Biomedical subjects

Christian Klessen

Publications and source records attributed to Christian Klessen.

9 recordsLinked to original sources

PubMed2006

Local staging of rectal cancer: the current role of MRI.

With the advent of powerful gradient coil systems and high-resolution surface coils, magnetic resonance imaging (MRI) has recently extended its role in the staging of rectal cancer. MRI is superior to endorectal ultrasound, the most widely used staging modality in patients with rectal tumors, in that it visualizes not only the intestinal wall but also the surrounding pelvic anatomy. The crucial advantage of MRI is not that it enables exact T-staging but precise evaluation of the topographic relationship of a tumor to the mesorectal fascia. This fascia is the most important anatomic landmark for the feasibility of total mesorectal excision, which has evolved into the standard operative procedure for the resection of cancer located in the middle or lower third of the rectum. MRI is currently the only imaging modality that is highly accurate in predicting whether or not it is likely that a tumor-free margin can be achieved and thus provides important information for planning of an effective therapeutic strategy, especially in patients with advanced rectal cancer.

Contrast Media↗

PubMed2006

Acute myocardial ischemia after aortic valve replacement: a comprehensive diagnostic evaluation using dynamic multislice spiral computed tomography.

We describe the case of a 72-year-old man presenting with endocarditis and clinical signs of acute myocardial ischemia after biological aortic valve replacement. A comprehensive cardiac dynamic multislice spiral computed tomography demonstrated: (1) an endocarditic vegetation of the aortic valve; (2) a subvalvular leakage feeding a paravalvular pseudoaneurysm based on an aortic root abscess with subsequent compromise of the systolic blood flow in the left main coronary artery and the resulting myocardial perfusion deficit.

Aged↗

PubMed2006

Pictorial review: electron beam computed tomography and multislice spiral computed tomography for cardiac imaging.

Electron beam computed tomography (EBCT) revolutionized cardiac imaging by combining a constant high temporal resolution with prospective ECG triggering. For years, EBCT was the primary technique for some non-invasive diagnostic cardiac procedures such as calcium scoring and non-invasive angiography of the coronary arteries. Multislice spiral computed tomography (MSCT) on the other hand significantly advanced cardiac imaging through high volume coverage, improved spatial resolution and retrospective ECG gating. This pictorial review will illustrate the basic differences between both modalities with special emphasis to their image quality. Several experimental and clinical examples demonstrate the strengths and limitations of both imaging modalities in an intraindividual comparison for a broad range of diagnostic applications such as coronary artery calcium scoring, coronary angiography including stent visualization as well as functional assessment of the cardiac ventricles and valves. In general, our examples indicate that EBCT suffers from a number of shortcomings such as limited spatial resolution and a low contrast-to-noise ratio. Thus, EBCT should now only be used in selected cases where a constant high temporal resolution is a crucial issue, such as dynamic (cine) imaging. Due to isotropic submillimeter spatial resolution and retrospective data selection MSCT seems to be the non-invasive method of choice for cardiac imaging in general, and for assessment of the coronary arteries in particular. However, technical developments are still needed to further improve the temporal resolution in MSCT and to reduce the substantial radiation exposure.

Animals↗

PubMed2006

Respiratory-triggered MRCP applying parallel acquisition techniques.

PURPOSE: To evaluate the influence of parallel imaging on the image quality of respiratory triggered magnetic resonance cholangiopancreatography (MRCP). MATERIALS AND METHODS: A total of 30 consecutive patients underwent MRCP applying a respiratory triggered T2-weighted (T2w) turbo spin-echo (TSE) sequence without and with parallel imaging (acceleration factor of 2). Acquisition times of both sequences were recorded. Quantitative evaluation included measurement of a contour sharpness index of two segments of the pancreaticobiliary tree as well as calculation of the relative contrast between ductal structures and organ parenchyma at four different segments. The qualitative evaluation was performed by two independent radiologists who graded overall image quality, depiction of eight segments of the pancreaticobiliary tree, and the frequency of artifacts. RESULTS: The application of parallel imaging significantly (P<0.05) reduced the acquisition time of the respiratory triggered MRCP sequence by 37.7% (six minutes and two seconds+/-one minute and 26 seconds vs. three minutes and 46 seconds+/-58 seconds). The quantitative and qualitative evaluation revealed no statistically significant differences between the two sequences (P>0.05). The frequency of artifacts was at the same level for both sequences as well. CONCLUSION: The application of parallel imaging for respiratory triggered MRCP significantly reduces the acquisition time without relevant influence on image quality.

