Biomedical subjects

M Thelen

Publications and source records attributed to M Thelen.

At least 37 records · Page 2Linked to original sources

PubMed2004

[Fully automatic detection and quantification of emphysema on thin section MD-CT of the chest by a new and dedicated software].

PURPOSE: Introduction of a novel software tool (YACTA -- yet another CT analyzer) for detection and quantification of pulmonary emphysema in thin-slice chest MDCT data sets. MATERIALS AND METHODS: Consisting of grey-level threshold-based algorithms (e. g., region-growing), expert rules and morphological image postprocessing YACTA segments the tracheobronchial tree prior to the detection and quantification of pulmonary emphysema. In addition to general parameters, such as the mean lung density (MLD) and the emphysema index (EI -- also described as pixel index PI), the previously described bullae index (BI) is transformed into a three-dimensional parameter for a morphological description of emphysema. A first evaluation of chest MDCT data sets of 11 patients was performed as well as a comparison of MLD, lung volume (LV), emphysema volume (EV) and PI calculated with two established commercial tools of Siemens Medical Solutions (Volume and Pulmo). Furthermore, the BI was calculated with YACTA. RESULTS: YACTA processed the image data without manual interaction and demonstrated more user-comfort than Volume and Pulmo software, which require manual correction especially for lung segmentation at the hilar regions to separate central airways from lung parenchyma. MLD, LV, and EV values calculated with YACTA were systematically higher (Pulmo: + 50 HU/+ 597 ml/+ 159 ml; Volume: + 32 HU/+ 110 ml/+ 155 ml). Different segmentation algorithms are responsible for this: YACTA includes areas not assessed by mere threshold-based techniques. Constantly lowered LV values of Pulmo are caused by a missing dilatation algorithm. The error correction as a special feature of YACTA results in increased emphysema volumes and indices. The segmentation of the tracheobronchial tree lowers the part of airways falsely classified as emphysema. CONCLUSION: The new developed software shows higher user comfort as established by semi-automated tools. RESULTS: of LV, EV, MLD and PI are comparable or moderately different. Automatic calculation of a BI is possible, providing information about bullous morphology of pulmonary emphysema. Further studies are necessary to correlate data with clinical or pathological parameters.

Adult↗

PubMed2004

[CT-angiography with a 16-row CT scanner for perioperative evaluation of the hepatic arteries].

PURPOSE: To evaluate the efficiency of CT angiography (CTA) with 16-row MSCT compared with MR angiography (MRA) in analyzing the arterial anatomy in patients undergoing liver surgery. MATERIALS AND METHODS: In 30 patients, MRA and CTA studies of the abdominal vessels were reviewed. CT parameters: slice thickness 3 mm; collimation 1.5; reconstruction interval 2 mm (Philips MX 8000 IDT); 120 ml contrast media (400 mg/ml) at a rate of 4 ml/sec; acquisition of arterial-phase scans. The anatomy of the hepatic artery was evaluated from axial and reconstructed maximum-intensity-projection (MIP) images ("Slab-Viewer", Philips). MR parameters: contrast-enhanced coronal FLASH-3D sequences; slice thickness 1.4 mm; TR 3.47, TE 1.3; 1.5 T scanner (Siemens Somatom). Image quality was rated with a scoring system. Contrast enhancement of the hepatic artery and the liver parenchyma was measured. RESULTS: The image quality of CTA was rated as excellent in 18 (MRA 5); good in 8 (MRA 22); satisfactory in 4 patients (MRA 3), and non-diagnostic in 0 patient (MRA 1). Compared to MRA, the image quality of CTA was better in 15/30 patients; equal for both in 13 and worse in 2 patients. CTA provided a better depiction of the segmental branches of the hepatic arteries in 15/30 patients and revealed important anatomic variations of the hepatic artery in 8/30 patients. These variations were not be seen in MRA: e. g., MRA missed a left gastric arterial supply to the left liver. The ratio of contrast enhancement in liver parenchyma and hepatic artery was 4.7 in CTA and 4.5 in MRA. CONCLUSION: CTA with multislice scanners delivers better image quality and depiction of the hepatic arteries than MRA. Thus, MRI of the hepatic arteries can be replaced by routine CT, which is already part of the preoperative evaluation for liver transplantation.

Angiography↗

PubMed2004

[Diagnostic imaging of hilar cholangiocarcinoma: preoperative evaluation of ERC, MRC and PTC in comparison with histopathology].

