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K F Kreitner

Publications and source records attributed to K F Kreitner.

At least 37 records · Page 2Linked to original sources
PubMed2000

[Flow quantification in coronary and bypass vessels with MR phase contrast technique].

PURPOSE: To evaluate accuracy of velocity encoded cine MR imaging for determination of blood flow in coronary arteries and coronary bypass grafts. MATERIALS AND METHODS: 12 patients with 22 coronary bypass grafts underwent intraoperative flow quantification using the transit time ultrasound method. These values were compared to postoperative MR phase shift measurements. Flow measurements were performed preoperatively in 28 coronary arteries of 20 patients. For flow measurement, we used a velocity-encoded k-space segmented gradient echo sequence with a temporal resolution of 110 or 125 ms, respectively. 6-8 pase shift images could be acquired during one cardiac cycle. RESULTS: There was a significant correlation between intraoperative and flow measurements using velocity-encoded MR imaging (r = 0.74, p < 0.0001, t-test). Flow volumes determined by MR imaging were systematically larger than those determined by the transit time ultrasound method. Mean flow in coronary arteries was reduced in severely stenosed vessels (> 70%) compared to normal vessels. Intra- and interobserver variability were 10.5 and 15% (coronary bypass grafts), and 12.3 and 15.8% (coronary arteries), respectively. CONCLUSIONS: Velocity-encoded MR imaging enables determination of flow in coronary artery bypass grafts and coronary arteries. Future developments should aim at the improvement of spatial and temporal resolution of the method.

Adult↗
PubMed2000

MR arthrography of the shoulder: comparison of low-field (0.2 T) vs high-field (1.5 T) imaging.

The objective of this study was to compare the image quality, sensitivity, specificity, and diagnostic accuracy of an open low-field MR system (0.2 T) with a standard high-field MR system (1.5 T) after arthrography of the shoulder. Thirty-eight patients either with suspected chronic instability (n = 12) or rotator cuff abnormalities (n = 26) were examined. Intra-articular injection of diluted Gd-DTPA was followed in randomized order either first by imaging on an open 0.2-T system or on a 1.5-T system. The image material was evaluated independently by two radiologists in a blinded fashion with respect to overall image quality and the detection of rotator cuff as well as capsular and labral abnormalities. Surgical correlation was available in 27 (71%) of 38 patients. For both systems, sensitivity and specificity for rotator cuff tears were 100% each, and for labrum pathologies, these values were 100 and 93%, respectively. The agreement for detection of labral pathologies between low-field and high-field examinations was good (kappa = 0.69, kappa = 0.61). For the detection of full-thickness tears of the rotator cuff, the agreement between the low-field and high-field MR examinations was very good and significant (kappa = 0.94, kappa = 1, p < 0.001). Overall image quality was rated good in 17 (45%) and fair in 21 (55%) of 38 cases on the 0.2-T MR system, and good in 32 (84%) and fair in 6 (16%) of 38 cases on the 1.5-T system. Motion artifacts were considered low in 24 (63%) and moderate in 14 (37%) of 38 cases for the 0.2-T system and low in 34 (89%) and moderate in 4 (11%) for 1.5-T system. Based on our results, low-field MR compares favorably to high-field MR in the detection of major abnormalities of the glenohumeral joint, at least when MR arthrography is used. Disadvantages are the duration of the examination and thus the risk of reduced image quality caused by motion artifacts.

Adult↗
PubMed2000

[Noninvasive evaluation of coronary bypass grafts by magnetic resonance imaging. Comparison of the Haste and Fisp-3-D sequences with the conventional coronary angiography].

The aim of the study was to evaluate the patency of coronary artery bypass grafts (CABG) with the 2D and 3D magnetic resonance (MR) imaging techniques. 29 patients with 74 bypass grafts and a total of 91 distal anastomoses were studied on a 1.5 Tesla scanner using a phased array body coil. A 2D T-2 weighted breathhold turbo spin echo sequence (Haste) and a 3D breath hold contrast enhanced MR angiography sequence (Fisp-3-D) were performed. With the Haste and Fisp-3-D sequences 55 of the 58 patent and 15 of the 16 occluded grafts were recognized; the sensitivity and specificity were 95% and 94%, respectively. With the Haste sequence 74% (47/63) and with the Fisp-3-D sequence 64% (40/63) of the distal anastomoses were seen in good image quality. Only 3 of 8 significant grafts stenoses were detected. The patency of CABGs can be evaluated non-invasively with the Haste and the Fisp-3-D angiography sequences. Better results can be expected with the development of a blood-pool contrast medium and the combination of MR flow measurements with imaging techniques.

