraobserver variabilities. In theory this implies a better diagnostic sensitivity and specificity for the M-ROI method as compared with the other two methods.

Adult↗
PubMed1990

Calcium metabolism in postmenopausal osteoporosis: the influence of dietary calcium and net absorbed calcium.

A group of 85 females aged 48-77 years with postmenopausal crush fracture osteoporosis were investigated using a 7 day combined calcium balance and calcium tracer kinetic turnover study to assess the influence of dietary calcium and net absorbed calcium on bone metabolism. During the study, patients were on their habitual diet, as determined by a prestudy registration. Dietary calcium was measured after double serving of all the meals. All urine and feces were collected and analyzed for calcium content. Bone mineralization rate and bone resorption rate were determined by applying the continuously expanding calcium pool model to the tracer kinetic data. Urine calcium excretion and net absorbed calcium were correlated (r = 0.64, p less than 0.0001) with the following equation: urinary excreted calcium (mmol/day) = 2.4 + 0.4 X net absorbed calcium (mmol/day). Dermal calcium loss was not correlated with net absorbed calcium or urinary calcium. The net amount of absorbed calcium necessary to balance urinary and dermal losses was calculated to be 4.2 mmol calcium per day. The daily calcium intake necessary for obtaining a net absorbed calcium in excess of the urinary and dermal calcium losses and thereby ensure skeletal integrity was estimated to be 34.2 mmol calcium per day compared to an average intake of 27.9 +/- 7.6 (mean +/- SD) mmol/day. Net absorbed calcium correlated negatively to bone resorption rate (r = -0.31, p less than 0.005) and positively to bone mineralization rate (r = 0.29, p less than 0.01) and to calcium balance (r = 0.66, p less than 0.0001). Dietary calcium intake and calcium balance correlated positively (r = 0.38, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

The impact of unilateral ureteral obstruction on pelvic and parenchymal transit times in the pig kidney.

In 10 female pigs a partial unilateral ureteral obstruction was investigated for 3 weeks. The pigs were monitored with 131I-iodo-hippuran scintigraphies before obstruction and once a week during the course of obstruction. Parenchymal and pelvic mean transit times were calculated by deconvolution analysis. Before the pigs were killed, pelvic pressure and volume were measured. During the course of obstruction there was a slight, but significant (P less than or equal to 0.05) difference in renographical split function between the 2 sides. Parenchymal transit times increased moderately ipsilaterally during the 1st and 2nd week after obstruction and a significant difference (P less than 0.02) appeared in the 2nd week compared to the contralateral side, which was unchanged during the course of obstruction. Pelvic transit times increased steadily ipsilaterally during the course of obstruction and the opposite took place contralaterally. A fair correlation (r = 0.65) was found between parenchymal transit time and pelvic baseline pressure. Pelvic transit times were prolonged at any time after obstruction and significantly correlated to the presence of obstruction. The study suggests that interpretation of the obstructed renogram will encounter analysis of both parenchymal and pelvic transit times in cases where renal function is moderately reduced.

Animals↗
PubMed1990

Regional cerebral blood flow in pigs estimated by microspheres.

Regional cerebral blood flow in anaesthetized pigs is determined with the microsphere method. Five regions of cortical grey matter and three white subcortical areas in each hemisphere are examined together with anatomically classic structures. The validity of the biopsies was confirmed by freeze drying of the tissue. Three flow measurements in a group of six animals showed large interindividual variations whereas regions with the same structure in the particular animal showed a high degree of uniformity. Symmetrical regions in the two hemispheres were similar with a coefficient of variation between sides of less than 5%. The coefficient of variation of the particular flow measurements were 15%. The different brain structures have four discernible flow levels. White subcortical matter has three different flow values and forms together with medulla oblongata and hippocampus the low flow area. Flow in grey cortical matter is of the same magnitude as in unanaesthetized animals and constitutes together with thalamus, mesencephalon, pons and cerebellar hemispheres the intermediate flow level. The high flow areas are nucleus caudatus and lentiformis together with the cerebellar vermis. The choroid plexus, pituitary gland and pineal gland all have very high flow values and seem, in contrast to the rest of the brain, insensitive to the CO2-tension in arterial blood and global cerebral metabolism. Microsphere estimation of regional blood flow seems to be an appropriate technique for evaluating regional cerebral blood with a high degree of spatial resolution in repeated flow measurements.

Animals↗
PubMed1989

Differentiation between renovascular and essential hypertension by means of changes in single kidney 99mTc-DTPA clearance induced by angiotensin-converting enzyme inhibition.

