Pneumothorax resulting from subclavian puncture: a complication of permanent pacemaker lead implantation.

Pneumothorax is a mild complication during pacemaker lead implantation using the subclavian puncture technique. We report on five-year experience in 433 pacemaker lead implantation procedures in 379 patients. The cephalic vein route was solely used in twelve patients. Three procedures were performed over time in four patients and one patient needed four repetitive punctures for pacemaker lead implantation and replacement. Thus 421 punctures were carried out in 367 patients. Eleven case of pneumothorax were observed: in eight patients (1.9%) a partial pneumothorax occurred and in three patients (0.7%) the pneumothorax was nearly complete. In the latter patients a chest tube was inserted and hospital admission was prolonged for 3, 6 and 6 days, respectively. Old age with a corresponding abnormality in the form of chest deformation were predominantly found in the patients with this type of complication.

Evaluation of two cortical fraction estimation algorithms for the calculation of dynamic magnetic resonance renograms.

With the high resolution of dynamic magnetic resonance imaging (MRI) scans it is possible to measure cortical renograms directly, but due to partial volume effects this is impossible for medullary renograms. With weighted subtraction of the cortical renogram from a mixed renogram it becomes possible to extract the medullary renogram. For this subtraction the fraction of cortical tissue, present in the region of interest in which the mixed renogram is determined, has to be calculated. We have evaluated two algorithms for calculation of the cortical fraction. Both algorithms use the fact that during an interval after the start of the cortical enhancement no medullary enhancement occurs. One algorithm calculates the ratio between the slopes of both enhancement curves. The other is based on minimising the medullary signal values using a least squares error (LSE) method. Using a computer model of the renograms and measurements on real patients we analysed the accuracy of both methods and determined the best parameters for each.

Movement correction of the kidney in dynamic MRI scans using FFT phase difference movement detection.

To measure cortical and medullary MR renograms, regions of interest (ROIs) are placed on the kidney in images acquired using dynamic MRI. Since native kidneys move with breathing, and breath-holding techniques are not feasible, movement correction is necessary. In this contribution we compare three correction methods, based on image matching, phase difference movement detection (PDMD), and cross-correlation, respectively. The PDMD-based method showed the best performance and was able to determine kidney movement in our test series in 68% of the scans with no visible deviation, and in 88% of the scans if a one-pixel deviation is considered acceptable.

MR renography by semiautomated image analysis: performance in renal transplant recipients.

We evaluated a method of semiautomated analysis of dynamic MR image series in renal transplants. Nine patients were studied twice, with an average time interval of 7 days. MR examination consisted of a run of 256 T1-weighted coronal scans (GE; TR/TE/flip: = 11/3.4/60 degrees; slice thickness = 6 mm; temporal resolution = 2 seconds). Gadolinium-DTPA (0.05 mmol/kg) was injected with an injector pump (5 ml/seconds). MR renographs of the cortex and medulla were obtained by segmentation of the renal transplant and placement of two regions of interest (ROIs) overlying the peripheral and central renal parenchyma. In the first 100 frames of the renographs, analysis of variance (ANOVA) demonstrated significant intraclass correlation coefficients with mean values for the cortex and medulla of 0.47 and 0.59, respectively. We conclude that the procedure is a robust technique that generates meaningful signal curves.

MR renography: an algorithm for calculation and correction of cortical volume averaging in medullary renographs.

We evaluated a mathematical algorithm for the generation of medullary signal from raw dynamic magnetic resonance (MR) data. Five healthy volunteers were studied. MR examination consisted of a run of 100 T1-weighted coronal scans (gradient echo; TR/TE 11/3.4 msec, flip angle 60 degrees; slice thickness 6 mm; temporal resolution 2 seconds). Gadolinium-diethylene triamine pentaacetic acid (DTPA; 0. 05 mmol/kg) was injected with an injector pump (5 ml/sec). Medullary MR renographs (MRRs) were calculated for regions of interest with strong and moderate cortical volume averaging (CVA). A reference medullary MRR, devoid of CVA, was obtained. Percentual signal differences between calculated and reference medullary MRRs were estimated for each consecutive scan. Run averaged values of these differences were calculated. Mean values, after subtraction of the resting state signal, were +0.2% (SD 9.7%) and +0.7% (SD 9.0%) for areas with strong and moderate CVA, respectively. We conclude that with this algorithm reliable extraction of medullary MRRs is feasible, providing a unique tool for clinical evaluation of medullary disease. J. Magn. Reson. Imaging 2000;12:453-459.

Reduction of noise in medullary renograms from dynamic MR images.

Dynamic magnetic resonance images of the kidney can be used to acquire separate renograms of the cortex and medulla. A high-quality cortical renogram can be determined directly from a region of interest (ROI) placed in the cortex. Due to partial volume effects, part of the signal from a ROI placed in the medulla is caused by cortical tissue. By subtracting a fraction of the cortical signal from the cortico-medullary signal, a purer medullary renogram can be obtained. A side effect of this subtraction is an increase in noise level. The noise level increases with larger partial volume fractions. Using a matched image filter, it is possible to exclude those areas from the ROI that have a high partial volume content, thus reducing the amount of cortical signal that has to be separated from the medullary signal. Noise reductions of up to 50% have been achieved in the medullary renogram, with an average reduction of 23%.

New MRI findings in Creutzfeldt-Jakob disease: high signal in the globus pallidus on T1-weighted images.

We report a 49-year-old woman with Creutzfeldt-Jakob disease (CJD). In addition to typical high-signal lesions on proton-density and T2-weighted images there was high signal in the globus pallidus bilaterally on T1-weighted images. The latter feature has not been described previously and probably due to deposition of prion protein, as found at autopsy.

Congenitally short trachea with compression of the left mainstem bronchus: MRI findings.

The MRI features of congenitally short trachea in a patient presenting with respiratory distress are presented. Compression of the left mainstem bronchus by the aortic arch, a recognised complication of this anomaly, could be demonstrated by MRI, obviating the need for other imaging modalities.

Effect of ephedrine on muscle weakness in a model of myasthenia gravis in rats.

In addition to therapy with anticholinesterases, ephedrine is sometimes used to improve muscle strength in myasthenia gravis, with variable results. The efficacy of ephedrine was tested in rats with a alpha-bungarotoxin-induced model of myasthenia gravis. The rats showed a drooping lower lip and impaired capability of drinking. Injections of neostigmine caused an improvement of the position of the lip. Ephedrine caused some improvement. However, ephedrine had no effect, either on the lower lip or on water consumption, when the sleep-wake cycle was reversed and the rats had their active period during day time. It was concluded that the effect of ephedrine was unspecific and probably due to arousal from drowsiness. The results suggest, therefore, that the variability of the effect of ephedrine in myasthenic patients is unrelated to neuromuscular transmission per se but rather due to a difference in susceptibility to arousal.