Markus Oechsner

A multi-institution evaluation of deformable image registration algorithms for automatic organ delineation in adaptive head and neck radiotherapy

BackgroundAdaptive Radiotherapy aims to identify anatomical deviations during a radiotherapy course and modify the treatment plan to maintain treatment objectives. This requires regions of interest (ROIs) to be defined using the most recent imaging data. This study investigates the clinical utility of using deformable image registration (DIR) to automatically propagate ROIs.MethodsTarget (GTV) and organ-at-risk (OAR) ROIs were non-rigidly propagated from a planning CT scan to a per-treatment CT scan for 22 patients. Propagated ROIs were quantitatively compared with expert physician-drawn ROIs on the per-treatment scan using Dice scores and mean slicewise Hausdorff distances, and center of mass distances for GTVs. The propagated ROIs were qualitatively examined by experts and scored based on their clinical utility.ResultsGood agreement between the DIR-propagated ROIs and expert-drawn ROIs was observed based on the metrics used. 94% of all ROIs generated using DIR were scored as being clinically useful, requiring minimal or no edits. However, 27% (12/44) of the GTVs required major edits.ConclusionDIR was successfully used on 22 patients to propagate target and OAR structures for ART with good anatomical agreement for OARs. It is recommended that propagated target structures be thoroughly reviewed by the treating physician.

Lung imaging under free-breathing conditions.

Respiratory motion and pulsatile blood flow can generate artifacts in morphological and functional lung imaging. Total acquisition time, and thus the achievable signal to noise ratio, is limited when performing breath‐hold and/or electrocardiogram‐triggered imaging. To overcome these limitations, imaging during free respiration can be performed using respiratory gating/triggering devices or navigator echoes. However, these techniques provide only poor gating resolution and can induce saturation bands and signal fluctuations into the lung volume. In this work, acquisition schemes for nonphase encoded navigator echoes were implemented into different sequences for morphological and functional lung imaging at 1.5 Tesla (T) and 0.2T. The navigator echoes allow monitoring of respiratory motion and provide an ECG‐trigger signal for correction of the heart cycle without influencing the imaged slices. Artifact free images acquired during free respiration using a 3D GE, 2D multislice TSE or multi‐Gradient Echo sequence for oxygen‐enhanced T  2* quantification are presented. Magn Reson Med, 2009.

Quantitative contrast-enhanced perfusion measurements of the human lung using the prebolus approach.

To investigate dynamic contrast‐enhanced MRI (DCE‐MRI) for quantification of pulmonary blood flow (PBF) and blood volume (PBV) using the prebolus approach and to compare the results to the global lung perfusion (GLP).

Dynamic Contrast-Enhanced MR Imaging for Differentiation of Rounded Atelectasis From Neoplasm

To characterize rounded atelectasis (RA) with dynamic contrast‐enhanced MRI in the differential diagnosis of solitary peripheral pulmonary neoplasm.

Sauerstoffverstärkte funktionelle MR-Lungenbildgebung

Current diagnostic tools for the assessment of lung function are limited by global measurements or the need for radioactive tracers. Ideally, these tools should allow quantitative, regional distinct analyses without exposure to radiation. The current paper presents oxygen-enhanced functional MRI for assessment of lung ventilation. First applied in humans in 1996, a considerable amount of experience is now available on 1.5T scanners. The generation of quantitative T1-maps shows a high clinical potential. Low-field MR scanners, which are mostly open-designed, are especially interesting for functional lung imaging. The open design has advantages in respect to patient comfort by lower noise production and easy access to the patients and the costs are lower (no need for helium cooling). Lower signal-to-noise ratios can be overcome by changing the relaxation times. New navigator techniques allow further compensations. This article focuses on the presentation of low-field scanners and the application of T1 and T2(*) maps is described for healthy volunteers and first patients.ZusammenfassungHeutige Verfahren zur Lungenfunktionsuntersuchung erlauben nur globale Analysen oder sind auf die Anwendung radioaktiver Tracer angewiesen. Wünschenswert wären jedoch quantitative, regional aufgelöste Techniken ohne jegliche Strahlenexposition. Der vorliegende Artikel stellt die sauerstoffverstärkte MR-Lungenfunktionsventilationsmessung vor. Erstmalig 1996 am Menschen eingesetzt, liegen bereits zahlreiche Erfahrungen mit 1,5-Tesla-Systemen vor. Dabei erwies sich insbesondere die quantitative T1-Bildgebung als zukunftsfähiges Verfahren. Besonders attraktiv für die funktionelle Lungenbildgebung sind so genannte offene Niederfeld-MR-Systeme. Vorteile sind die Patientenfreundlichkeit des Systems, insbesondere für die Untersuchung von Kindern und Jugendlichen, niedrige Kosten durch Verzicht auf Heliumkühlung und die deutlich geringere Geräuschentwicklung. Geringere Signal-zu-Rausch-Verhältnisse können durch veränderte Relaxationszeiten ausgeglichen werden. Neuere Navigationstechniken ermöglichen weitere Kompensationen. Der vorliegende Artikel fokussiert auf die Darstellung der Niederfeld-Lungen-MRT und stellt T1- wie auch T2*-Messungen an Probanden und ersten Patienten vor.AbstractCurrent diagnostic tools for the assessment of lung function are limited by global measurements or the need for radioactive tracers. Ideally, these tools should allow quantitative, regional distinct analyses without exposure to radiation. The current paper presents oxygen-enhanced functional MRI for assessment of lung ventilation. First applied in humans in 1996, a considerable amount of experience is now available on 1.5T scanners. The generation of quantitative T1-maps shows a high clinical potential. Low-field MR scanners, which are mostly open-designed, are especially interesting for functional lung imaging. The open design has advantages in respect to patient comfort by lower noise production and easy access to the patients and the costs are lower (no need for helium cooling). Lower signal-to-noise ratios can be overcome by changing the relaxation times. New navigator techniques allow further compensations. This article focuses on the presentation of low-field scanners and the application of T1 and T2* maps is described for healthy volunteers and first patients.

