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Biomedical subjects

P Landwehr

Publications and source records attributed to P Landwehr.

At least 73 records · Page 4Linked to original sources
PubMed1991

Quantification of vascular stenosis with color Doppler flow imaging: in vitro investigations.

The accuracy of quantifying the degree of vascular stenosis with color Doppler flow imaging (7.5-MHz, linear array system) was determined in an experimental study carried out on six concentric and five eccentric model stenoses (cross-sectional area reduction, 13.4%-93.8%). The measurements were made with use of pulsatile flow at four different flow rates (70.8-339.0 mL/min). The degree of stenosis was calculated from the ratio of prestenotic to intrastenotic flow velocity. The most exact measurement of the degree of stenosis could be achieved with Doppler spectral analysis by determining the maximum peak systolic velocity (r = .994, y = 0.98x - 3.2). With the velocity values derived only from the color-coded image, it was also possible to find the most exact degree of stenosis (r = .995, y = 0.99x - 2.9). For quantification of stenosis, pre- and intrastenotic Doppler spectral analysis is no longer necessary if the stenosis can be imaged sufficiently with color Doppler.

Blood Flow Velocity↗
PubMed1991

[4 years' experience with a balloon-expandable endoprosthesis. Experimental and clinical application].

During a 4-year period of clinical application of the balloon-expandable Palmaz stent, a randomized trial comparing stent implantation and traditional balloon angioplasty of iliac arteries in arterial occlusive disease was started. The first long-term results, recorded after 2 years, indicate statistically significant differences in the complication rate (after stenting 2/62 and after angioplasty 5/69) and patency (greater than or equal to 70% of original lumen size upon stent implantation or balloon inflation: 95% after stenting and 72% after angioplasty). Clinical improvement after 2 years was 89% after stenting and 70% after angioplasty. Parallel to the clinical trials, experimental canine artery stenting was performed to evaluate differences in the long-term patency of stents exposed to restricted flow. Significant differences in neointimal healing were found between normally perfused stents and stents with artificially reduced flow: during the total observation period of 6 months the neointimal height was up to 200% higher in flow-restricted stents, while the histological composition of the neointima was the same as with normally perfused stents.

Angioplasty, Balloon↗
PubMed1991

[A ROC analysis for comparing contrast perception in grey scale reversal of digital images].

Based on ROC (receiver operating characteristic) analysis, contrast perception by eight physicians engaged in x-ray diagnostics for different lengths of time was examined in respect of inversion of grey scale values of digital x-ray film images. The ROC analysis showed a significantly superior contrast perception for imaging by the negative mode (bones white) than by the positive mode (bones black). With r* = + 0.61 a positive correlation was obtained between the period of the physicians' activity in x-ray diagnostics and the difference between the areas below the ROC curves for both imaging modes. Hence, the negative mode is to be preferred for diagnostic work based on digital x-ray film images.

Humans↗
PubMed1991

[Clinical value of sialography in digital and conventional imaging technique].

Digital subtraction sialography offers a new technique for the diagnosis of salivary gland disease. The basis of this technique is the removal of superimposed bony structures. Ninety-one patients (4-77 years old) with acute and chronic inflammatory disorders, chronic sialectasis, chronic sialolithiasis and tumours of various types underwent sialography using the digital subtraction technique. In addition, conventional sialography using a 100 mm camera and high resolution ultrasonography was performed. The results were compared with the histopathology and intraoperative findings. The digital subtraction technique is superior in recognition of inflammatory changes and chronic sialolithiasis, whereas ultrasonography is more sensitive in diagnosis and localization of tumours.

Adolescent↗
PubMed1990

Collateral pathways in portal hypertension.

In a retrospective study angiographic image material of percutaneous direct portographies carried out in 43 patients was evaluated according to anatomic and radiologic criteria. These examinations were performed for therapeutic purposes (embolisation of vessels supplying varices). All the hepatofugally perfused veins were analyzed according to their localisation and course. Apart from the known portocaval collateral pathways a number of other collaterals not yet described could be documented by means of angiography.

Aged↗
PubMed1990

[Diagnosis of acute deep leg vein thrombosis with compression ultrasonography].

We studied the accuracy of compression sonography in 238 patients suspected of deep venous thrombosis comparable to phlebography. The veins in the thigh were considered to be occluded when their lumen did not collapse under slight pressure with the scanner. In the lower leg, incompressible echosparse strings were regarded to be equivalent to thrombosed veins. Since in some patients both legs were submitted to phlebography, 301 x-ray-examinations of one leg were compared to ultrasound. 153 thromboses were detected by venography. Ultrasound diagnosis of venous occlusion was made with a sensitivity of 96% and a specificity of 99%. In 91% it was possible to predict the extent of the clot. Thigh vein thromboses were correctly seen with a sensitivity of 97% and a specificity of 99%. Isolated calf vein thromboses were detected with a sensitivity of 90% and a specificity of 99%. In 10% of the examinations ultrasound brought new essential information compared to phlebography. We conclude that compression sonography is an accurate method in the diagnosis of deep venous thrombosis and that it should be applied liberally in patients with suspected venous occlusions.