Aged↗
PubMed2000

Contrast-enhanced MRI of the lung.

The lung has long been neglected by MR imaging. This is due to unique intrinsic difficulties: (1) signal loss due to cardiac pulsation and respiration; (2) susceptibility artifacts caused by multiple air-tissue interfaces; (3) low proton density. There are many MR strategies to overcome these problems. They consist of breath-hold imaging, respiratory and cardiac gating procedures, use of short repetition and echo times, increase of the relaxivity of existing spins by administration of intravenous contrast agents, and enrichment of spin density by hyperpolarized noble gases or oxygen. Improvements in scanner performance and frequent use of contrast media have increased the interest in MR imaging and MR angiography of the lung. They can be used on a routine basis for the following indications: characterization of pulmonary nodules, staging of bronchogenic carcinoma, in particular assessment of chest wall invasion; evaluation of inflammatory activity in interstitial lung disease; acute pulmonary embolism, chronic thromboembolic pulmonary hypertension, vascular involvement in malignant disease; vascular abnormalities. Future perspectives include perfusion imaging using extracellular or intravascular (blood pool) contrast agents and ventilation imaging using inhalation of hyperpolarized noble gases, of paramagnetic oxygen or of aerosolized contrast agents. These techniques represent new approaches to functional lung imaging. The combination of visualization of morphology and functional assessment of ventilation and perfusion is unequalled by any other technique.

Carcinoma, Bronchogenic↗
PubMed2000

[Contrast-enhanced MR angiography of abdominal vessels using a 1.0 T system].

PURPOSE: To evaluate the efficacy of breath-hold, three-dimensional, contrast-enhanced magnetic resonance angiography with a 1.0 T system for imaging the abdominal vessels in comparison to conventional arteriography (CA). METHODS: The abdominal aorta and visceral arteries were studied in 54 patients (60 examinations) on a 1.0 T scanner using an ultrafast gadolinium-enhanced gradient-echo sequence with the following parameters: TR/TE = 3.8/1.4 ms, flip angel 25 degrees, matrix 198 x 256, field 380-420 mm, pixel size 1.9 x 1.48 mm2, slice thickness 1.5-2.5 mm, acquisition time 22-26 sec. Individual circulation times were determined by a test bolus before each MR angiography. Conventional arteriography was performed in 23 of the 60 cases. RESULTS: 172 vessel segments of 23 MR angiographies were compared with CA, sensitivity and specificity were 96.4% and 97.2%. Over-estimations of stenoses or occlusions (n = 4) were caused by the limited resolution of small vessel branches and one stent artifact. CONCLUSION: Contrast-enhanced MR angiography of the abdominal vessels may replace invasive digital subtraction angiography in certain cases like perioperative or peri-interventional diagnostics. Imaging of small peripheral vessels remains a problem and limits use of the method.

Abdomen↗
PubMed2000

[Low-field MRI of the ankle joint: initial experience in children and adolescents using an open 0.2 T MR-system].

PURPOSE: To evaluate the feasibility and diagnostic confidence of MRI with an open low field System (Magnetom open, Siemens, Germany) in children with predominantly traumatic disorders. MATERIAL AND METHODS: Conventional X-rays and MRI examinations have been evaluated in 55 children. MRI was performed at an open 0.2 T MR-unit. The study protocol comprised coronal STIR-sequence, an angulated T2 weighted TSE-sequence and T1 weighted SE-sequence. RESULTS: MRI showed ligamental rupture in 33/50 (60%) cases. Injuries of the ATFL were most frequent (27/33); osseous ligamental tears occurred in approx. 50% of all cases. Fractures of the distal tibia and fibula were diagnosed in 28/55 children. 15/28 cases showed an involvement of the epiphysis. We found occult fractures in 11/28 children. Fractures, diagnosed by conventional x-rays, were excluded in 6 cases. Therapy changed in 35/55 patients on the basis of MRI-findings. CONCLUSION: Low-field MRI of the ankle joint in children and adolescents is able to show numerous pathological conditions. We recommend low-field MRI of the ankle in children with persistent or unclear pain of the ankle joint and inconspicuous conventional x-ray.

