Nesting mallards (Anas platyrhynchos) forecast brood-stage food limitation when selecting habitat: experimental evidence.

By combining and reanalysing data from two independent field experiments we explore whether food limitation at the brood stage affects habitat selection in nesting mallards (Anas platyrhynchos). In an introduction experiment we found that, independent of treatment, some study lakes remained empty of wild mallard pairs ("empty lakes"), whereas on other lakes introduced birds attracted wild mallards ("attractive lakes"). In the other experiment we used mallard ducklings to address brood-stage food limitation by studying mass change of ducklings. We found that ducklings foraging on lakes that did not attract wild mallard pairs in the introduction experiment gained much less mass than those foraging on attractive lakes. In most cases ducklings even lost mass in the empty-lake foraging trials, providing strong evidence for food limitation. Therefore, lakes that remained empty of wild mallard pairs in the introduction experiment proved to be inferior brood habitats, particularly in terms of food. Our results give insight into the mechanisms underlying the general habitat selection hypotheses, specifically the ideal preemptive and conspecific attraction rules. The results further support our earlier conclusion that mallards do not use the ideal preemptive rule when selecting nesting lakes. However, conspecific attraction may not be generally applicable either, because, independent of the presence of introduced conspecifics, wild mallards somehow anticipated the low quality of the empty lakes as brood-rearing habitats and made their habitat-selection decision accordingly.

Suitability of cerebrospinal fluid as a signal-intensity reference on MRI: evaluation of signal-intensity variations in the lumbosacral dural sac.

The suitability of the cerebrospinal fluid (CSF) in the lumbosacral dural sac as an internal signal-intensity reference was studied on magnetic resonance imaging (MRI) of the lumbar spine using a surface coil and motion artefact suppression technique. A signal-intensity reference is needed when signal is compared between images, studies or subjects. Homogeneity of the CSF was estimated visually on T2-weighted images of 60 subjects at 1.5 T and of another 60 subjects at 0.1 T. Spines with a severely narrowed dural sac or marked scoliosis were excluded from the study to avoid partial volume effect. CSF was homogeneous in 82% and 73% of the examinations at 1.5 T and 0.1 T, respectively. The type and location of the local inhomogeneities did not relate to local narrowings of the dural sac. The signal intensity of CSF was measured in 108 examinations at 0.1 T after correcting the spatially-dependent signal-intensity non-uniformities with a phantom-based method. The signal-intensity difference between the CSF in the upper and lower lumbar dural sac was less than 10% in 73% of the examinations. The CSF in the lumbosacral dural sac can be a useful signal-intensity reference for estimation of the signal of the adjacent structures in patients without severe narrowing of the dural sac or marked scoliosis. It may contribute to assessing spinal disease processes.

Digital assessment of MRI for lumbar disc desiccation. A comparison of digital versus subjective assessments and digital intensity profiles versus discogram and macroanatomic findings.

During magnetic resonance imaging, a vast amount of digital data on anatomic structures is translated into images, which are then assessed subjectively. The development of an objective, sensitive method to directly assess the digital data would have clear benefits, particularly for clinical research on disc degeneration. The study goals were to develop a method of digital assessment of disc desiccation and to compare digital signal intensity profiles with discographic patterns and macroanatomic findings. Proton density-weighted MRIs were obtained from 45 males (9-77 years) and digital analysis was done with a freely selectable region of interest facility. The adjacent cerebrospinal fluid (CSF) was used as a reference for disc signal-intensity scores, and the disc to CSF-intensity ratio provided "adjusted digital scores." The CSF-adjusted digital method yielded reproducible scores that correlated with the subjective assessments. However, the CSF-adjusted digital scores were more sensitive than the subjective assessments, identifying findings that otherwise were undetected in younger subjects. Additionally, 10 cadaveric spines were evaluated using MRI with T2 and proton density-weighted sequences, discography, and macroanatomic dissection. MRI disc-intensity profiles were determined along a midsagittal line drawn through the disc. The profile of the digital scores along this line was then compared with discograms and macroanatomic sections. In all cases of disc degeneration on discograms, changes were present in the intensity profile. Based on both the living subjects and the cadaveric specimens, the digital assessments and disc intensity profiles appear to demonstrate disc degeneration, particularly in early stages.