Diagnosis, Differential↗
PubMed1990

[The value of color-coded duplex sonography of a dialysis shunt].

Two hundred and sixty-four shunt segments in 43 patients with 66 dialysis shunts were examined by colour-coded duplex sonography and the results compared with DSA. Sonography demonstrated shunt stenoses with an accuracy of 93.9% (sensitivity 90.6%, specificity 95.8%). Only central venous stenoses were shown better by DSA than by sonography. Sonography showed occlusions with a sensitivity of 83.3% and a specificity of 100%. All aneurysms demonstrated by DSA were correctly identified by sonography. In 18 patients PTA of the shunt was performed. The result of treatment could be quantified by measuring flow by means of sonography. The study confirmed the value of duplex sonography as a noninvasive diagnostic method for investigating insufficient dialysis shunts.

Adult↗
PubMed1990

[Dilatation and balloon-expandable stents for the treatment of central venous stenosis in dialysis patients].

On 10 dialysis patients we performed 12 balloon dilatations, 2 catheter lyses, 6 stent implants (Palmaz stent) and one atherectomy of central venous stenoses or occlusions (v. subclavia, v. brachiocephalica) at the shunt arm of the patient. The primary success rate was, in balloon PTA and lysis, 12/14 interventions, and in stent placement and atherectomy 7/7. The angiographical and clinical primary result after stent implantation was significantly better than after conventional dilatation. After 66% of the balloon dilatations recidivation occurred within the first year; this can be treated by means of repeated PTA. Whether long-term exclusion of recurrence can be achieved by stent implantation, must be established by means of follow-up studies that are at present in progress.

Adult↗
PubMed1990

[Color-coded duplex sonography before and after PTA of the arteries of the lower extremities].

The value of color-coded duplex sonography in the pelvic and lower limb arteries was studied prospectively in 52 patients and the findings were compared with intra-arterial DSA. There was high diagnostic accuracy (sensitivity 91.7%, specificity 98.9%) for the demonstration of vascular abnormalities. In 84.3% of cases a correct diagnosis could be obtained based entirely, or largely, on the color-coded signal. Both before and after PTA color-coded duplex sonography is a non-invasive method that is superior to conventional duplex sonography.

Angiography, Digital Subtraction↗
PubMed1990

[Magnetic resonance tomography (MRT) of the hand in chronic polyarthritis].

Forty hands of 39 patients with rheumatic joint disease were examined by MRT. The method differentiates between inflammatory exudative and proliferative processes in soft tissues and bone. T2-weighted images provided criteria for judging the activity of the disease. MRT provided better demonstration of the soft tissues than just conventional radiography. The methods were of equal value for showing bone lesions. MRT is suitable as a means of diagnosing rheumatoid changes in the hand.

Adult↗
PubMed1989

[Imaging properties of digital image-intensifier radiography compared to the conventional x-ray technic for chest pictures].

Projection properties of a digital fluorographic system for chest examinations are examined using varying test phantoms. A maximal geometric distortion of +14% between the centre and the periphery of the image intensifier and a maximal spatial resolution of 2.6 LP/mm is found. Contrast detail diagrams are used to show the combination of spatial and contrast resolution of the system. Compared with diagrams for conventional radiographic systems there is a significant loss of resolution.

Adolescent↗
PubMed1989

[In vitro measurement of intravascular blood flow with color Doppler sonography].

The accuracy of colour Doppler sonography for measuring various aspects of intravascular flow (volume and velocity), under varying conditions, was studied experimentally. The effect of variable Doppler angles, different flow paths, frequency and vessel diameter on flow profiles was examined. At all levels of measurement (range 14 ml/min to 566 ml/min) there was a very close correlation between the actual and measured values (r greater than 0.99) and high accuracy. In the detection of very slow flow rates, the use of a specific high pass filter technique was able to quantify blood flow velocities of just under 1 cm./second. Multigated colour Doppler sonography is better for measuring flow volumes than a single channel duplex system.

Blood Flow Velocity↗
PubMed1989

[Digital image intensifier radiography and film-screen combinations in pulmonary nodules].

30 patients with known or suspected pulmonary nodules were examined using a digital image intensifier radiography system, a conventional radiography system and a tomography of the whole lung. 73.8% of the pulmonary nodules detected with tomography were also detected with the digital system, 69.1% with the conventional system. There was no significant difference between the two systems comparing false positive and false negative diagnoses. Regarding the dose reduction to nearly 25% of that of a conventional examination the digital technique should be preferred to the conventional technique, if pulmonary nodules are suspected.

Humans↗
PubMed1989

[Effect of magnetic resonance tomography on therapy planning in incontinence after anal atresia].

Five healthy children and 16 children, ages 6-17 years, who had been operated on for anorectal atresia underwent magnetic resonance (MR) imaging of the pelvis. The development of sphincter muscles and the location of the pulled-through intestine in relation to the sphincter muscles were evaluated by a muscle score. There was good correlation between MR muscle score and clinical continence score. MR imaging provides additional information for therapeutic management and surgical procedures to improve continence.

Adolescent↗