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Biomedical subjects

M Cohnen

Publications and source records attributed to M Cohnen.

At least 19 recordsLinked to original sources
PubMed2006

Feasibility of ultra-low-dose multi-detector-row CT-colonography: detection of artificial endoluminal lesions in an in-vitro-model with optimization of image quality using a noise reduction filter algorithm.

PURPOSE: To assess the most favorable slice thickness in Multi-Detector-Row CT-colonography (MDCTC), and the feasibility of dose reduction in an in-vitro-setting as well as the possibility of optimization of image quality using a noise reduction filter algorithm. - MATERIALS AND METHODS: 18 artificial lesions with sizes from 1 to 8 mm were randomly positioned in two cleansed pig colons. At a "Somatom Plus 4 Volume Zoom", six scanning protocols using a slice collimation of 2.5, 1, and 1 mm with a reconstructed slice thickness of 3, 3, and 1.25 mm were performed with tube currents of 100, and 10 mAs, respectively. Using a non-commercial software, a non-linear Gaussian filter was used to minimize image noise. Image noise was assessed before and after application of the filtering process. Using a threshold of -750 HU, two blinded readers analyzed the virtual colonography in respect to lesion location, size, and shape. Artifacts were noted. An automated detection system was evaluated. - RESULTS: Using 10 mAs, a ten-fold dose reduction was achieved. After application of the mathematical filter, image noise was reduced by 45-80% for 100 mAs, and by 50-70% for 10 mAs scans. Only with a slice thickness of 1.25 mm, all lesions could be detected. The definition of lesion size and shape was more accurate with higher mAs. Only minor noise artifacts were noted on low-dose images. The automated polyp detector marked not more than 60% of artificial lesions. - CONCLUSION: MDCTC benefits from narrow slice collimation. In an in-vitro-model, a significant dose reduction is achievable with preservation of a high lesion detection rate. The noise reduction filter algorithm improved image quality substantially.

Algorithms↗
PubMed2006

High-resolution multipinhole single-photon-emission computed tomography in experimental and human arthritis.

OBJECTIVE: To image inflammatory arthritic lesions in experimental arthritis and in patients with arthritis, using a newly developed high-resolution multipinhole single-photon-emission computed tomography (MPH-SPECT) technique. METHODS: Six interleukin-1 receptor antagonist-deficient mice with arthritis of the front and back paws and 2 control BALB/c mice were imaged with MPH-SPECT and scored macroscopically for arthritis. SPECT imaging was performed with a conventional gamma camera upgraded with a pyramidal lead collimator affixed with MPH apertures. All images were reconstructed, and uptake in the paws was quantified in counts/weight and injected activity. To transfer the imaging technique to humans we examined the clinically dominant hand of 6 individuals (3 with established rheumatoid arthritis [RA], 1 with early RA, 1 with osteoarthritis, and 1 healthy control). RESULTS: MPH-SPECT images were high-resolution 3-dimensional tomographic images, which allowed exact localization and quantifiable observation of increased bone metabolism. MPH-SPECT counts of inflamed joints in mice correlated with macroscopic scoring and histologic joint analysis postmortem. In humans, MPH-SPECT images depicted a detailed visualization of tracer accumulation in bony structures of hand and finger joints, and were also capable of imaging increased bone metabolism that had appeared normal with other imaging modalities, e.g., magnetic resonance imaging. CONCLUSION: The MPH-SPECT technique represents a new diagnostic tool in the detection of bone pathology in small-animal arthritis research. Compared with macroscopic scoring, this new method provides a more objective and higher-precision quantifiable measurement of bone reaction, allowing visualization of inflammatory processes of the whole skeleton in vivo. These results suggest that MPH-SPECT may be useful as a diagnostic instrument for monitoring experimental arthritis, with further potential for use in human studies of RA.

Aged↗
PubMed2006

[Diagnostic imaging for connective tissue diseases].