Blood pressure (BP), plasma renin concentration (PRC), and 99mTc-labeled diethylenetriaminepenta acetate (DTPA) renography with determination of single kidney 99mTc-DTPA clearance and parenchymal mean transit time (MTT) were measured in exactly the same way on two consecutive days in 14 patients with renovascular hypertension (RVH), unilateral renal artery stenosis in nine and bilateral stenosis in five, and ten patients with essential hypertension (EH). The examination on day 1 served as a control for day 2 during which captopril (25 mg) was given orally one hour before measurements of PRC and DTPA clearance. Blood pressure was reduced by captopril in both groups, but the maximum decrease in systolic BP was slightly more pronounced (P less than .01) in RVH (22%, median) than EH (13%). Plasma renin concentration increased to a much greater extent (P less than .01) after captopril in RVH (366%) than in EH (46%), Single kidney 99mTc-DTPA clearance was significantly (P less than .01) reduced (-39.5%) and MTT considerably prolonged (170%) on the affected/most affected side in RVH, but both parameters were only slightly changed or unchanged on the unaffected/least affected side (-6.5%, -2% respectively) and were not significantly changed in any of the sides in EH. The degree of renal artery stenosis was significantly correlated to the increase in PRC (rho = -0.786, n = 14 patients, P less than .01), to the reduction in single kidney 99mTc-DTPA clearance (rho = 0.729, n = 19 kidneys, P less than .01) and to the prolongation in MTT (rho = -0.785, n = 16 kidneys, P less than .01). By analysis of the captopril-induced changes in 99mTc-DTPA clearance and MTT, it was possible to predict the existence of a moderate to several renal artery stenosis in arterial hypertension with a very high degree of probability, and the use of changes in 99mTc-DTPA clearance and MTT after angiotensin-converting enzyme (ACE) inhibition may become a valuable tool in differentiation between RVH and EH.

Adult↗
PubMed1989

Abnormal glomerular and tubular function during angiotensin converting enzyme inhibition in renovascular hypertension evaluated by the lithium clearance method.

Glomerular filtration rate (GFR) and tubular function were measured by means of the lithium clearance technique in 14 patients with renovascular hypertension (RVH) and eight patients with essential hypertension (EH) before and after oral administration of captopril 25 mg. In RVH captopril reduced 51-Cr-EDTA clearance (67.3 (median) to 47.5 ml min-1, P less than 0.01), proximal absolute reabsorption of fluid (53.9 to 41.5 ml min-1, P less than 0.01) and distal absolute reabsorption of sodium (2195 to 1402 mumol min-1, P less than 0.01), whereas proximal fractional reabsorption increased slightly (77.5 to 80.2%, P less than 0.02). In EH, however, these parameters were practically unaffected by captopril. In both RVH and EH plasma concentrations of angiotensin II and aldosterone were reduced after captopril, but atrial natriuretic peptide in plasma and urinary excretion rate of prostaglandin E2 were unchanged. Blood pressure decreased after captopril in both groups, but the maximum fall in systolic BP was more pronounced in RVH (22%) than EH (13%). It is concluded that angiotensin converting enzyme inhibition markedly reduced absolute reabsorption in both the proximal and distal tubules in RVH, in contrast to EH, predominantly due to fall in the GFR, and that the slight increase in proximal fractional reabsorption may be attributed to a reduction in the hydrostatic pressure in the peritubular vessels.

Adult↗
PubMed1989

Late cardiac deaths after isolated valve replacement for aortic stenosis. Relation to impaired left ventricular diastolic performance.

Sixty-three patients took part in a follow-up study ten to seventeen years after valve replacement for aortic stenosis. Data obtained were used to predict cardiac deaths (n = 14) occurring in the following three-year period. The degree of residual left ventricular (LV) hypertrophy correlated inversely with indices for LV systolic and diastolic performance (radionuclide cardiography). A logistic regression (LR) model had a positive predictive value for cardiac deaths of 100% (10/10) with 8% (4/53) false negatives. Evaluating LV performance indices exclusively, LR analysis showed that only peak filling rate had independent predictive value. Subnormal and normal LV ejection fractions were associated with equal three-year cardiac death rates (29%). Depressed LV function was related to residual hypertrophy. Impaired diastolic performance was the prime predictor of cardiac deaths.

Adult↗
PubMed1989

Reproducibility of iodine-123-hippuran renoscintigraphy in the normal pig at various flow rates.

Twenty-two pigs with normal kidney function and upper urinary tracts were examined with renoscintigraphies once a week for 4 weeks. In order to study the influence of urine flow on the reproducibility, renoscintigraphies were undertaken during various urinary flow rates. Renal split function was reproducible at any level of and independent of the urinary flow rates. For parenchymal and pelvic mean transit times a normogram was constructed for selected urinary flow intervals. An inverse relationship to urine production was seen. Parenchymal and pelvic transit times were fully reproducible when data were compared in two or three consecutive examinations of the same kidney at the same urinary flow rate. Both parenchymal and pelvic mean transit times were however significantly different (p less than 0.001) in kidneys studied from one urinary flow rate to another. Single kidney hippuran clearance was fully reproducible when compared in the same urinary flow interval. However a significant difference was found (p less than 0.05) when single kidney hippuran clearance was compared in renographies undertaken at different urinary flow intervals. Furthermore the study suggests that the size of hippuran clearance is dependent on the urine production, since an increase in hippuran clearance was seen in relation to increase in urinary flow. In conclusion this pig study showed, that monitoring of the urinary flow rate is extremely important in this very commonly used clinical investigation, and that the investigation should be performed in the same state of hydration at any renography to obtain reproducible results.

Animals↗