Search PubMed⌕ Search

Biomedical subjects

P Knoll

Publications and source records attributed to P Knoll.

At least 37 records · Page 2Linked to original sources
PubMed1999

An artificial neural net and error backpropagation to reconstruct single photon emission computerized tomography data.

At present, algorithms used in nuclear medicine to reconstruct single photon emission computerized tomography (SPECT) data are usually based on one of two principles: filtered backprojection and iterative methods. In this paper a different algorithm, applying an artificial neural network (multilayer perception) and error backpropagation as training method are used to reconstruct transaxial slices from SPECT data. The algorithm was implemented on an Elscint XPERT workstation (i486, 50 MHz), used as a routine digital image processing tool in our departments. Reconstruction time for a 64 x 64 matrix is approximately 45 s/transaxial slice. The algorithm has been validated by a mathematical model and tested on heart and Jaszczak phantoms. Phantom studies and very first clinical results ((111)In octreotide SPECT, 99mTc MDP bone SPECT) show in comparison with filtered backprojection an enhancement in image quality.

Algorithms↗
PubMed1999

Possible effect of calcitonin deficiency on bone mass after subtotal thyroidectomy.

Bone mass is purportedly reduced by an excess of endogenous or exogenous thyroid hormone or perhaps by calcitonin deficiency. Patients who have undergone thyroidectomy could be subject to all of these effects. In the present study we tried to demonstrate, whether lack of calcitonin following thyroidectomy has a significant influence on bone density. We measured thyroid hormone levels, TSH and calcitonin and assessed the bone mass in the hip and lumbar spine of 55 patients (32 f, 23 m), who had undergone a subtotal thyroidectomy between 1938 and 1996 on the reason of a non-toxic goitre. TSH levels were suppressed in 16 patients. Serum concentration of total calcium, intact PTH, osteocalcin were normal in all subjects. The mean fasting calcitonin level was in the patient group 2.09 +/- 0.7 pg/ml and in the control group, age matched healthy volunteers, 2.8 +/- 1.2 pg/ml. However, the serum level of calcitonin was not significantly lower than in the control group. 43 patients had an osteopenia or osteoporosis. The interpretation of the results in this study is hampered by the fact, that in women results may be influenced by involutional osteoporosis. Therefore we focus on the potential for osteoporosis among the 23 men. The results of our study indicates, that there is a significant reduction in bone mass in male after thyroidectomy, no matter whether T4 therapy is given or not, and whether TSH is suppressed or in a normal range.

Adult↗
PubMed1998

Bone scintigraphy in screening of torture survivors.

BACKGROUND: In most developed countries, survivors of physical torture inflicted for political, religious, or ethnic reasons face ever more stringent review when seeking asylum. In Austria, asylum seekers are required by immigration authorities to undergo medical examination as part of the review. Bone scintigraphy can detect bone lesions that are not detectable clinically or radiologically. We assessed the value of bone scintigraphy as corroboration of alleged injuries. METHODS: Human-rights organisations referred 25 asylum seekers to us from countries where torture is practised. We included patients who claimed to have been beaten by the security forces in their home country because of political or religious conviction or ethnic origin. Injuries had been inflicted 4 months to 5 years earlier. The patients (three women, 22 men) from 12 countries were categorised retrospectively into two groups: group A (n=12), tortured with blows from hard objects, and group B (n=13), tortured with blows from fists and kicks. We also used a control group of 25 individuals with the same age and sex distribution from the same countries who had no history of torture. FINDINGS: In group A, bone scans showed abnormalities in the area of alleged injury in all patients, whereas radiography was positive in only five patients. In group B, bone scans in the alleged areas of damage were positive in seven patients, but radiography yielded no positive outcomes. Among the controls there was one abnormal scan due to a known coxarthrosis. INTERPRETATION: Our preliminary results suggest that bone scintigraphy is a sensitive, non-invasive tool to document trauma some years after the actual injury.

Bone and Bones↗
PubMed1998

[The utility of various Doppler parameters at rest and during exercise for the diagnosis of residual stenosis after operation for aortic coarctation. A doppler-nuclear magnetic resonance comparison].