[Oxygen-enhanced functional MR lung imaging].

Current diagnostic tools for the assessment of lung function are limited by global measurements or the need for radioactive tracers. Ideally, these tools should allow quantitative, regional distinct analyses without exposure to radiation. The current paper presents oxygen-enhanced functional MRI for assessment of lung ventilation. First applied in humans in 1996, a considerable amount of experience is now available on 1.5T scanners. The generation of quantitative T1-maps shows a high clinical potential. Low-field MR scanners, which are mostly open-designed, are especially interesting for functional lung imaging. The open design has advantages in respect to patient comfort by lower noise production and easy access to the patients and the costs are lower (no need for helium cooling). Lower signal-to-noise ratios can be overcome by changing the relaxation times. New navigator techniques allow further compensations. This article focuses on the presentation of low-field scanners and the application of T1 and T2(*) maps is described for healthy volunteers and first patients.ZusammenfassungHeutige Verfahren zur Lungenfunktionsuntersuchung erlauben nur globale Analysen oder sind auf die Anwendung radioaktiver Tracer angewiesen. Wünschenswert wären jedoch quantitative, regional aufgelöste Techniken ohne jegliche Strahlenexposition. Der vorliegende Artikel stellt die sauerstoffverstärkte MR-Lungenfunktionsventilationsmessung vor. Erstmalig 1996 am Menschen eingesetzt, liegen bereits zahlreiche Erfahrungen mit 1,5-Tesla-Systemen vor. Dabei erwies sich insbesondere die quantitative T1-Bildgebung als zukunftsfähiges Verfahren. Besonders attraktiv für die funktionelle Lungenbildgebung sind so genannte offene Niederfeld-MR-Systeme. Vorteile sind die Patientenfreundlichkeit des Systems, insbesondere für die Untersuchung von Kindern und Jugendlichen, niedrige Kosten durch Verzicht auf Heliumkühlung und die deutlich geringere Geräuschentwicklung. Geringere Signal-zu-Rausch-Verhältnisse können durch veränderte Relaxationszeiten ausgeglichen werden. Neuere Navigationstechniken ermöglichen weitere Kompensationen. Der vorliegende Artikel fokussiert auf die Darstellung der Niederfeld-Lungen-MRT und stellt T1- wie auch T2*-Messungen an Probanden und ersten Patienten vor.AbstractCurrent diagnostic tools for the assessment of lung function are limited by global measurements or the need for radioactive tracers. Ideally, these tools should allow quantitative, regional distinct analyses without exposure to radiation. The current paper presents oxygen-enhanced functional MRI for assessment of lung ventilation. First applied in humans in 1996, a considerable amount of experience is now available on 1.5T scanners. The generation of quantitative T1-maps shows a high clinical potential. Low-field MR scanners, which are mostly open-designed, are especially interesting for functional lung imaging. The open design has advantages in respect to patient comfort by lower noise production and easy access to the patients and the costs are lower (no need for helium cooling). Lower signal-to-noise ratios can be overcome by changing the relaxation times. New navigator techniques allow further compensations. This article focuses on the presentation of low-field scanners and the application of T1 and T2* maps is described for healthy volunteers and first patients.

Dynamic Contrast-Enhanced Magnetic Resonance Imaging for Quantitative Lung Perfusion Imaging Using the Dual-Bolus Approach: Comparison of 3 Contrast Agents and Recommendation of Feasible Doses.