PURPOSE: To compare the results of the preoperative workup consisting of endoscopic retrograde cholangiography (ERC), magnetic resonance cholangiography (MRC), and percutaneous resonance cholangiography (PTC) with the tumor extent of the surgical specimen in patients with hilar cholangiocarcinoma (hilCC). MATERIALS AND METHODS: Between 9/1997 and 12/2002, 59 patients with hilCC tumor underwent surgical resection. Preoperative ERC, MRC, and PTC were analyzed, blinded for the identity of the patient, and compared with the surgical specimen. For this retrospective analysis, 55 of the initial 59 ERCs, 39 of the initial 40 MRCs and 32 of the initial 38 PTCs were available. Most of the ERCs and MRCs had been performed at referring institutions by various investigators. In 20 patients, all three imaging modalities were available for direct comparison. RESULTS: The mean scores of the visualization of the bile ducts and tumor differ considerably for ERC, MRC and PTC, with PTC visualizing the bile ducts better than ERC (p < 0.001) and MRC (p = 0.019). The tumor classification according to Bismuth and Corlette was correctly predicted by ERC in 29 %, by MRC in 36 % and by PTC in 53 %. The tumor extent was overestimated in 40 % (ERC), 41 % (MRC) and 31 % (PTC) and underestimated in less than 10 % for all modalities. Twenty patients, who underwent all three imaging modalities, were included in an additional analysis for a direct comparison of ERC, MRC and PTC. PTC provided correct or acceptable information on tumor extent in 19 of 20 patients, MRC in 15 of 20 patients, and ERC in only 11 of 20 patients. The statistical analysis revealed a significant superiority of PTC to ERC (McNemar test: p < 0.01) but not to MRC (p = 0.22). DISCUSSION: The management of patients with hilar cholangiocarcinoma requires a high degree of expertise in diagnostic imaging techniques. Cholangiography should not only define the location but also visualize the uppermost extent of the tumor to determine resectability. In contrast to most reports in the literature, ERC and MRC were found to be of limited reliability regarding the assessment of the tumor extent. ERC may be more and more reserved for patients considered for nonsurgical intervention or palliation. PTC proved to be the most reliable approach. MRC represents a noninvasive diagnostic tool for the evaluation of malignant perihilar biliary obstructions, but should be performed at highest quality using state-of-the-art MRI techniques. The most common mistake of each diagnostic modality was an overestimated tumor extent, which may exclude patients from potentially curative surgery.

Aged↗

PubMed2004

[Assessment of global and regional left ventricular function with a 16-slice spiral-CT using two different software tools for quantitative functional analysis and qualitative evaluation of wall motion changes in comparison with magnetic resonance imaging].

PURPOSE: To determine global and regional left ventricular (LV) function from retrospectively gated multidetector row computed tomography (CT) by using two different semiautomated analysis tools and to correlate the results with those of magnetic resonance imaging (MRI). MATERIALS AND METHODS: Nineteen patients (5 females, 14 males, mean age 69 years) underwent 16-slice spiral-CT (MS-CT) with standard technique without administration of beta-blockers for a decrease in the cardiac rate. Ten series of images were reconstructed at every 10 % of the RR-interval. With commercially available software capable of semiautomated contour detection, end-diastolic and end-systolic LV volumes (EDV and ESV) were determined from short-axis multiplanar CT reformations (MPR). Axial images of the end-systolic and end-diastolic cardiac phase were transformed to 3D volumes (3D) to determine EDV and ESV by using a threshold-supported reconstruction algorithm dependent on the contrast enhancement of the left ventricle. Steady-state free-precession cine MR images were acquired in short-axis orientation on the same day in all but one patient. Regional wall motion was assessed qualitatively in 17 left ventricular segments and classified as normo-, hypo-, a- or dyskinetic. Bland-Altman analysis was performed to calculate limits of agreement and systematic errors between CT and MRI. RESULTS: For MPR/3D, mean end-diastolic (144.4/142.8 mL +/- 67.5/67.1) and end-systolic (66.4/68.7 mL +/- 52.1/49.9) LV volumes as determined with MS-CT correlated well with MRI measurements (147.6 mL +/- 67.6 [ r = 0.98/0.96] and 73.3 mL +/- 55.5 [ r = 0.98/0.98], respectively [ p <.001]). LV stroke volume (77.6/74.1 +/- 19.2/23.4 mL for CT vs. 74.4 mL +/- 18.4 for MRI, r = 0.92/0.74) and LV ejection fraction (58.6/55.9 % +/- 13.5/13.7 for CT vs. 55.6 % +/- 13.5 for MRI, r = 0.95/0.91) also showed good correlation (p <.001). Regional wall motion analysis revealed agreement between CT and MRI in 316/323 (97.8 %) myocardial segments. CONCLUSION: Semiautomated analysis of 16-detector row CT data sets enables global and regional volumetric and functional analysis. The CT results correlate well with MRI findings for short axis MPR and for 3D volume reconstructions, with a higher statistical spread for the 3D method. The underestimation of end-systolic and end-diastolic volumes with CT may be caused by partial volume averaging due to the lower temporal resolution as compared with MRI.