Adolescent↗
PubMed2000

[Contrast media enhanced three dimensional MR angiography of the pulmonary arteries in patients with chronic recurrent pulmonary embolism--comparison with selective intra-arterial DSA].

PURPOSE: This study compares contrast-enhanced 3D-MR angiography (MRA) of the pulmonary arteries with selective intra-arterial DSA in patients with chronic thromboembolic pulmonary hypertension. MATERIALS AND METHODS: 20 patients preoperatively underwent a contrast-enhanced 3D-MRA of the pulmonary arteries at 1.5 T using the phased-array body coil. For MRA, we used a 3D-Flash-sequence after bolus timing. 2 radiologists analyzed the acquired image material in consensus with respect to the detection of central thromboembolic material and the visualization of the pulmonary arterial tree. Finally, the MR angiograms were compared with selective DSA images using surgical findings as the definitive standard. RESULTS: MRA demonstrated central thromboembolic material, vessel cut-offs and abnormal proximal-to-distal tapering in all patients. Compared to DSA, MRA depicted the pulmonary vessels up to the segmental level in all cases, it was inferior to DSA in delineation of the subsegmental arteries (sensitivity 87%, specificity 100%). The central beginning of the thromboembolic occlusions seen at MRA corresponded to the beginning of the deobliteration procedure during pulmonary thromboendarterectomy in every case. CONCLUSIONS: Contrast-enhanced 3D-MRA of the pulmonary arteries enables the reliable detection of central thromboembolic material in patients with CTPEH. It also allows identification of those patients who may be treated surgically.

Adult↗
PubMed2000

[Rational diagnostic imaging of pelvic and acetabulum injuries].

In spite of the widespread availability of CT scanners, conventional X-ray radiographs remain the basic imaging modality in patients with pelvic and/or acetabular trauma. However, the extent of their use will depend on local utilities (e.g., availability of CT scanners) and on the patient's clinical condition. Regarding the inaccuracy of conventional radiography in the diagnosis of injuries of the dorsal pelvic ring and of the acetabulum, computed tomography represents the most important imaging modality in the clinically stable patient. CT provides an exact staging of the extent of trauma and allows for differentiation of pelvic instabilities. CT clearly demonstrates the severity of acetabular trauma and is superior in the detection of local complicating factors, i.e., impressions fractures and (sub-)luxations of the femoral head as well as free intraarticular fragments. CT findings provide the basis for definite treatment regimens of the injured patient. By extension of the examination, all relevant organs and systems (craniospinal, cardiovascular, gastrointestinal, respiratory, genitourinary) can be imaged during one session. The speed of spiral CT scanners and their diagnostic accuracy will play a major role in the management of, especially, polytraumatized patients. The indication for angiography with the option of therapeutic embolization exists if a pelvic bleeding persists even after reposition and operative fixation of the injury.

Acetabulum↗
PubMed2000

[In vitro investigation of biological and technical prosthetic heart valves using MRI: evaluation of possible deflection and heating of the implants].

PURPOSE: In vitro evaluation of possible deflection and heating of present-day prosthetic heart valves during MR imaging at 1.5 T. METHODS: 17 prosthetic heart valves, 12 technical and 5 biological, were investigated using a 1.5 Tesla Siemens Vision system. Deflection was measured at the edge of a 1.5 Tesla superconducting magnet. Each valve was then submerged in a vial of a 1/1 electrolyte solution and temperature was measured before and after imaging with a turbo-spin-echo sequence (TR 5200 ms, TE 138 ms, Flip angle 180 degrees, acquisition time 10.5 minutes, length of echo train 29). MR imaging was performed with phase encoding parallel and perpendicular to the plane of the valves. RESULTS: None of the investigated prosthetic heart valves were deflected. The maximal observed temperature rise was 0.5 degree C. During MR investigation of the prostheses, artifacts caused by metallic parts were less evident using a spin-echo sequence than a gradient-echo sequence. CONCLUSIONS: Patients with the tested present-day prosthetic heart valves can be safely imaged by MRI.

