Biomedical subjects

Lutz Lüdemann

Publications and source records attributed to Lutz Lüdemann.

8 recordsLinked to original sources

PubMed2006

Usage of the T1 effect of an iron oxide contrast agent in an animal model to quantify myocardial blood flow by MRI.

BACKGROUND: To present a new method for fully quantitative analysis of myocardial blood flow (MBF) using magnetic resonance imaging. The first pass of an intravascular iron oxide contrast medium can be used to quantify myocardial perfusion. The technique was validated in an animal model using colored microspheres. MATERIALS AND METHODS: In six pigs, a tracking catheter was positioned in the left anterior descending artery (LAD). Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was performed on a 1.5-T scanner using a hybrid gradient-echo/echoplanar imaging (GRE-EPI) sequence. Regional myocardial blood flow (rMBF) was altered by either inducing vasodilatation with adenosine or creating coronary artery obstruction. The T(1) effect of a superparamagnetic iron oxide-based contrast medium (Resovist) administered at a dose of 8 micromol/kg was used. Upslope, time-to-peak and peak intensity were calculated from the signal intensity-time curves and absolute rMBF using the Kety-Schmidt equation; results were compared to those obtained using colored microspheres. RESULTS: The mean rMBF calculated by MRI was 1.49 (+/-6.91, quartile width) ml/min/g versus 3.21 (+/-1.61) ml/min/g measured by means of microspheres under resting conditions. rMBF increased to a mean of 6.21 (+/-2.83) ml/min/g versus 4.22 (+/-1.70) ml/min/g under adenosine and was reduced to zero flow in total occlusion. Linear regression showed the best correlation for upslope (R=0.714), time-to-peak (R=0.626) and the Kety-Schmidt equation (R=0.584). CONCLUSIONS: The T(1) effect of an iron oxide-based contrast medium allows determination of rMBF when using the Kety-Schmidt equation. The results are similar to those obtained with the standard of reference, colored micropheres, but not better than the results of the semiquantitative approach.

Adenosine↗

PubMed2006

BOLD signal in the motor cortex shows a correlation with the blood volume of brain tumors.

PURPOSE: To investigate whether and how the blood-oxygenation-level-dependent (BOLD) functional MRI (fMRI) signal is modified by brain tumors. MATERIALS AND METHODS: The BOLD signal depends on the perfusion, which in turn may be affected in the presence of a tumor. Some studies have demonstrated a reduced BOLD signal in the tumor-bearing hemisphere. The BOLD signal variation in the motor cortex area was studied with finger tapping in a brain tumor group and a control group. An a priori volume-of-interest (VOI)-based method was applied that allows quantification of the mean BOLD signal amplitude and extent of activated volume. BOLD signal amplitude and activated volume were correlated with the extent of edema, a mass effect on the central sulcus, tumor volume, distance of tumor to somatosensory cortex, and tumor blood volume. RESULTS: In the tumor group the ipsilateral activated volume was reduced by 21% (P = 0.025) and the mean signal amplitude was reduced by 16% (P = 0.004). The mean BOLD signal amplitude shows a significant correlation with the total intratumoral blood volume (P = 0.014). CONCLUSION: We concluded that the peritumoral perfusion was reduced resulting due to a tumor aspirating perfusion (steal phenomenon).

Adolescent↗

PubMed2005

Quantitative measurement of leakage volume and permeability in gliomas, meningiomas and brain metastases with dynamic contrast-enhanced MRI.

The spatial properties and function of the tumor vasculature differ with the tumor type and grade. T1-weighted dynamic contrast-enhanced imaging technique enables the simultaneous quantification of some functional parameters of the vasculature. These are the fractional contrast-enhancing volumes of the tissue compartments (blood volume and leakage/extravascular extracellular volume) and the exchange parameters (perfusion and permeability). The relatively long monitoring duration of 12 min used here made it necessary to divide the extravascular extracellular compartment into two subcompartments, a slowly and a fast enhancing one with different permeabilities. Forty-one gliomas (WHO grades II-IV), six meningiomas and eight distant metastases were investigated. It was shown that the technique noninvasively provides information for separating different tumor types and characterizing their microenvironment. Fast permeability describes vessel permeability and was significantly increased in meningiomas as compared with intra-axial tumors. The corresponding volume of the fast enhancing compartment was significantly increased in meningiomas compared to all gliomas taken together. Slow permeability describes diffusion within the extravascular extracellular space and was significantly reduced in low-grade gliomas, indicating short diffusion distances. The slowly enhancing extravascular extracellular space was found to be increased in high-grade gliomas and distant metastases. Blood volume differed significantly among some tumor entities and glioma grades. Perfusion was shown to increase linearly with blood volume for volumes of up to 20%, flattening out thereafter. The scatter plots of extravascular extracellular volume and blood volume were shown to differ among the tumor entities.