Aged↗

PubMed2004

[Evaluation of a new software tool for the automatic volume calculation of hepatic tumors. First results].

PURPOSE: Computed tomography has become the preferred method in detecting liver carcinomas. The introduction of spiral CT added volumetric assessment of intrahepatic tumors, which was unattainable in the clinical routine with incremental CT due to complex planimetric revisions and excessive computing time. In an ongoing clinical study, a new software tool was tested for the automatic detection of tumor volume and the time needed for this procedure. MATERIALS AND METHODS: We analyzed patients suffering from hepatocellular carcinoma (HCC). All patients underwent treatment with repeated transcatheter chemoembolization of the hepatic arteria. The volumes of the HCC lesions detected in CT were measured with the new software tool in HepaVison (MeVis, Germany). The results were compared with manual planimetric calculation of the volume performed by three independent radiologists. RESULTS: Our first results in 16 patients show a correlation between the automatically and the manually calculated volumes (up to a difference of 2 ml) of 96.8 %. While the manual method of analyzing the volume of a lesion requires 2.5 minutes on average, the automatic method merely requires about 30 seconds of user interaction time. CONCLUSION: These preliminary results show a good correlation between automatic and manual calculations of the tumor volume. The new software tool requires less time for accurate determination of the tumor volume and can be applied in the daily clinical routine.

Algorithms↗

PubMed2003

Evaluation of changes in central airway dimensions, lung area and mean lung density at paired inspiratory/expiratory high-resolution computed tomography.

The aim of this study was to improve the understanding of interdependencies of dynamic changes in central airway dimensions, lung area and lung density on HRCT. The HRCT scans of 156 patients obtained at full inspiratory and expiratory position were evaluated retrospectively. Patients were divided into four groups according to lung function tests: normal subjects ( n=47); obstructive ( n=74); restrictive ( n=19); or mixed ventilatory impairment ( n=16). Mean lung density (MLD) was correlated with cross-sectional area of the lung (CSA(L)), cross-sectional area of the trachea (CSA(T)) and diameter of main-stem bronchi (D(B)). The CSA(L) was correlated with CSA(T) and D(B). MLD correlated with CSA(L) in normal subjects ( r=-0.66, p<0.0001) and patients with obstructive ( r=-0.62, p<0.0001), restrictive ( r=-0.83, p<0.0001) and mixed ventilatory impairment ( r=-0.86, p<0.0001). The MLD correlated with CSA(T) in the control group ( r=-0.50, p<0.0001) and in patients with obstructive lung impairment ( r-0.27, p<0.05). In patients with normal lung function a correlation between MLD and D(B) was found ( r=-0.52, p<0.0001). CSA(L) and CSA(T) correlated in the control group ( r=0.67, p<0.0001) and in patients with obstructive lung disease ( r=0.51, p<0.0001). The CSA(L) and D(B) correlated in the control group ( r=0.42, p<0.0001) and in patients with obstructive lung disease ( r=0.24, p<0.05). Correlations for patients with restrictive and mixed lung disease were constantly lower. Dependencies between central and peripheral airway dimensions and lung parenchyma are demonstrated by HRCT. Best correlations are observed in normal subjects and patients with obstructive lung disease. Based on these findings we postulate that the dependencies are the result of air-flow and pressure patterns.

Adolescent↗

PubMed2003

[Indirect MR-arthrography in the follow up of autologous osteochondral transplantation].