Guidelines and diagnostic algorithms for the introduction of diagnostic procedures for connective tissue diseases have not yet been established and standardized. Diagnosis is often based on the patients's typical history, clinical symptoms and specific laboratory profiles. The use of diagnostic imaging procedures is relevant for differential diagnosis, for the assessment of disease activity and organ involvement, for defining the prognosis and monitoring responses to therapy and side effects. Experience with these techniques and diagnostic procedures, their application, indications and analysis represent the platform for rational and optimal diagnosis as well of defined therapy stratification.

Antiphospholipid Syndrome↗
PubMed2006

[Interactive thresholded volumetry of abdominal fat using breath-hold t1-weighted magnetic resonance imaging].

PURPOSE: Development of a feasible and reliable method for determining abdominal fat using breath-hold T1-weighted magnetic resonance imaging. MATERIALS AND METHODS: The high image contrast of T1-weighted gradient echo MR sequences makes it possible to differentiate between abdominal fat and non-fat tissue. To obtain a high signal-to-noise ratio, the measurements are usually performed using phased array surface coils. Inhomogeneity of the coil sensitivity leads to inhomogeneity of the image intensities. Therefore, to examine the volume of abdominal fat, an automatic algorithm for intensity correction must be implemented. The analysis of the image histogram results in a threshold to separate fat from other tissue. Automatic segmentation using this threshold results directly in the fat volumes. The separation of intraabdominal and subcutaneous fat is performed by interactive selection in a last step. RESULTS: The described correction of inhomogeneity allows for the segmentation of the images using a global threshold. The use of semiautomatic interactive volumetry makes the analysis more subjective. The variance of volumetry between observers was 4.6 %. The mean time for image analysis of a T1-weighted investigation lasted less than 6 minutes. CONCLUSION: The described method facilitates reliable determination of abdominal fat within a reasonable period of time. Using breath-hold MR sequences, the time of examination is less than 5 minutes per patient.

Abdomen↗
PubMed2006

1H-MR spectroscopy, magnetization transfer, and diffusion-weighted imaging in alcoholic and nonalcoholic patients with cirrhosis with hepatic encephalopathy.

PURPOSE: Mild swelling of astrocytes is proposed as a key event in the pathogenesis of hepatic encephalopathy. Proton MR spectroscopy ((1)H-MR spectroscopy), diffusion-weighted imaging (DWI), and magnetization transfer imaging were performed in patients with alcoholic and nonalcoholic liver cirrhosis and correlated with different clinical stages of hepatic encephalopathy to assess alterations in cerebral water metabolism in different subgroups of patients with cirrhosis. MATERIAL AND METHODS: Forty-five patients (26 alcoholics, 19 nonalcoholics [due to hepatitis C (n = 9), hemochromatosis (n = 2), primary chronic cholangitis (n = 2), hepatitis B (n = 1), Wilson disease (n = 1), cryptogenic cirrhosis (n = 4)]) and 18 controls underwent (1)H-MR spectroscopy, magnetization transfer imaging, and DWI of the basal ganglia and normally appearing occipital white matter (NAWM). N-acetylaspartate (NAA), choline (Cho), myo-inositol (mIns), and glutamine/glutamate (Glx) relative to creatine (Cr), the apparent diffusion coefficients (ADC), and the magnetization transfer ratios (MTR) were correlated to the neuropsychologic status, which was assessed by computerized psychometry and mental state grading, according to the West Haven criteria. RESULTS: Compared with controls, nonalcoholic subjects exhibited a gradual increase of Glx/Cr in the basal ganglia and NAWM; a decrease in mIns/Cr; a significant decrease of MTR in the thalamus, the putamen, the pallidum, and NAWM; and an increase in the ADC of the NAWM with increasing hepatic encephalopathy severity. In alcoholics, mIns/Cr of the basal ganglia and the NAWM, Cho/Cr of the basal ganglia, and MTR of all assessed regions were decreased. Glx/Cr of the basal ganglia and of the NAWM was increased, compared with that of controls; but no correlation to the clinical hepatic encephalopathy grading was found. ADC did not change significantly between the groups. CONCLUSIONS: Apart from a typical pattern of (1)H-MR spectroscopy alterations in hepatic encephalopathy, a gradual decrease in MTR and an increase of ADC was found correlating to clinical grading of hepatic encephalopathy in nonalcoholic patients with cirrhosis. In alcoholic patients with hepatic encephalopathy, there was no such correlation. Abnormalities detected by MR imaging may hint at different pathways of brain damage in alcohol-induced liver disease.