ObjectiveThe aims of this study were to compare 3 contrast agents and to define feasible doses for quantitative lung perfusion imaging using the dual-bolus approach in dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI). Materials and MethodsTen healthy volunteers (6 males, 4 females; mean age, 23.5 years) underwent DCE-MRI at 1.5 T using a 3D FLASH sequence. After a prebolus, 3 doses of gadopentetate dimeglumine (Gd-DTPA), gadofosveset, and gadobenate dimeglumine (Gd-BOPTA) were evaluated. Dose regimes were as follows: Gd-DTPA: 3.0 mL, 6.0 mL, and 12.0 mL with 1.5 mL prebolus; gadofosveset: 1.5 mL, 3.0 mL, and 6.0 mL with 0.8 mL prebolus; and Gd-BOPTA: 1.5 mL, 3.0 mL, and 6.0 mL with 0.8 mL prebolus. Pulmonary blood flow (PBF), pulmonary distribution volume, and mean transit time were assessed for each bolus. Region of interest measurements were used to determine the arterial input function (AIF) in the pulmonary trunk and signal intensities in lung parenchyma. Two radiologists independently rated the subjective image quality of the quantitative perfusion maps based on a 4-point Likert scale. ResultsDose-dependent signal saturation effects were observed for all 3 contrast agents concerning AIF and parenchyma measurements. Signal yields were comparable using Gd-BOPTA (AIF, 214.49 arbitrary units [AU]; parenchyma, 41.7 AU) and Gd-DTPA (207.43 AU; 36.3 AU). Gadofosveset showed significantly lower signal yield (165.74 AU; 25.2 AU; p < 0.008). Highest signal increase was observed for Gd-DTPA. Using Gd-DTPA, mean PBF values for the 3 doses (3 mL, 6 mL, 12 mL) in mL/min per milliliter lung volume were 2.9 ± 1.5, 2.4 ± 1.1, and 1.6 ± 1.0. For the 3 doses of gadofosveset (1.5 mL, 3 mL, 6 mL) mean PBF results were 3.1 ± 1.1, 1.9 ± 0.7, and 1.2 ± 0.6. Last, mean PBF values for Gd-BOPTA (1.5 mL, 3 mL, 6 mL) were 3.4 ± 1.7, 2.8 ± 1.3, and 2.0 ± 0.8. Measurements provided consistent values for all perfusion parameters (PBF, pulmonary distribution volume, mean transit time) when compared with reference literature. Contrast dose volume and the applied contrast agent had no relevant effects on the image quality scores. ConclusionsThe dual-bolus approach using a 3D FLASH sequence is a feasible tool for quantitative lung perfusion imaging. Small boluses of 3 mL for Gd-DTPA, 1.5 mL for Gd-BOPTA, and 1.5 mL for gadofosveset provide sufficient signal yield for quantitative parenchyma measurements. Using higher boluses falsely lower perfusion values have to be considered due to signal saturation effects. Although gadofosveset yielded the lowest signal, the generated quantitative perfusion maps were of diagnostic quality.

Evaluation of the tumor movement and the reproducibility of two different immobilization setups for image-guided stereotactic body radiotherapy of liver tumors

BackgroundThe purpose of this study is to evaluate the tumor movement and accuracy of patient immobilization in stereotactic body radiotherapy of liver tumors with low pressure foil or abdominal compression.MethodsFifty-four liver tumors treated with stereotactic body radiotherapy were included in this study. Forty patients were immobilized by a vacuum couch with low pressure foil, 14 patients by abdominal compression. We evaluated the ratio of gross tumor volume/internal target volume, the tumor movement in 4D-computed tomography scans and daily online adjustments after cone beam computed tomography scans.ResultsThe ratio of gross tumor volume/internal target volume was smaller with low pressure foil. The tumor movement in 4D-computed tomography scans was smaller with abdominal compression, the cranial movement even significantly different (p = 0.02). The mean online adjustments and their mean absolute values in the vertical, lateral and longitudinal axis were smaller with abdominal compression. The online adjustments were significantly different (p < 0.013), their absolute values in case of the longitudinal axis (p = 0.043). There was no significant difference of the adjustments’ 3D vectors.ConclusionsIn comparison to low pressure foil, abdominal compression leads to a reduction of the tumor movement. Online adjustments decreased significantly, thus leading to higher accuracy in patient positioning.