PURPOSE: To evaluate the spectrum of findings in indirect MR-arthrography following autologous osteochondral transplantation. PATIENTS AND METHODS: 10 patients with autogenous osteochondral homografts underwent indirect MR-arthrography at three, 6 and 12 months postoperatively. The MR protocol at 1.5 T comprised unenhanced imagings with PD- and T2 -weighted TSE- sequences with and without fat-suppression as well as T1 -weighted fat-suppressed SE-sequences before and after i.v. contrast administration and after active joint exercise. Image analysis was done by two radiologists in conference and comprised the evaluation of signal intensity (Sl) and integrity of the osseous plug and the cartilage surface, as well as the presence of joint effusion or bone marrow edema. RESULTS: At three months, all cases demonstrated a significant bone marrow edema at the recipient and donor site that corresponded to a significant enhancement after i.v. contrast administration. The interface between the transplant and the normal bone showed an increased Sl at three and 6 months in T2 -weighted images as well as in indirect MR-arthrography. The marrow signal normalized in most cases after 6 to 12 months, indicating vitality and healing of the transplanted osteochondral graft. The Sl of the interface decreased in the same period, demonstrating the stability of the homograft at the recipient site. The osteochondral plugs were well-seated in 9/10 cases. Indirect MR-arthrography was superior to unenhanced imaging in the assessment of the cartilage surface. Cartilage coverage was complete in every case. The transplanted hyaline cartilage as well as the original cartilage showed a significant increase of the Sl in indirect MR-arthrography, that did not change in follow up studies. There were no pathological alterations of signal and thickness alterations of the transplanted cartilage in follow up investigations. CONCLUSION: Indirect MR-arthrography is a useful diagnostic tool following autologous osteochondral transplantation. Assessment of transplant vitality, osseous fixation and stability is possible.

Adolescent↗

PubMed2003

Pulmonary balloon angioplasty of chronic thromboembolic pulmonary hypertension (CTEPH) in surgically inaccessible cases.

The clinical course of patients suffering from chronic thromboembolic pulmonary hypertension (CTEPH) depends on the distribution pattern of the thromboembolic material. In patients with thromboembolic findings in the central pulmonary segments pulmonary thrombendarterectomy (PTE) has excellent results and acceptable operative risk. This paper presents two surgically inaccessible cases that were successfully treated with balloon pulmonary angioplasty. Balloon angioplasty improved parenchymal perfusion, increased cardiac index (Delta CI +19.2 % [Case 1], and +15.4 % [2]), reduced pulmonary vascular resistance during follow-up (Delta PVRI -25.0 % [1] and -15.9 % [2]), and is discussed as an alternative treatment option for cases not suited for surgery.

Adult↗

PubMed2003

[Endovascular therapy of abdominal aortic aneurysm: results of a mid-term follow-up].

PURPOSE: Prospective study to evaluate clinical results and complications of endovascular abdominal aortic aneurysm treatment in a mid-term follow-up. MATERIALS AND METHODS: A total of 122 patients (9 females, 113 males, average age 70.9 +/- 7.9 years) with abdominal aortic aneurysms were treated with stent grafts (53 Vanguard or Stentor endografts, 69 Talent endografts). Group I consisted of 40 patients who had all aortic tributaries of the aneurysm sac occluded prior to endovascular grafting, either spontaneously by parietal thrombosis or by selective coil embolization of the respective ostia preserving collateral circulation distal to the vessel occlusion. Group II consisted of 82 patients and included all cases without or with incomplete coil embolization with at least one patent vessel. Stent grafting was performed in general anesthesia in the first 21 patients, followed by peridural anesthesia in 15 cases, and local anesthesia with conscious sedation in 86 cases. The results were evaluated with Spiral-CT, MRI and radiographs of the endovascular graft, with follow-up examinations obtained at 3, 6, 12 months, and every year. RESULTS: Implantation was successfully completed in all cases without primary conversion surgery, laparotomy, or any significant complication. Mean follow-up was 29 +/- 21 months (maximum 84 months). The 30-day mortality was 0.8 % due to a myocardial infarction 3 days after discharge from the hospital. A total of 47 re-interventions were performed in 29 patients (23.8 %), with 35 re-interventions in 18 cases with Vanguard or Stentor endografts and 12 re-interventions in 11 patients with Talent endografts. 23 percutaneous re-interventions included distal graft extension (n = 11), Wallstents for kinking and limb stenosis (n = 3), and secondary coil embolization of collateral vessels (n = 9). 24 surgical re-interventions included proximal graft extension (n = 6), new endovascular grafts (n = 3), surgical clipping of lumbar and mesenteric artery branches for type-II endoleaks following ineffective secondary coil embolization (n = 1), and femorofemoral crossover bypasses (n = 4). A total of 10 secondary conversion operations were performed because of damage to the membrane (n = 4; 3 Vanguard endografts, 1 Talent endograft), significant caudal migrations (n = 5; 4 Vanguard endografts, 1 Talent endograft) associated with type-I endoleaks (n = 2), limb occlusion (n = 1), disconnection of graft components (n = 1), and significant endoluminal thrombus deposits (n = 1). One patient, who was followed for 82 months, suffered from a significant endoleak for 10 months with increasing aneurysm diameter but he refused surgery. He was admitted with aneurysm perforation and was successfully operated with aortic graft replacement. Compared to group II, the incidence and size of endoleaks was reduced in group I (incidence 19.2 % versus 29.9 %, p < 0.05). Group I demonstrated significantly better aneurysm shrinkage at 36 months follow-up (Delta sagittal diameter - 11.1 +/- 8.4 mm versus - 4.9 +/- 6.2 mm, p < 0.05). CONCLUSION: In selected patients, endovascular aneurysm treatment is an effective alternative to open surgery. It is safely performed in local anesthesia with low mortality rate and a low number of acute complications. Intermediate follow-up revealed re-interventions in around one quarer of all patients, especially when Vanguard or Stentor endografts were implanted. Primary coil embolization of all aortic branches prior to endovascular grafting improves clinical outcome. Insufficient proximal fixation and its consecutive complications remains a major problem of this method.