Bioprosthesis↗
PubMed2000

[Contrast media-enhanced 3D MR angiography of peripheral arteries using an automatic tracking technique at 1.0 Tesla].

PURPOSE: Assessment of the value of contrast-enhanced MR angiography (ceMRA) using an automatic tracking technique at 1.0 Tesla in comparison with digital subtraction angiography (DSA) of the pelvic and lower limb arteries. MATERIALS AND METHODS: In 15 patients with peripheral arterial occlusive disease a ceMRA (3D FLASH, TR/TE = 6.2/2.3 ms, Flip angle alpha = 30 degrees, Matrix 170 x 256) using a new automatic tracking technique was accomplished. The reference method was DSA. Twenty-one vessel segments of each patient were graded as normal, stenosed (> 50%) or occluded. Image material was evaluated independently by two radiologists. RESULTS: In comparison, the interobserver agreement showed a good (Cohen's kappa > 71%) concordance for 38% of the 21 vessel segments, a moderate (Cohen's kappa between 31%-70%) for 21% and a poor (Cohen's kappa < 30%) concordance for 38% of the 21 vessel segments. Regarding the MRA and DSA results, a good concordance was achieved for 62% of the 21 vessel segments, 14% showed a moderate concordance and 24% only a poor concordance. CONCLUSION: In patients with peripheral arterial occlusive disease ceMRA using an automatic tracking technique enables a reliable evaluation of pelvis and upper limb arteries at 1.0 Tesla. However, a reliable evaluation of lower limb arteries is not yet possible.

Aged↗
PubMed2000

Diabetes and peripheral arterial occlusive disease: prospective comparison of contrast-enhanced three-dimensional MR angiography with conventional digital subtraction angiography.

OBJECTIVE: The purpose of this study was to compare contrast-enhanced three-dimensional MR angiography with conventional digital subtraction angiography (DSA) for identifying and evaluating arteries of the distal calf and foot in diabetic patients with severe arterial occlusive disease who will undergo distal bypass surgery. SUBJECTS AND METHODS: Twenty-four feet of 24 consecutive patients with diabetes and limb-threatening lower extremity ischemia were prospectively imaged using an ultrafast three-dimensional fast low-angle shot sequence on a 1.5-T MR scanner. All patients also underwent DSA of the diseased extremity within 5 days. Images were interpreted in a randomized manner by two observers in conference. Each lower extremity was divided into seven potential arterial segments. Image analysis included the detection of patent, stenosed, or occluded vessel segments. A vascular surgeon formulated treatment plans on the basis of findings from DSA and then formulated treatment plans on the basis of findings from both DSA and MR angiography. RESULTS: MR angiography was significantly better than DSA in revealing peripheral runoff vessels (p < 0.001). In nine (38%) of the 24 patients, MR angiography showed patent pedal vessels suitable for distal bypass grafting that were not revealed by DSA. Because of the results of MR angiography, treatment plans changed in seven of the nine patients in whom patent vessels were subsequently used as target vessels for distal pedal bypass grafts. CONCLUSION: Contrast-enhanced three-dimensional MR angiography is superior to DSA in revealing patent vessel segments of the foot in diabetic patients with severe arterial occlusive disease. Contrast-enhanced three-dimensional MR angiography should be part of the diagnostic algorithm for patients in whom pedal bypass grafting is a therapeutic option.

Aged↗
PubMed1999

[Value of MRI in diagnosis of occult fractures].

The term "occult fracture" defines the lack of visible fracture signs in conventional radiography although a fracture exists. The diagnosis is made in the sequel or through further diagnostic procedures. The use of scintigraphy and CT examinations is limited by their moderate sensitivity and specificity. In contrast, MRI is a diagnostic tool that allows early diagnosis of a fracture and of accompanying chondral or ligament damage. We report on 23 patients with traumatic fractures at 5 different anatomical sites, all of which were negative by x-ray, but the diagnosis could subsequently be made with MRI.

Adolescent↗
PubMed1999

Injuries of the lateral collateral ligaments of the ankle: assessment with MR imaging.