Species composition of dabbling duck assemblages: ecomorphological patterns compared with null models.

Ecomorphological patterns of breeding dabbling duck (Anas spp.) assemblages were studied in six regions in northern Europe. Observed spacings among species in terms of bill lamellar density and body length were compared with expected spacings based on null models incorporating different levels of constraints (regional species pools, species relative abundances, lake size and habitat requirements of species). Deviations of observed spacings from expected ones were compared with prey abundance and prey size diversity in the lakes. Observed spacings in terms of body length, but not in terms of bill lamellar density, were greater than expected on the basis of null models. The most abundant species were generally relatively more different than less abundant species in terms of body length but not in terms of bill lamellar density. Deviations between observed and expected spacings in terms of body length were more like those predicted by the competition hypothesis in lakes with low food abundance than in lakes with high food abundance. Patterns in bill lamellar spacings were not related to food abundance nor to food size diversity. In general, patterns in body length spacings were consistent with the competition hypothesis whether the null model used in comparisons was constrained or not.

Is the signal intensity of cerebrospinal fluid constant? Intensity measurements with high and low field magnetic resonance imagers.

The signal intensity of cerebrospinal fluid (CSF) was studied by measuring the intensity of nine samples of CSF using various routine pulse sequences with 1.0 T and 0.1 T magnetic resonance imagers. The observed signal intensity differences between the CSF samples were small, as were the differences between the CSF samples and distilled water, although two of the samples were pathological with an elevated protein content. Signal intensity did not correlate with the protein content, and the location of the sample in the coil (head coils were used) caused more variation in the results than did the composition of the sample. The same results were obtained with both imagers. Our results suggest that CSF may be suitable for an intensity reference in routine patient studies in regions where the flow and pulsatile movement of CSF are slow enough not to affect the signal intensity, but further studies are needed to determine such regions in the CSF system.

Proton T1 relaxation time of normal and abnormal urine.

Relaxation times T1 of normal and abnormal urine samples were measured with a 0.02 tesla MRI device in a spectrometric mode. Protein containing urine from patients with glomerulonephritis showed a slight shortening of T1 relaxation time. Radiographic contrast medium, pH, osmolality or glucose in diabetes did not significantly change the T1 relaxation time of urine. Urine can be used as a T1 relaxation reference in MR imaging of the pelvis even if the patient has received radiographic contrast medium or has diabetes or proteinuria for any reason.

Effect of motion on the sonographic and magnetic resonance patterns of ageing blood.

The sonographic appearance of a hematoma may be affected by various factors, including the age of the hematoma. The effect of mechanical motion on the echogenicity and histologic appearance, and on the proton relaxation times T1 and T2 of blood clots, was studied in vitro for up to 21 days. All clots were of similar echogenicity and microscopic appearance during the first 2 days. The minimally disturbed clots were sonolucent from day 4 onwards, whereas moderate mechanical disturbance changed the microscopic structure of the blood clots and caused them to retain their echogenicity. Proton relaxation times T1 and T2 of both minimally disturbed and vigorously manipulated blood samples showed a rapid shortening of T1 and a less marked decrease of T2 between days 1 and 4, which was independent of mechanical motion. The ultrasonic appearance reflected the histologic appearance but not necessarily the age of the clot. The magnetic resonance (MR) parameters T1 and to a lesser extent T2 accurately reflected the age of the clot during the first 6 days. Although relatively gentle motion caused a large change in the ultrasonic appearance of the clots, vigorous shaking did not affect the magnetic resonance appearance of human blood clots.

Proton relaxation times in arterial wall and atheromatous lesions in man.