Diffusion Magnetic Resonance Imaging↗
PubMed2006

Radiation exposure of patients in comprehensive computed tomography of the head in acute stroke.

BACKGROUND AND PURPOSE: To assess patient radiation exposure in comprehensive stroke imaging using multidetector row CT (MDCT) combining standard CT of the head, cerebral perfusion (CTP), and CT angiography (CTA) studies. METHODS: Examination protocols for CT and CTA of cerebral and cervical vessels, as well as CTP were simulated using a Somatom Sensation Cardiac 64. Effective doses were derived from measurements with the use of lithium-fluoride thermoluminescent dosimeters (LiF-TLD) at several organ sites using an Alderson-Rando phantom. RESULTS: LiF-TLD measurements resulted in effective doses of 1.7 mSv for CT, 1.9 mSv for CTA of intracranial vessels, and 2.8 mSv for CTA of cervical vessels, respectively. Depending on examination parameters, effective doses varied between 1.1 and 5.0 mSv for cerebral CTP. For CTP, local doses in the area of the primary beam ranged between 114 and 444 mGy. CONCLUSIONS: Comprehensive stroke imaging may result in up to 9.5 mSv with possible local doses of 490 mGy. Although critical doses for organ damage (eg, cataract formation or hair loss) are not reached, physicians need to be aware of possible radiation induced sequelae particularly in repetitive examinations.

Acute Disease↗
PubMed2005

[Transjugular intrahepatic portosystemic stent shunt: indications and long-term outcome].

The transjugular intrahepatic portosystemic stent shunt has replaced surgical shunt procedures as the standard therapy for complications of portal hypertension such as refractory ascites and recurrent variceal bleeding. However, reinterventions due to TIPS stenosis are necessary in 25-50 %. Major complications are the manifestation or worsening of hepatic encephalopathy. Recent studies using PTFE covered stents have shown lower stenosis rates and a trend towards prolonged survival.

Ascites↗
PubMed2005

[Assessment of two different software solutions for the evaluation of CT colonography].

PURPOSE: To compare a commercial CT colonography software ("Colonography", Siemens, Forchheim) with a non-commercial post-processing system ("Colotux", Department of Informatics). MATERIAL AND METHODS: Identical data sets of 10 patients, who underwent an ultra-low-dose multi-detector CT colonography (ULD-MDCTC) (4x1 mm collimation, 8 mm pitch, 120 kVp, 10 mAs) were analyzed retrospectively. Assessment was performed using both software solutions by two resident radiologists, who did not have any experience with any colonography software tool before and who did not know the clinical symptoms of the patients or the results of the conventional colonoscopy. Both systems were analyzed using several subjective quality criteria including workflow, handling, image quality, endoluminal navigation and analysis of lesions with grading on a 5-point-scale. Results concerning polyps were compared between the two systems as well as with conventional colonoscopy. RESULTS: Both colonography systems detected the same number of polyps. Although both showed some advantages for single criteria, no relevant difference was noted in general for subjective assessment. The time for calculation of three dimensional interactive volumes was three times longer for "Colotux" compared to "Colonography." Linux-based "Colotux" showed a trend towards better subjective image quality and easier measurement of polyp size. An intuitive desktop and "Syngo"-workflow integration were advantages of "Colonography." CONCLUSION: The analysis of CT colonographies (4-detector-row-CT-scanner, ultra low dose technique, supine position) can adequately be achieved by both software solutions. There was no significant subjective or objective difference of quality between a "stand-alone" individual system and a commercial workflow-integrated solution. A relevant factor for decision between the two systems may be the difference in time needed for the 3D volume calculation, especially in institutes with a high frequency of examinations.

Aged↗
PubMed2005

[Differential diagnosis of focal liver lesions using contrast-enhanced MRI with SHU 555 A in comparison with unenhanced MRI and multidetector spiral-CT].