Aged↗

PubMed2003

[Measurement of the AT and the CCD angle of macerated cadaver femora: a comparative study between CT and MRI measurements].

PURPOSE: To compare measurements of the real AT (femoral antetorsion) and CCD (caput-collum-diaphysis) angle by computed tomography (CT) and magnetic resonance imaging (MRI) of hip specimen using direct measurements as reference standard, and to show that measurement by MRI can replace CT measurements and may help avoiding X-ray exposition. MATERIALS AND METHODS: CT and MRI measurements were obtained on 25 in water-arrested macerated human femora. Postprocessing was done by 4 independent readers on a workstation using a dedicated 3D-software. Direct measurements of the real AT and the CCD angle were used as reference standard. The analysis included Student's t test for paired values, interobserver variability using intra-class correlation coefficients (ICC), maximum and middle divergence of the angles, and Bland-Altman plots. RESULTS: For determining AT and the CCD angle with CT and MRI, good correlation was found between the 4 readers and with measurements using the reference standard. ICCs were 0.97 and 0.90 for measuring AT and CCD angle with CT, and 0.95 and 0.71 for measurements with MRI, respectively. Mean divergence between CT measurements and those of the reference standard was 0.8 degrees for AT and 0.7 degrees for the CCD-angle. Mean divergence between MRI measurements and those of the reference standard was 0.3 degrees for AT and -0.4 degrees for the CCD-angle. Mean divergences between CT and MRI measurements of AT and CCD-angle were 0.5 degrees. Neither systematic errors nor dependences on the qualitative size of the reference data were evident in the divergences of measurements. CONCLUSION: Measurements of the real AT and CCD angle by CT and MR imaging revealed a good correlation with direct measurements of the femoral specimen and consequently can be recommended for clinical use. MRI measurements can replace CT measurements, avoiding X-ray exposure especially in young patients undergoing preoperative evaluation for hip dysplasia.

Bone Malalignment↗

PubMed2003

[Computer aided diagnosis in chest radiology - current topics and techniques].

The proliferation of digital data sets and the increasing amount of images, e. g. through the use of multislice spiral CT or multiple follow-up examinations in the context of new therapies, are ideal prerequisites for computer-aided diagnosis (CAD) in chest radiology. Multiple studies have described the applications and advantages of computer assistance in performing different diagnostic tasks. More powerful computers will enable the introduction of these systems into the clinical routine and could provide an enormous increase in morphological and functional information. The commercial introduction of tools for detection and visualization of pulmonary nodules has already begun. This is one of the most widely-reported applications in view of the ongoing studies on lung cancer screening. The next generation of tools will improve the diagnosis of emphysema through detection, quantification and classification. Many more uses are being developed, for instance the detection and classification of infiltrates, volume measurements or functional pulmonary imaging (e. g. dynamic ventilation CT or (3)Helium-MRI). Grossly simplified, most systems use a three level structure consisting of segmentation/feature extraction, classification of extracted features and an output unit. The output can be mere visualization through color-coding, volume measurements or calculated probabilities. The output supports the radiologist in establishing his findings and preparing differential and final diagnoses as well as providing quantitative data for follow-up studies. Different techniques are used for segmentation of lung areas as the basis for a variety of applications. Some commonly-used techniques for this and other tasks are density masks and threshold-based algorithms. Data processing is predominantly carried out with Bayesian classifiers or neural networks. This article describes the current status of research and provides insight into the common schemes and capabilities of the systems. It focuses particularly on common topics such as segmentation, volume measurement, detection of pulmonary nodules, quantification of emphysema and analysis of ground glass opacities.

Diagnosis, Computer-Assisted↗

PubMed2003

[Percutaneous radiofrequency ablation of liver tumors using the LeVeen 4 cm array probe].