The proton relaxation times of autopsy samples of arterial intima-media were measured with an NMR spectrometer and results correlated to the microscopically estimated lipid content of the vascular wall. The normal arterial intima-media contained two T1 relaxation components. The short T1 component (T1s) was 90 +/- 13 ms and its relative weight was 11%. The long T1 component (T1l) was 523 +/- 89 ms and relative weight 88%, respectively. The average T2 was 99 +/- 18 ms. In diseased vessels, a positive correlation was found between the lipid content of the vessel wall and the relaxation rate of the fast component. T1s of the intima-media was significantly shorter (P less than .01) in severe atheromatosis compared with vessels without fat deposition. The results suggest that atheromatous lesions should be best highlighted in spin-echo images by using short TR and TE to suppress the influence of T1l and to avoid (noncontrast contributing) T2 decay of the signal intensity.

Effect of hemolysis and clotting on proton relaxation times of blood.

The proton relaxation times T1 and T2 of plasma and clotted blood stored in test tubes were studied at a magnetic field of 0.225 T as a function of time. A satisfactory description of both relaxation processes could be made by two exponential components for the plasma and three components for the clot. The major relaxation component in plasma was the slower one, the T1 of which shortened from about 1 300 ms to about 400 ms between the second and sixth day of storage. The plasma T2 behaved similarly, but shortened less. The shortening of the relaxation time in plasma surrounding the experimental thrombus was concluded to be due to a number of factors, including the release of hemoglobin into plasma, the conversion of hemoglobin to methemoglobin, a concomitant change in the configuration of hemoglobin molecules, and an increased concentration of iron in plasma. The shortening of the relaxation time may also occur in an in vivo hematoma and change the magnetic resonance appearance of a hematoma with time.

Conservative treatment of ureteric stones. Ureteric stones--surgical intervention.

The present report deals with 413 ureteric stone attacks treated in hospital and followed up to six years. If there was no need for emergency surgery, the patients were treated conservatively and followed with renograms on an out-patient basis after the initial evaluation. Stones up to 6 mm in diameter were passed during a reasonable time in 92% of the cases. In some cases an endoscopic procedure preceded the passage. Many of the larger stones were also passed. Nine of the 16 uretero lithotomies in the series were performed due to compromise in renal function during the follow-up period; these resulted in no permanent damage. Only two cases of slight renal damage occurred in the conservatively treated group of patients. There were no deaths or nephrectomies. The data suggest that modern follow-up facilities allow the safe adoption of very conservative attitudes in the treatment of ureteric stones.

Effective drainage of the bladder after transvesical prostatectomy.

The series presented consisted of 94 patients who underwent transvesical prostatectomy and whose bladders were drained by using a cystostomy tube (silastic) with an 8 mm lumen, in addition to a urethral catheter. Retention by blood clot was avoided. The wounds healed well, and no infection of the urinary tract occurred. The mean period of postoperative hospitalization was 9.5 days.

Vesico-ureteral reflux following transurethral slitting of the ureteral orifice.

A series of 14 patients treated with transurethral slitting of the ureteral orifice is presented. In 6 cases there was a stone at the distal end of the ureter and in 8 cases a ureterocele. Half the patients developed vesico-ureteral reflux. Other complications, such as urinary infection or renal scarring, have not been observed during the mean follow-up period of 47 months from the time of operation.

Instramedullary supramid pin and plate-screw fixation for fracture of the humerus.

A method of fixing the humerus is presented. A supramid pin is introduced into the medullary cavity and a plate with screws is attached to the bone surface. The screws are driven through the fracture fragments into the supramid pin. The resulting fixation is firm and suitable for certain complicated cases in which the usual fixation methods have their limitations.

Treatment of post-prostatectomy urinary incontinence with heterologous bone implant.

A description is given of an improvised method used in the treatment of post-prostatectomy urinary incontinence in a case in which a Kaufman 2 procedure had failed. At the second-operation, Kieler spongiosa bone packaged in a dacron net was used to support the bulbous urethra.