The aim of this study was to evaluate the ability of MRI to display injuries of the lateral collateral ligamentous complex in patients with an acute ankle distorsion trauma. The MR examinations of 36 patients with ankle pain after ankle distorsion were evaluated retrospectively without knowledge of clinical history, outcome and/or operative findings. The examinations were performed on a 1. 5-T whole-body imager using a flexible surface coil. The signs for ligamentous abnormality were as follows: complete or partial discontinuity, increased signal within, and irregularity and waviness of the ligament. The results were compared with operative findings in 18 patients with subsequent surgical repair. Eighteen patients with conservative therapy had a follow-up MR examination after 3 months. There was 1 sprain, 3 partial and 32 complete tears of the anterior talofibular ligament, and 5 sprains, 5 partial, and 7 complete tears of the calcaneofibular ligament. There were no lesions of the posterior talofibular ligament. Compared with surgery, MRI demonstrated in 18 of 18 cases the exact extent of anterior talofibular ligament injuries and underestimated the extent in 2 of 8 cases of calcaneofibular ligament injury. In patients with follow-up MRI after conservative therapy, a thickened band-like structure was found along the course of the injured ligament in 17 of 18 cases. The absence of ligament repair after conservative treatment was confirmed during operative revision in one case. The MRI technique allows for grading of the extent of injury of the lateral collateral ligamentous complex after acute ankle strain. It seems to be suitable for monitoring the healing process after conservative-functional treatment of ligament tears.

Acute Disease↗
PubMed1999

Unusual manifestation of an osteoid osteoma of the capitate.

A case of osteoid osteoma of the capitate in a 29-year-old male is reported. The patient suffered from unspecific clinical findings and a 3-year history of uncharacteristic wrist pain. Conventional radiographs of the wrist revealed a circumscribed sclerosis in the proximal part of the capitate bone beside a diffuse demineralisation of the carpal bones. Magnetic resonance imaging demonstrated a circumscribed, tumorous lesion with marked enhancement after IV administration of contrast agent and a highly calcified nidus, which was sharply demarcated by a small rim of granulation tissue from the surrounding spongious bone. Based on MRI findings, the diagnosis of an osteoid osteoma was established and confirmed after operation and histologic analysis.

Adult↗
PubMed1999

MRI of the pulmonary parenchyma.

Imaging of the pulmonary parenchyma represents a unique challenge for MRI. Limited signal is caused by low proton density, susceptibility artifacts, and physiological motion (cardiac pulsation, respiration). Recently, further improvements in MRI techniques have widened the potential for investigations of pulmonary parenchymal disease. These include very short echo times, ultrafast turbo-spin-echo acquisitions, projection reconstruction technique, breathhold imaging, ECG triggering, contrast agents (perfusion imaging, aerosols), sodium imaging, hyperpolarized noble gas imaging, and oxygen enhancement. By using widely available techniques, MRI is helpful in the assessment of (a) acute alveolitic processes in chronic infiltrative lung disease, (b) detection and characterization of pulmonary nodules, (c) detection, characterization, and follow-up of pneumonia, (d) differentiation of obstructive atelectasis from non-obstructive atelectasis and infarctions, and (e) measurements of lung water content. Chronic bronchitis, bronchiectasis, and emphysema are not readily assessable by routine MRI techniques. More sophisticated techniques are under investigation for MR imaging of pulmonary ventilation and perfusion. They represent the beginning of functional MR imaging of the lung which will be established in the future.

Contrast Media↗
PubMed1999

[Diagnosis of an intramyocardial hematoma via MRI after a traumatic myocardial infarct].

Traumatic cardiac lesions occur in about 30% of all traumatized patients, in most cases they are due to traffic accidents. We report a patient who suffered from a traumatic anterior wall infarction following a ski accident. Consecutively, an extended intramyocardial hemorrhage occurred. A left ventricular pseudoaneurysm was considered first by echocardiography. Using MRI, an intramyocaridal hemorrhage could be diagnosed because of a thin myocardial border surrounding the hematoma. Consecutively, the patient underwent CABG surgery as well as a resection of the intramyocardial hematoma. This diagnosis could be manifested surgically and histologically.

Aged↗