BACKGROUND: The purpose of this study was to evaluate safety and efficacy of a radiofrequency ablation system in clinical practice. METHODS: In 35 patients (age 63,9 +/- 12,6 years, range 22 - 83) a total of 65 liver tumors were percutaneously treated using a 200 watt radiofrequency generator and a LeVeen 4 cm array probe (RF3000, Boston Scientific). The interventions were performed under CT guidance in local anaesthesia and sedation. Adapted to the tumor size, the LeVeen Probe was repositioned during the procedure with an additional safety margin of 1 cm. Primary tumors were colorectal in 22, and mamma tumors (n = 4), zystic pancreas tumors (n = 2), gastric cancer (n = 1), zystadenocarcinoma of the liver (n = 1), lung cancer (n = 1), gastrointestinal stroma tumor (n = 1), duodenal carcinoma (n = 1), cholangiocellular carcinoma (n = 1) and hepatocellular carcinoma (n = 1). Post interventional control and follow-up was performed with multislice-CT (collimation 2.5 mm, unenhanced and contrast enhanced, arterial and portal filling) at 4 weeks, and every three months. RESULTS: One to 4 metastases were treated per patient during one or up to 4 procedure sessions. Mean lesion size was 2,3 +/- 1,2 cm (range 0,2 to 7,0). The corresponding size of the necrosis achieved was 4,6 +/- 1,4 cm (range 2,0 - 8,2). Primary technical success with complete tumor ablation was reached in 60 of 65 lesions. In 4 cases two treatment sessions were necessary in order to achieve the intended results. In one case the procedure was aborted because of a close relationship between lesion and right colon. 63 tumors were treated in sedation and local anesthesia. General anesthesia was necessary in two cases, in one who refused intervention in sedation, and in another case with insufficient analgetic effect. Morbidity was 9.2 %: Bleeding complications (n = 3, one arterial bleeding from the ablation tract, two intrahepatic bleedings with extrahepatic hematoma) were confirmed by selective angiography of the hepatic artery and were treated with coil embolisation of the respective segmental arteries. One case with subcapsular tumor ablation suffered from a large subcapsular hematoma requiring a blood transfusion. In one case with a subphrenic location of the metastasis, the needle electrode had passed the costophrenic recessus and resulted in an hematothorax. This patient was treated by pleural drainage for two days. One patient suffered from fever up to 39 degrees C and inflammation of the biliary tract and received a cholecystectomy 22 days post interventionally. There was no peri interventional mortality. Mean follow-up is 5,6 +/- 3,3 months (range 0 to 13). 21 of 35 patients showed no evidence of tumor recurrence. One case is scheduled for a second treatment session for complete tumor ablation. 13 of 35 patients suffered from tumor recurrence, either local recurrences and/or new metastases. At the sites of prior RF-ablation 9 local recurrences were detected in 7 patients, two cases with isolated local recurrences and 5 cases with local recurrences and new metastases. 6 Patients showed no evidence for local recurrences but new metastases. In these 11 cases a total of 37 metastases were found at new locations. In three patients tumor recurrence was treated by means of a second RF-ablation. The remaining 10 patients received chemotherapy. CONCLUSION: RF-ablation can be performed in local anaesthesia and sedation with low peri interventional morbidity and mortality. Using the LeVeen probe and a 200 watt generator, appropriate necroses can be achieved. CT follow-up is required every three months because of the tumor recurrence rate and reinterventions may be required.

Adult↗

PubMed2003

[Influence of endoleaks on aneurysm volume and hemodynamics after endovascular aneurysm repair].

PURPOSE: To evaluate the aneurysm volume and the intra-aneurysmatic pressure and maximal pressure pulse (dp/dtmax) in completely excluded aneurysms and cases with endoleaks. MATERIALS AND METHODS: In 36 mongrel dogs, experimental autologous aneurysms were treated with stent-grafts. All aortic side branches were ligated in 18 cases (group I) but were preserved in group II (n = 18). Aneurysm volumes were calculated from CT scans before and after intervention, and from follow-up CT scans at 1 week, 6 weeks and 6 months. Finally, for hemodynamic measurements, manometer-tipped catheters were introduced into the excluded aneurysm sac (group I and II), selectively in endoleaks (group II), and intraluminally for aortic reference measurement. Systemic hypertension was induced by volume load and pharmacologic stress. Pressure curves and dp/dt were simultaneously recorded and the ratios of aneurysm pressure to systemic reference pressure calculated. RESULTS: At follow-up, type-II. endoleaks were excluded in all cases of group I by selective angiography. In contrast, endoleaks were evident in all cases of group II. Volumetric analysis of the aneurysms showed a benefit for group I with an improved aneurysm shrinkage: DeltaVolume + 0.08 %, - 1.62 % and -9.76 % at 1 week, 6 weeks and 6 months follow-up (median, group I), compared to + 1.43 %, + 0.67 %, and - 4.04 % (group II), p < 0.05. In case of complete aneurysm exclusion the ratio of systolic aneurysm pressure to systemic reference pressure was 0.662, 0.575 and 0.385 (median) at 1 week, 6 weeks and 6 months. The corresponding dp/dtmax ratios were 0.12, 0.07 and 0.04, respectively. However, within endoleaks selective measurements showed significantly increased pressure load: the ratios of systolic endoleak pressure to systemic reference pressure and the corresponding ratios for dp/dtmax were 0.882 and 0.913 (median), respectively. These hemodynamic findings were linear from hypotension, physiologic blood pressure to hypertension. CONCLUSION: Occlusion of all aortic side branches of an aneurysm prior to stent-grafting reduces endoleaks and promotes aneurysm shrinkage. Complete aneurysm exclusion significantly reduces systolic pressure and dp/dt max. In contrast, endoleaks showed nearly systemic pressure load and undamped pulsatility.