Adult↗

PubMed2005

Magnetic resonance cholangiopancreatography using a free-breathing T2-weighted turbo spin-echo sequence with navigator-triggered prospective acquisition correction.

PURPOSE: The objective of this study was to evaluate the image quality of a respiratory-triggered T2-weighted (T2w) turbo spin-echo (TSE) sequence for magnetic resonance cholangiopancreatography (MRCP) using a new method for respiratory triggering by tracking the motion of the right diaphragm [prospective acquisition correction (PACE) technique]. MATERIALS AND METHODS: Fifty consecutive patients underwent MRCP imaging applying breath-hold half-Fourier single-shot TSE sequences and the respiratory-triggered T2w TSE sequence. Qualitative evaluation grading the depiction of eight segments of the pancreaticobiliary tree and the frequency of artifacts was performed. Quantitative evaluation included calculation of the relative contrast (RC) between fluid-filled ductal structures and organ parenchyma at four segments. RESULTS: A significantly higher (P<.01) RC was measured for the respiratory-triggered T2w TSE sequence [maximum intensity projection (MIP)] for all of the four investigated segments (one of four segments for the MIP) of the pancreaticobiliary tree, as well as a significant (P<.01) improvement of visualization of all ductal segments compared with the breath-hold sequences. The frequency of artifacts was significantly lower (P<.01) compared with the breath-hold sequences. CONCLUSION: Respiratory-triggered MRCP using a T2w TSE sequence with PACE significantly improves image quality and may be included into the routine MRCP sequence protocol.

Adult↗

PubMed2005

Magnetic resonance imaging of the upper abdomen using a free-breathing T2-weighted turbo spin echo sequence with navigator triggered prospective acquisition correction.

PURPOSE: To evaluate a free-breathing navigator triggered T2-weighted turbo spin-echo sequence with prospective acquisition correction (T2w-PACE-TSE) for MRI of the upper abdomen in comparison to a conventional T2-weighted TSE (T2w-CTSE), a single-shot TSE (T2w-HASTE), and a T1-weighted gradient-echo sequence (T1w-FLASH). MATERIALS AND METHODS: A total of 40 consecutive patients were examined at 1.5 T using free-breathing T2w-PACE-TSE, free-breathing T2w-CTSE, and breath-hold T2w-HASTE and T1w-FLASH acquisition. Images were evaluated qualitatively by three radiologists regarding motion artifacts, liver-spleen contrast, depiction of intrahepatic vessels, the pancreas and the adrenal glands, and overall image quality on a four-point scale. Quantitative analysis of the liver-spleen contrast was performed. RESULTS: Depiction and sharpness of intrahepatic vessels were rated significantly better (P < 0.01) using T2w-PACE-TSE compared to T2w-CTSE and T2w-HASTE sequences. Significantly higher contrast values were measured for T2w-PACE-TSE images compared to T2w-CTSE, T2w-HASTE, and T1w-FLASH images (P < 0.01). Mean examination time of the T2w-PACE-TSE was 7.91 minutes, acquisition time of the T2w-CTSE sequence was 4.52 minutes. CONCLUSION: Prospective acquisition correction is an efficient method for reducing respiratory movement artifacts in T2w-TSE imaging of the upper abdomen. Compared to T2w-CTSE and T2w-HASTE sequences recognition of anatomical details and contrast can be significantly improved.