PURPOSE: To evaluate the ability of contrast-enhanced MRI with SHU 555 A to provide additional information for characterization of focal liver tumors compared with non-enhanced MRI and multislice spiral CT. MATERIALS AND METHODS: In a prospective manner the images of 45 patients who underwent multislice spiral CT, unenhanced MRI alone and unenhanced and SHU 555 A-enhanced MRI including dynamic imaging at a field strength of 1.0 T were analyzed in a blinded reading. The readers had to determine on a scale from 1 to 5 whether a tumor was benign or malignant. Furthermore, the readers had to give a definitive diagnosis for each lesion. A true cut needle biopsy served as gold standard against which all imaging procedures were compared. RESULTS: The sensitivity for differentiation malignant vs. benign lesion was 77 % with spiral CT, 72 % with unenhanced MRI and 94 % with SHU 555 A-enhanced MRI, respectively (p < 0.05). The specificity for spiral CT was 73 %, for unenhanced MRI 83 % and for contrast-enhanced MRI 83 %, respectively (n. s.). Compared with the histopathologic results, the correct diagnosis was made with spiral CT in 25/45 (56 %), unenhanced MRI in 16/45 (36 %) and contrast-enhanced MRI in 32/45 (71 %) of the patients (p < 0.05). For the subgroup of patients with liver cirrhosis, the correct diagnosis was established with spiral CT in 16/23 (70 %), unenhanced MRI in 9/23 (39 %) and contrast-enhanced MRI in 19/23 (83 %) of the patients (p < 0.05). CONCLUSION: Contrast-enhanced MRI with SHU 555 A has the ability to improve the differential diagnosis of focal liver tumors compared with unenhanced MRI and multislice spiral CT.

Biopsy, Needle↗
PubMed2004

Prediction of relapse after antithyroid drug therapy of Graves' disease: value of color Doppler sonography.

Opinions differ regarding the indications for antithyroid drugs, radioiodine and surgery in patients with Graves' disease because the likelihood of long-term remission after medical treatment cannot be predicted. The aim of this study was to assess the value of quantifying thyroid blood flow in an attempt to predict outcome following withdrawal of antithyroid drug therapy. Spectral Doppler recordings were obtained from the thyroid arteries in 24 patients with Graves' disease at the time of diagnosis. Thyroid blood flow levels measured at the time of diagnosis of Graves' disease were correlated with outcome following withdrawal of medical treatment (mean duration of treatment: 14 months). Clinical follow-up for at least 18 months (range: 18 - 39 months) after antithyroid drug withdrawal was possible in 13 patients (12 women). Mean peak systolic velocity and volume flow rate values as well as thyroid volume measured at the time of diagnosis were significantly higher (139 cm/s, SD 46; 195 ml/min, SD 170; 52 ml, SD 18) in patients who relapsed after drug treatment compared with patients in remission (71 cm/s, SD 27; 67 ml/min, SD 61; 25 ml, SD 13). The correlation between thyroid blood flow measurements and thyroid volume was high (r = 0.79 - 0.96). Recurrence of disease could be predicted with a sensitivity of 71 % and a specificity of 100 % based on thyroid blood flow measurements. This preliminary data suggest that quantification of thyroid blood flow by means of Doppler sonography might be a useful tool to predict the outcome of Graves' disease following withdrawal of medical treatment and could be helpful in finding the adequate kind of therapy.

Adult↗
PubMed2004

Disseminated microvascular pulmonary tumor cell embolism: a rare cause of fulminant pulmonary hypertension.

BACKGROUND: Disseminated pulmonary tumor embolization is a rare cause of pulmonary hypertension and is often diagnosed only after the patient has died. CASE REPORT: We report on a 41-year-old male who was admitted because of severe dyspnea and tachycardia. Contrast enhanced spiral computed tomography did neither establish pulmonary thromboembolism nor pulmonary metastasis. Right heart catheterization revealed severe pulmonary hypertension (pulmonary vascular resistance (PVR) 678 dyn x sec x cm(-5)). PVR did not respond to therapy with intravenous nitrate or inhaled iloprost in this critically ill patient. 2 days after admission, the patient died because of refractory right heart failure. Autopsy revealed microscopic pulmonary tumor embolism due to a metastasizing adenocarcinoma of the pancreas. CONCLUSION: Disseminated tumor cell embolism should be considered as a rare differential diagnosis in patients with refractory pulmonary hypertension.