Alloys↗

PubMed2003

[Automatic classification of liver segments according to Couinaud: development of a new algorithm and evaluation spiral CT data].

PURPOSE: To develop a software tool that analyzes the anatomy of the portal vein branches and assigns segmental and subsegmental branches according to Couinaud's classification system and to evaluate its accuracy. MATERIALS AND METHODS: The algorithm was developed in C++ on a PC. The algorithm recognizes the three major branching patterns of the portal vein. Segmental and subsegmental branches are assigned to 8 segments following Couinaud and encoded by 8 colors. The software was evaluated using CT data sets of 39 patients. After the individual segmental anatomy of each patient was determined by an experienced radiologist, automatic classification was performed and the results were compared on a branch by branch basis. RESULTS: The numbering was accurate according to Couinaud's system in 358 of 409 segmental and subsegmental branches (88 %). The assignment failed in 51 of 409 branches due to unexpected anatomy or software problems. CONCLUSION: Automatic classification of portal vein branches and their appendant parenchyma is possible. The automatic designation of liver segments enables the three-dimensional visualization of the segmental anatomy. In the future, automatic analysis might facilitate the reporting and communication of CT findings.

Algorithms↗

PubMed2003

[Pre- and postoperative assessment of hemodynamics in patients with chronic thromboembolic pulmonary hypertension by MR techniques].

PURPOSE: To evaluate the potential of MRI to grade cardiac impairment and pulmonary hypertension in patients with chronic thromboembolic pulmonary hypertension (CTEPH) in comparison with invasive pressure measurements before and after surgery. MATERIALS AND METHODS: We examined 35 patients with CTEPH before and after pulmonary thromboendarterectomy (PTE). For assessment of hemodynamics, velocity-encoded segmented GE-sequences (pulmonary arteries and ascending aorta) and segmented cine GE-sequences along the short axis of the heart were performed. The analysis comprised calculation of ejection fractions, peak velocities, mean pulmonary arterial flow and vessel diameter. 10 volunteers served as controls. Flow measurements were compared to invasively measured mean pulmonary arterial pressure (MPAP) and vascular resistance (PVR). RESULTS: Compared to volunteers, CTEPH-patients showed significantly reduced right ventricular ejection fractions (p < 0.001), pulmonary peak velocity (p < 0.001) and significantly increased diameters of the pulmonary arteries (p < 0.001). The flow measurements in the aorta (2713 ml/min) and the pulmonary arteries (2088 ml/min) revealed a large bronchopulmonary shunt. After PTE, there was a significant reduction in vessel diameter (p < 0.001). This was associated with a significant increase in pulmonary peak velocities (p < 0.001). The increase in pulmonary peak velocities correlated with the decrease of PVR (r = 0.5) and MPAP (r = 0.6). The ejection fraction of the right ventricle correlated with PVR (r = 0.6) and MPAP (r = 0.7). The postoperative decrease in MPAP correlated with the increase in right ventricular ejection fraction (r = 0.8). After PTE there was no bronchopulmonary shunt volume. All patients had an inverse motion of the interventricular septum. It returned to normal in 68 % of patients after surgery. CONCLUSION: Breath-hold MR-techniques enable non-invasive assessment of pulmonary hemodynamics in patients with CTEPH. For postoperative follow-up studies MRI could be considered the modality of choice.

Adult↗

PubMed2003

Late improvement of regional wall motion after the subacute phase of myocardial infarction treated by acute PTCA in a 6-month follow-up.