Abdomen↗

PubMed2005

Multislice computed tomography for preoperative evaluation of right ventricular volumes and function: comparison with magnetic resonance imaging.

BACKGROUND: This study was performed to validate preoperative right ventricular measurements obtained from multislice spiral computed tomography data sets in comparison with magnetic resonance imaging. METHODS: Before cardiac surgery, 25 patients (among them 12 patients with compromised right ventricular function) underwent contrast-enhanced retrospectively electrocardiogram-gated multislice spiral computed tomography and cine magnetic resonance imaging in a standardized fashion. Right ventricular end-diastolic, end-systolic and stroke volume, ejection fraction, and myocardial mass were calculated according to the slice summation method. Measurements obtained with both modalities were compared using Pearson's correlation coefficient (r), Student's t test for paired samples, and Bland-Altman analysis. RESULTS: The right ventricle was completely visualized with invariably adequate image quality on all multislice spiral computed tomography and magnetic resonance images. For all measurements a close correlation between multislice spiral computed tomography and magnetic resonance imaging was found (end-diastolic volume, r = 0.93; end-systolic volume, r = 0.95; stroke volume, r = 0.91; ejection fraction, r = 0.96; mass, r = 0.94). Mean values of all measurements did not differ significantly between both modalities, and limits of agreement were in an acceptable range. CONCLUSIONS: When compared with magnetic resonance imaging as a reference method, multislice spiral computed tomography seems to be an accurate and reliable noninvasive technique for evaluating right ventricular measurements.

Adult↗

PubMed2003

Regional differences and post-mortem stability of enzymatic activities in the retinal pigment epithelium.

BACKGROUND: The retinal pigment epithelium (RPE) is essential for the metabolism of the neural retina. As a result of dysfunction of the RPE, retinal degeneration occurs. A potential treatment for certain forms of retinal degenerations is transplantation of RPE cells. To determine optimal conditions for treatment of donor eyes before transplantation, activities of key proteases (aminopeptidase M, dipeptidylpeptidase II and IV and gamma-glutamyltranspeptidase) as indicators of RPE cell quality (viability and functional state) were measured. METHODS: Protease activities were quantified in bovine RPE cells from different regions of the eyecup, after different times of storage of the bulbi, cryopreservation of the RPE cells and in RPE cell cultures. The distribution of the activities was compared to the pigmentation of the RPE cells, the thickness of the choroid and photoreceptor density. RESULTS: Most proteases showed regional maxima. Prolonged storage of the bulbi decreased gamma-glutamyltranspeptidase and aminopeptidase M activities. Cryopreservation of the RPE cells for up to 6 weeks caused no loss in the enzymatic activities. Culture of RPE cells caused pronounced decreases in the activities of gamma-glutamyltranspeptidase and dipeptidylpeptidase IV. Storage of the bulbi at 4 degrees C for more than 50 h causes marked loss of enzymatic activities in RPE cells. CONCLUSION: The decrease in gamma-glutamyltranspeptidase activity may be especially important because the RPE is exposed to high concentrations of reactive oxygen species. Whole bulbi should be stored for less than 50 h, but isolated RPE cells may be stored at -80 degrees C for weeks. Propagation of RPE cells by culture increases cell number; this effect may be counteracted by a decrease in the function of these cells.

Animals↗

PubMed2003

Isolation of bovine retinal pigment epithelial cells using adhesion to agarose: demonstration of cellular and regional heterogeneity.

The retinal pigment epithelium (RPE) shows cell heterogeneity in morphology and enzymatic activity. Routine isolation procedures for RPE cells may reduce enzymatic activity and prevent the quantification of regional enzymatic differences in vivo. We developed a new technique for the isolation of RPE cells based on adhesion of the cells to agarose. The morphology of the isolated cells resembled that of RPE cells in vivo. The cells were viable in the dye exclusion test and showed a histochemical staining pattern as RPE cells in vivo. With this technique, quantitative regional differences in the enzymatic activities were detected.

Animals↗