Adolescent↗

PubMed2005

In vivo assessment of the tolerance dose of small liver volumes after single-fraction HDR irradiation.

PURPOSE: To prospectively assess a dose-response relationship for small volumes of liver parenchyma after single-fraction irradiation. METHODS AND MATERIALS: Twenty-five liver metastases were treated by computed tomography (CT)-guided interstitial brachytherapy. Magnetic resonance imaging was performed 1 day before and 3 days and 6, 12, and 24 weeks after therapy. MR sequences included T1-w gradient echo (GRE) enhanced by hepatocyte-targeted gadobenate dimeglumine. All MRI data sets were merged with 3D dosimetry data and evaluated by two radiologists. The reviewers indicated the border of hyperintensity on T2-w images (edema) or hypointensity on T1-w images (loss of hepatocyte function). Based on the total 3D data, a dose-volume histogram was calculated. We estimated the threshold dose for either edema or function loss as the D(90), i.e., the dose achieved in at least 90% of the pseudolesion volume. RESULTS: Between 3 days and 6 weeks, the extension of the edema increased significantly from the 12.9 Gy isosurface to 9.9 Gy (standard deviation [SD], 3.3 and 2.6). No significant change was detected between 6 and 12 weeks. After 24 weeks, the edematous tissue had shrunk significantly to 14.7 Gy (SD, 4.2). Three days postbrachytherapy, the D(90) for hepatocyte function loss reached the 14.9 Gy isosurface (SD, 3.9). At 6 weeks, the respective zone had increased significantly to 9.9 Gy (SD, 2.3). After 12 and 24 weeks, the dysfunction volume had decreased significantly to the 11.9 Gy and 15.2 Gy isosurface, respectively (SD, 3 and 4.1). CONCLUSIONS: The 95% interval from 7.6 to 12.2 Gy found as the minimal hepatocyte tolerance after 6 weeks accounts for the radiobiologic variations found in CT-guided brachytherapy, including heterogeneous dose rates by variable catheter arrays.

Adult↗

PubMed2005

Influence of high magnetic field strengths and parallel acquisition strategies on image quality in cardiac 2D CINE magnetic resonance imaging: comparison of 1.5 T vs. 3.0 T.

The aim of this paper is to examine signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and image quality of cardiac CINE imaging at 1.5 T and 3.0 T. Twenty volunteers underwent cardiac magnetic resonance imaging (MRI) examinations using a 1.5-T and a 3.0-T scanner. Three different sets of breath-held, electrocardiogram-gated (ECG) CINE imaging techniques were employed, including: (1) unaccelerated SSFP (steady state free precession), (2) accelerated SSFP imaging and (3) gradient-echo-based myocardial tagging. Two-dimensional CINE SSFP at 3.0 T revealed an SNR improvement of 103% and a CNR increase of 19% as compared to the results obtained at 1.5 T. The SNR reduction in accelerated 2D CINE SSFP imaging was larger at 1.5 T (37%) compared to 3.0 T (26%). The mean SNR and CNR increase at 3.0 T obtained for the tagging sequence was 88% and 187%, respectively. At 3.0 T, the duration of the saturation bands persisted throughout the entire cardiac cycle. For comparison, the saturation bands were significantly diminished at 1.5 T during end-diastole. For 2D CINE SSFP imaging, no significant difference in the left ventricular volumetry and in the overall image quality was obtained. For myocardial tagging, image quality was significantly improved at 3.0 T. The SNR reduction in accelerated SSFP imaging was overcompensated by the increase in the baseline SNR at 3.0 T and did not result in any image quality degradation. For cardiac tagging techniques, 3.0 T was highly beneficial, which holds the promise to improve its diagnostic value.