BACKGROUND: The aim of this follow-up study was to investigate the late effects of acute coronary angioplasty (PTCA) on regional wall motion after the subacute phase of myocardial infarction (MI). METHODS AND RESULTS: Seventeen patients were investigated initially at a median of 11 days and again at 6 months after acute PTCA for myocardial infarction (< 8 hours after onset of symptoms) by cardiac magnetic resonance imaging. Corresponding short-axis slices encompassing the left ventricle (LV) were acquired using a standard cine MR for regional wall motion analysis and using delayed contrast enhanced magnetic resonance imaging (ceMRI) for infarct size quantification. The infarct size was similar in the subacute phase and the 6 month follow-up (20.8 and 21.9%, respectively; n.s.). Regional wall motion improved significantly in the area of hyperenhancement [percentage wall thickening (PWT) 21.9% and 37.9%, p < 0.05] in contrast to remote normal myocardium (46.4% and 38.4%; n.s.). Regional wall motion was significantly poorer in transmural compared with nontransmural MI in the subacute stage, and a late improvement could only be observed in transmural MI. CONCLUSION: Transmural areas of hyperenhancement displayed significant late long-term improvement of regional wall motion after acute PTCA, possibly related to prolonged stunning compared with nontransmural areas.

Adult↗

PubMed2003

Lung density distribution in dynamic CT correlates with oxygenation in ventilated pigs with lavage ARDS.

BACKGROUND: Fast dynamic computed tomography (dCT) has been used to assess regional dynamics of lung inflation and deflation processes. The aim of this study was to relate ventilation-induced changes in lung density distribution, as measured over several respiratory cycles by dCT, to oxygenation and shunt fraction in a lavage acute respiratory distress syndrome model. METHODS: Six anaesthetized pigs underwent pressure-constant ventilation (FIO2=1.0, inspiratory:expiratory ratio=1:1) before and after induction of lung damage by saline lavage. Mean airway pressure (Paw) was varied (8, 13, 18, 23, 28, 33, and 38 cm H2O) in random order. At each Paw level, dCT acquisitions were performed over several respiratory cycles (Somatom Plus4, Siemens; supradiaphragmatic transverse slice; thickness=1 mm; temporal resolution=100 ms). During scanning at each Paw, arterial and mixed venous blood were obtained for blood gas analysis and shunt calculation. In each CT image, fractional areas (FA) of defined density ranges representing ventilated lung and atelectasis were determined by planimetry using dedicated software. The FA data of individual 100 ms scans were averaged over several respiratory cycles, and expressed as mean FA in percentage of total lung area at each Paw. For atelectatic lung parenchyma a quantitative relationship of the respective mean FA to shunt fraction was studied using regression analysis. RESULTS: Under steady-state conditions, mean FA of atelectasis correlated linearly with the calculated shunt fraction (healthy lungs, r=+0.76; lavaged lungs, r=+0.89). There is a non-linear relationship between mean FA of ventilated lung parenchyma and mean FA of atelectasis with PaO2. CONCLUSIONS: We conclude that dCT allows assessment of the effects of ventilator adjustments and resultant Paw; changes upon lung aeration and oxygenation rapidly, and with good spatial and temporal resolution. This may benefit patients with acute lung injury, whose ventilatory pattern may be optimized as early as during their first diagnostic workup.

Animals↗

PubMed2003

Improved artificial neural networks in prediction of malignancy of lesions in contrast-enhanced MR-mammography.

The aim of this study was to evaluate the capability of improved artificial neural networks (ANN) and additional novel training methods in distinguishing between benign and malignant breast lesions in contrast-enhanced magnetic resonance-mammography (MRM). A total of 604 histologically proven cases of contrast-enhanced lesions of the female breast at MRI were analyzed. Morphological, dynamic and clinical parameters were collected and stored in a database. The data set was divided into several groups using random or experimental methods [Training & Testing (T&T) algorithm] to train and test different ANNs. An additional novel computer program for input variable selection was applied. Sensitivity and specificity were calculated and compared with a statistical method and an expert radiologist. After optimization of the distribution of cases among the training and testing sets by the T & T algorithm and the reduction of input variables by the Input Selection procedure a highly sophisticated ANN achieved a sensitivity of 93.6% and a specificity of 91.9% in predicting malignancy of lesions within an independent prediction sample set. The best statistical method reached a sensitivity of 90.5% and a specificity of 68.9%. An expert radiologist performed better than the statistical method but worse than the ANN (sensitivity 92.1%, specificity 85.6%). Features extracted out of dynamic contrast-enhanced MRM and additional clinical data can be successfully analyzed by advanced ANNs. The quality of the resulting network strongly depends on the training methods, which are improved by the use of novel training tools. The best results of an improved ANN outperform expert radiologists.

Algorithms↗