BACKGROUND: The postoperative follow-up of aortic coarctation (AoCo) is often characterized by persistent arterial hypertension, sometimes due to a residual narrowing at the site of surgical repair. A residual stenosis > or = 30% is considered to be significant. Anatomy of the aortic arch is best assessed by angiography, transesophageal echocardiography and magnetic resonance imaging (MRI). The use of these invasive and expensive procedures for routine examination in all patients who develop late systemic hypertension cannot be justified. Consequently, it would appear to be useful to find some noninvasive methods, such as Doppler gradients, that are capable of identifying any residual anatomic narrowing. OBJECTIVES: We compared different Doppler parameters obtained at rest and during exercise with the degree of narrowing at the site of surgical repair measured by MRI, in order to identify the indices predictive of residual stenosis. METHODS: Thirty-nine patients (26 M, 13 F) were studied after AoCo repair. Mean age was 21.7 +/- 9.7 years (9-49). Their age at the time of repair was 10 +/- 9.7 years (0.1-27) and the postoperative follow-up was 11.5 +/- 6 years (2-25). Systolic blood pressure measurement and Doppler echo for calculation of the transisthmic gradient at rest and during exercise on a bicycle ergometer were performed in all patients. The peak systolic gradient (PGs) over the isthmus was calculated using the simplified Bernoulli equation: PGs = 4 x (V2(2)-V1(2)), where V1 and V2 are the peak velocities in the ascending and descending aorta. In addition, at the end of exercise the peak diastolic gradient (PGd) was measured at the end of the T wave on the ECG, and the systolic velocity half-time (SVHT), as the time interval from the peak to the half peak systolic velocity. MRI of the aorta was performed to measure the diameter of the isthmus (AI) and of the descending aorta at the diaphragm (DA). Residual narrowing at the isthmus was expressed as stenosis % = [(1-(AI/DA)]%. RESULTS: At rest: systolic blood pressure 128.3 +/- 22.5 mmHg, PGs 15.9 +/- 8.1 mmHg (1-32). None of the patients had PGd. At peak exercise: systolic blood pressure 207 +/- 37 (160-265) mmHg, PGs 32.3 +/- 14.7 mmHg (8-70), SVHT 96 +/- 23 msec (60-139) and PGd 7.2 +/- 4.8 mmHg (1-17). Stenosis % measured by MRI was 23.1 +/- 14.5% (0-53) and in particular, it was < 30% in 25 patients and > or = 30% in 14 patients. Both the PGs at rest and the other Doppler parameters at peak exercise (PGs, SVHT, PGd) correlated with stenosis %. SVHT together with PGd on exercise Doppler represented the combination of two variables that was best for predicting a residual stenosis. When all three variables obtained by exercise Doppler were combined, every patient with residual stenosis was correctly identified. In particular, the combination (PGs > or = 28 mmHg + SVHT > or = 108 msec + PGd > or = 8 mmHg) identifies all patients with stenosis > or = 30%, while the combination (PGs < or = 38 mmHg + SVHT < 108 msec + PGd < 10 mmHg) excluded those with significant stenosis. CONCLUSION: Parameters obtained from the transisthmic gradient (PGs, SVHT, PGd) measured at peak exercise by CW-Doppler can diagnose a residual stenosis % in operated AoCo. We propose using this noninvasive method of identifying patients who need to be referred for MRI.

Adolescent↗
PubMed1998

Decisive diagnosis of seronegative polyarthritis by 3-phase bone scintigraphy.

Inflammatory joint disease is mainly diagnosed on grounds of clinical investigation, laboratory testing (acute phase reactants), and radiography. Radionuclide imaging has recently been added to the armamentarium of clinician. This case report points out the role of three-phase bone scan and HIG (human immunoglobulin) scan in the discovery of the inflammatory nature of polyarthralgia in a young woman with equivocal clinical and laboratory results. In the aim of diagnosing arthritis early in its course scintigraphy proved to be superior to conventional radiography. It also allows more discriminating selection of subsequent X-ray examination to limit radiation exposure.

Acute-Phase Proteins↗
PubMed1996

[Corrected transposition of the great arteries in geriatric age. Report of a case diagnosed by magnetic resonance imaging].

Corrected transposition of the great arteries (cTGA) is a rare condition, and few patients with this abnormality survive the 50th year of age because of associated anomalies or the subsequent development of left atrioventricular valve regurgitation or heart block or both. We report the case of a 75 years old man with cTGA without associated anomalies which seems to be of particular interest because of the following reasons: 1) cTGA is a rare condition in advanced age; 2) the diagnosis has been made by MRI which allowed a complete segmental analysis; 3) this case confirms that the morphologic right ventricle in systemic position can function appropriately over a long term. We conclude that MRI can be an alternative to Echocardiography in patients with complex congenital cardiac disease who exhibit a poor ultrasound window.

Aged↗
PubMed1994

[The value of nuclear magnetic resonance tomography in evaluating the patency of aortocoronary bypass grafts].