Adult↗

PubMed2005

Implementation of a rapid inversion-prepared dual-contrast gradient echo sequence for quantitative dynamic contrast-enhanced magnetic resonance imaging of the human prostate.

The first step in quantitative pharmacokinetic modeling is to determine the arterial input function (AIF) by deriving the contrast medium (CM) concentration from an appropriate imaging sequence by monitoring changes in either the amplitude or the phase signal of an accommodative artery. The bolus passage is best detected on T2- or T2*-weighted images, while extravasation is best assessed on T1-weighted images. Here, an imaging sequence is used that employs a parallel acquisition technique for the interleaved acquisition of an inversion-prepared T1-weighted image and a T1/T2*-mixed-weighted image for determination of the AIF. The sequence was applied in six patients with prostate cancer. A method is presented for quantifying the AIF derived from the signal intensity-time courses of both the T1/T2*-mixed-weighted and the T1-weighted image. Furthermore, in some patients the signal intensity-time course of the T1-weighted image exhibits flow-induced signal modulations. To reduce the effect of this flow-related signal enhancement the corresponding phase information was used. The sequence presented here has the potential to improve the quantification of the AIF at all time points and pharmacokinetic modeling of the CM dynamics of the prostate.

Algorithms↗

PubMed2004

Cerebral ischemia in aneurysmal subarachnoid hemorrhage: a correlative microdialysis-PET study.

BACKGROUND AND PURPOSE: Cerebral microdialysis (MD) is discussed as a technique for detection of cerebral ischemia in subarachnoid hemorrhage; however, clinical data on cerebral blood flow (CBF) are limited in these patients. The main objective of this study was to investigate whether pathological MD parameters reflect a reduced regional CBF (rCBF) determined by 15O-H2O PET. METHODS: Thirteen subarachnoid hemorrhage patients (age, 48.7+/-15.0 years; World Federation of Neurological Surgeons grade 1 to 5) were studied. Extracellular glucose, lactate, lactate/pyruvate (L/P) ratio, glutamate, and glycerol levels were analyzed hourly. rCBF was determined in the volume of interest of the MD catheter and all vascular territories. MD values were correlated to rCBF on the day of PET. Then, MD concentrations of asymptomatic versus ischemic phases (3-day medians) were analyzed. RESULTS: In symptomatic patients (n=10), rCBF was significantly lower compared with controls (n=3, P=0.048). Glutamate correlated best with rCBF (r=-0.66; P=0.014), followed by glycerol (r=-0.62; P=0.021). The L/P ratio was most sensitive (0.82) and specific (1.0) in indicating symptoms of ischemia, but only during longer periods of ischemia. CONCLUSIONS: rCBF correlates best with glutamate, followed by glycerol, whereas the L/P ratio is sensitive only after longer periods of ischemia. Clinically relevant regional metabolic derangements occur already above an rCBF of 20 mL x 100 g(-1).min(-1). Future research should focus on identifying alternative causes of metabolic derangement in subarachnoid hemorrhage patients and optimal treatment management in these patients.

Adult↗

PubMed2004

[BANG-polymer dosimetry in the proton therapy of eye neoplasms].

The use of polymer gel makes it possible to measure three-dimensional dose distributions of ionizing radiation. Phantoms with BANG-1 and BANG-3 gel were irradiated using a 68 MeV proton beam at the eye tumour therapy beam line of the Hahn Meitner Institute in Berlin. Up to twelve treatment fields could be applied to one gel phantom. The investigations consisted of mono-energetic Bragg curves, spread-out Bragg curves of circular fields (diameter 20 mm), and spread-out Bragg curves of patient fields. Magnetic resonance imaging was used to obtain the gel dose distributions. The results were compared to measurements of a water-phantom ionization chamber. The BANG polymer gels showed a significant quenching of Bragg peaks compared to ionization chamber measurements. The BANG-3 gel was found to be unsuitable for further investigations with 68 MeV protons. The use of BANG-1 allowed the verification of wedge slopes and irregular field forms. On the basis of our experience, polymer gels are well suited for quality assurance in proton therapy in principle.

Eye Neoplasms↗