Adenocarcinoma↗
PubMed2004

Exclusion of brain lesions: is MR contrast medium required after a negative fluid-attenuated inversion recovery sequence?

We hypothesized that in patients with negative fluid-attenuated inversion recovery (FLAIR) images T(2) weighted fast spin-echo (FSE) images and T(1) weighted spin-echo (SE) images before and after intravenous administration of gadolinium-based contrast medium display no pathology either. Thus, we assessed the negative predictive value of FLAIR images to rule out MR-detectable brain lesions. 1026 consecutive cranial MR examinations were reviewed. Routine MRI of the brain included T(1) weighted coronal imaging before and after administration of gadopentetate dimeglumine, axial T(2) weighted FSE and fast-FLAIR imaging. The FLAIR images were rated by two radiologists into categories of 0 (without pathologic changes) and 1 (with pathologic changes). Two other radiologists analysed the complete examination. In 284 MR examinations of the brain no abnormalities were found (28%). FLAIR-ratings were false-negative in four cases and false-positive in 30 cases. Sensitivity and specificity of the FLAIR sequence for MR-detectable brain lesions were 99.5% and 89.4%. The unselective application of gadolinium avoided one false-negative MR-reading and improved the sensitivity of the MR-examination from 99.5% to 99.6%. Positive and negative predictive values were 96.1% and 98.4%, respectively. The interobserver reliability was kappa=0.93 for the FLAIR-readers and 0.89 for the readers who rated the complete examination. In conclusion, negative FLAIR images provide a high negative predictive value for MR-detectable brain lesions. Thus, in patients with negative FLAIR images the unselective application of gadolinium seems to be unnecessary.

Adolescent↗
PubMed2003

Lack of portosystemic bacterial translocation in patients with liver cirrhosis after placement of transjugular shunt.

The purpose of this study was to clarify whether bacteria are transferred from the portal venous system into central venous blood during the placement of a transjugular portosystemic stent shunt (TIPSS). TIPSS was created in 30 consecutive cirrhotic patients for recurrent variceal bleeding ( n=12), refractory ascites ( n=16), or hepatorenal syndrome ( n=2). Microbiological analysis was performed prospectively on central venous blood before and on portal venous blood immediately after puncture of the portal vein. Twenty minutes after the placement of TIPSS, another sample of central venous blood was obtained. None of the first two sets of blood cultures showed bacterial growth, so that no bacterial transfer was seen at the time of TIPSS placement. Four of the third sets of blood samples showed skin and mouth flora, interpreted as iatrogenic contamination.

Adult↗
PubMed2003

[Predictive parameters of infectiologic complications in patients after TIPSS].

AIM: To define predictive parameters of a complicated clinical course after the TIPSS procedure. METHODS: Blood cultures were drawn prospectively in 41 patients from a central line and from the portal venous blood before stent placement as well as from the central line 20 min after intervention. C-reactive protein (CRP) (mg/dl) and white blood cell count (WBC,/microl) on the day of TIPSS-procedure (d0), the first (d1) and seven (d7) days after TIPSS were compared in patients with a complicated clinical course (spontaneous bacterial peritonitis,pneumonia,sepsis; group I) to patients without clinical complications (group II) RESULTS: Group I showed a significant increase in CRP (d0: 1.8+/-1.0; d1: 3.2+/-1.5; d7: 4.3+/-3.2), and white blood cell count (d0: 7700+/-2600; d1: 10800+/-2800; d7: 7500+/-1800) on the first day after TIPSS-procedure in comparison to group II (CRP: d0: 1.6+/-0.6; d1: 1.8+/-1.0; d7: 1.9+/-0.6. WBC: d0: 6900+/-1500; d1: 8000+/-1600; d7: 7600+/-1400). Microbiological analysis showed in 12% skin or oral flora in the last sample. CONCLUSIONS: The course of CRP and WBC-count during the first week after TIPSS procedure may indicate patients with a potential risk of a complicated clinical course.

Adult↗