BACKGROUND: Patients with previous coronary artery bypass graft surgery often present with pain of unknown origin. Noninvasive documentation of graft patency is of obvious clinical importance. METHODS: In order to assess the efficacy of magnetic resonance imaging (MRI) in evaluating graft patency, 44 patient with prior coronary artery bypass graft surgery and a history of chest pain were studied by coronarography and MRI. MRI was performed within 2.1 +/- 3.8 days from coronarography using a 0.5 Tesla magnet, Spin-Echo T1 technique, cardiac and respiratory gating and scannings in transaxial plans. A graft was defined as patent, if a signal void was identified in at least two different slices in a position consistent with a bypass graft. Images were analyzed by two different observers aware of the type of surgery but not the result of the coronarography. RESULTS: Eighty-nine out of 100 grafts were classified correctly by MRI. Sixty-three grafts were patent as shown by coronarography; 59 of them were classified correctly by MRI. Thirty-seven grafts were shown as occluded; 30 of them were classified correctly by MRI. In particular, 43 out of 45 grafts to the left anterior descending artery, 18 of them using the internal mammary artery, 23 out of 30 graft to the left circumflex artery and 23 out 25 grafts to the right coronary artery were classified correctly. CONCLUSIONS: This study demonstrates the capability of MRI to evaluate coronary artery bypass graft patency with a sensitivity of 94% and specificity of 81%; this technique has significantly clinical limitations because resolution is not adequate to evaluate the presence of graft stenosis.

Adult↗
PubMed1993

Late results following proximal reinsertion of isolated ruptured ACL ligaments.

Between 1982 and 1984, 49 patients with fresh isolated proximal ruptures of the anterior cruciate ligament (ACL) were operated on in the Trauma Hospital, Salzburg. The operation was performed within 1 week of trauma. The operational technique used was proximal reinsertion of the ruptured ACL alone. Postoperatively the knee was immobilized for 6 weeks in an above-the-knee plaster cast. We were able to re-examine 42 of the 49 patients 5-7 years after injury. In addition to a clinical examination, testing with a KT-1000 arthrometer was performed. The objective and subjective results we found were evaluated using the Lsyholm score and OAK knee evaluation form. We found 12 (29%) absolutely stable knee joints. We accepted a KT-1000 result of up to 3 mm as satisfactory, and 81% of our patients were in this category. The same percentage (81%) scored between 85 and 100 points on the Lysholm scale. Only 52% scored over 90 points on the OAK form. Subjectively only 6 patients (14%) were dissatisfied with their result.

Adult↗
PubMed1993

[Long-term follow-up in patients operated on for aortic coarctation. The echo-Doppler and MRI assessment of left ventricular function and the transisthmic gradient].

BACKGROUND: Hyperdynamic left ventricular function and increased left ventricular mass has been recently reported in the long-term follow-up of patients after successful repair of aortic coarctation (AoCo). METHODS: We studied 35 patients, mean age 22.7 years (range 1-47), following repair of AoCo in order to evaluate: 1) left ventricular mass and systolic function by M-mode echocardiography in comparison with 20 healthy control subjects; 2) the prevalence of systemic hypertension; 3) systolic blood pressure and the trans-isthmic gradient by CW Doppler at rest and after exercise; 4) subjects with a hypertensive response and/or with a significant trans-isthmic gradient during exercise, correlating such parameters with indexes of left ventricular function and the ratio of aortic isthmus/aortic diaphragmatic diameters (AOI/AOD) by means of Magnetic Resonance (MR). At the time of operation, mean age was 12.4 years (range 1 mo-40 yrs) and the follow-up period was 10.1 years (range 6 mo-26 yrs). RESULTS: Left ventricular mass index (Mi) was significantly greater in comparison with that of the controls (96.5 +/- 25 vs 71.5 +/- 16.6 g/m2; p < 0.001); the mean velocity of circumferential shortening (mVCFc) was increased (1.4 +/- 0.25 vs 1.2 +/- 0.16 circ/s; p < 0.005); the end systolic meridional stress (ESS) was decreased (37.3 +/- 11.1 vs 47.9 +/- 13.1 g/cm2; p < 0.005) while the peak systolic meridional stress (PSS) was not significantly different in the two groups. Fourteen out of 35 patients (40%) showed an exaggerated mVCFc for the level of ESS, which indicates an increased inotropic state. Hypertension at rest was present in 10 patients (28%). Mean age at the time of operation of the hypertensive group was higher than that of the normotensive one (21.4 +/- 10 vs 8.9 +/- 8.6 yrs; p < 0.001). All patients showed a small systolic gradient across the side of coarctation repair at rest (mean 13.1 mmHg; range 0-30). The exercise test was stopped in 5 patients because of hypertension (> 250 mmHg); 24 patients (80%) showed an exercise-induced hypertension. The mean gradient at maximal exercise was 25.9 mmHg (range 0-52); 6 patients (20%) developed a diastolic gradient. With MR it was possible to evaluate the anatomy of the aortic arch and the descending aorta in all cases. The mean ratio AOI/AOD was 0.81 (range 0.63-1). The age at the time of operation showed a positive correlation with the systolic blood pressure (r = 0.63; p < 0.001) and with Mi (r = 0.45; p < 0.005). The systolic blood pressure and the gradient at maximal exercise also showed a positive correlation (r = 0.40; p < 0.01). CONCLUSIONS: In the long-term follow-up of patients after successful coarctation repair there are persistent alterations of left ventricular function with hypertrophy, hyperkinesia and increased inotropic state. Hypertension at rest and after exercise could persist despite good surgical results.