The Role of Navigated Transcranial Magnetic Stimulation Motor Mapping in Adjuvant Radiotherapy Planning in Patients With Supratentorial Brain Metastases

Purpose: In radiotherapy (RT) of brain tumors, the primary motor cortex is not regularly considered in target volume delineation, although decline in motor function is possible due to radiation. Non-invasive identification of motor-eloquent brain areas is currently mostly restricted to functional magnetic resonance imaging (fMRI), which has shown to lack precision for this purpose. Navigated transcranial magnetic stimulation (nTMS) is a novel tool to identify motor-eloquent brain areas. This study aims to integrate nTMS motor maps in RT planning and evaluates the influence on dosage modulations in patients harboring brain metastases. Materials and Methods: Preoperative nTMS motor maps of 30 patients diagnosed with motor-eloquent brain metastases were fused with conventional planning imaging and transferred to the RT planning software. RT plans of eleven patients were optimized by contouring nTMS motor maps as organs at risk (OARs). Dose modulation analyses were performed using dose-volume histogram (DVH) parameters. Results: By constraining the dose applied to the nTMS motor maps outside the planning target volume (PTV) to 15 Gy, the mean dose (Dmean) to the nTMS motor maps was significantly reduced by 18.1% from 23.0 Gy (16.9–30.4 Gy) to 18.9 Gy (13.5–28.8 Gy, p < 0.05). The Dmean of the PTV increased by 0.6 ± 0.3 Gy (1.7%). Conclusion: Implementing nTMS motor maps in standard RT planning is feasible in patients suffering from intracranial metastases. A significant reduction of the dose applied to the nTMS motor maps can be achieved without impairing treatment doses to the PTV. Thus, nTMS might provide a valuable tool for safer application of RT in patients harboring motor-eloquent brain metastases.

Sauerstoffverstärkte funktionelle MR-Lungenbildgebung@@@Oxygen-enhanced functional MR lung imaging

Current diagnostic tools for the assessment of lung function are limited by global measurements or the need for radioactive tracers. Ideally, these tools should allow quantitative, regional distinct analyses without exposure to radiation. The current paper presents oxygen-enhanced functional MRI for assessment of lung ventilation. First applied in humans in 1996, a considerable amount of experience is now available on 1.5T scanners. The generation of quantitative T1-maps shows a high clinical potential. Low-field MR scanners, which are mostly open-designed, are especially interesting for functional lung imaging. The open design has advantages in respect to patient comfort by lower noise production and easy access to the patients and the costs are lower (no need for helium cooling). Lower signal-to-noise ratios can be overcome by changing the relaxation times. New navigator techniques allow further compensations. This article focuses on the presentation of low-field scanners and the application of T1 and T2(*) maps is described for healthy volunteers and first patients.ZusammenfassungHeutige Verfahren zur Lungenfunktionsuntersuchung erlauben nur globale Analysen oder sind auf die Anwendung radioaktiver Tracer angewiesen. Wünschenswert wären jedoch quantitative, regional aufgelöste Techniken ohne jegliche Strahlenexposition. Der vorliegende Artikel stellt die sauerstoffverstärkte MR-Lungenfunktionsventilationsmessung vor. Erstmalig 1996 am Menschen eingesetzt, liegen bereits zahlreiche Erfahrungen mit 1,5-Tesla-Systemen vor. Dabei erwies sich insbesondere die quantitative T1-Bildgebung als zukunftsfähiges Verfahren. Besonders attraktiv für die funktionelle Lungenbildgebung sind so genannte offene Niederfeld-MR-Systeme. Vorteile sind die Patientenfreundlichkeit des Systems, insbesondere für die Untersuchung von Kindern und Jugendlichen, niedrige Kosten durch Verzicht auf Heliumkühlung und die deutlich geringere Geräuschentwicklung. Geringere Signal-zu-Rausch-Verhältnisse können durch veränderte Relaxationszeiten ausgeglichen werden. Neuere Navigationstechniken ermöglichen weitere Kompensationen. Der vorliegende Artikel fokussiert auf die Darstellung der Niederfeld-Lungen-MRT und stellt T1- wie auch T2*-Messungen an Probanden und ersten Patienten vor.AbstractCurrent diagnostic tools for the assessment of lung function are limited by global measurements or the need for radioactive tracers. Ideally, these tools should allow quantitative, regional distinct analyses without exposure to radiation. The current paper presents oxygen-enhanced functional MRI for assessment of lung ventilation. First applied in humans in 1996, a considerable amount of experience is now available on 1.5T scanners. The generation of quantitative T1-maps shows a high clinical potential. Low-field MR scanners, which are mostly open-designed, are especially interesting for functional lung imaging. The open design has advantages in respect to patient comfort by lower noise production and easy access to the patients and the costs are lower (no need for helium cooling). Lower signal-to-noise ratios can be overcome by changing the relaxation times. New navigator techniques allow further compensations. This article focuses on the presentation of low-field scanners and the application of T1 and T2* maps is described for healthy volunteers and first patients.