Adolescent↗
PubMed1993

[Magnetic resonance with the spin-echo technic in the noninvasive evaluation of the patency of aortocoronary bypasses: preliminary data].

BACKGROUND: Patients with previous coronary artery bypass graft surgery often develop chest pain due to ischemic or nonischemic causes. Noninvasive evaluation of graft patency is thus of obvious potential importance. METHODS: In order to assess the efficacy of magnetic resonance imaging (MRI) in evaluating graft patency after coronary artery bypass graft surgery, 16 patients with prior surgery and history of chest pain were studied prospectively by coronarography and MRI. These 16 patients with a total of 40 grafts were evaluated, using MRI with Spin-Echo T1 technique within 3.6 +/- 4.4 days from coronarography with a 0.5 Tesla magnet, cardiac and respiratory gating and scannings in transaxial planes. A graft was defined as patent if a signal void was identified in at least two different slices in a position consistent with a bypass graft. Images were analyzed by two different observers aware of the type of surgery but not the result of the coronarography. RESULTS: Thirty-six out of the 40 grafts were classified correctly by MRI. Twenty-eight grafts were patent as shown by coronarography; 26 of them were classified correctly by MRI. Twelve grafts were shown as occluded; 10 of them were classified correctly by MRI. In particular, all of the 14 grafts to the left anterior descending artery (3 of them using the internal mammary artery), 13/16 of the grafts to the left circumflex artery and 9/10 of the grafts to the right coronary artery were classified correctly. CONCLUSIONS: This study demonstrates the capability of MRI to evaluate coronary artery bypass graft patency with a sensitivity of 92.8% and specificity of 83.3%; this technique has significant clinical limitations because resolution is not adequate to evaluate the presence of graft stenosis.

Adult↗
PubMed1989

[Diagnosis and treatment of carotid artery stenoses].

20 to 30% of all strokes are caused by stenosing processes of the extracranial part of the carotids. The frequency and severity of cerebrovascular disease can be reduced by early diagnosis and treatment. Ultrasonography consisting of Doppler flow analysis and B-mode imaging sonography is an excellent diagnostic procedure for screening patients with suspected cerebrovascular disease so that morbidity and mortality are supposed to be lowered in future. This survey will briefly review different types of surgical and pharmacological therapy in the context of primary and secondary prevention of stroke.

Brain Ischemia↗
PubMed1989

[Quantitative evaluation of left ventricular systolic function using bidimensional echocardiography: comparison with cineangiography].

The aim of the study was to compare the evaluation of the left ventricular systolic function performed both by angiography and 2D-echocardiography on 80 subjects (31 with coronary artery disease, 18 with left ventricular volume overload, 10 with left ventricular pressure overload, 14 with mitral valve disease and 7 normal controls). The 2D-echocardiograms of the left ventricle with simultaneous measurement of the right arm systolic blood pressure was performed within 24 hours of the angiographic examination. The following parameters were obtained using the two methods: end-diastolic volume index, end-systolic volume index, ejection fraction, left ventricular mass index, mass/volume ratio, end-systolic circumferential stress, contractility expressed as end-systolic circumferential stress/end-systolic volume ratio; the end-systolic circumferential stress/ejection fraction ratio was calculated only by 2D-echocardiography. The afterload and contractility were not calculated in subjects with coronary artery disease and left ventricular outflow gradient. No statistically significant differences were shown between the two methods, except a slight under-estimation by echocardiography of the angiographic end-diastolic volume index (93.1 +/- 38.9 ml/m2 vs 115 +/- 39.9 ml/m2; p less than 0.01) and over-estimation of the mass/volume ratio (1.38 +/- 0.33 g/ml vs 1.2 +/- 0.44 g/ml; p less than 0.01) was shown between the two methods for all parameters. A depressed contractile state was also demonstrated by the end-systolic circumferential stress/ejection fraction ratio. The inter and intraobserver variability was 6.6 +/- 4.4% (range 0.16%) and 4.2 +/- 3% (range 1.11%) respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