Christian Wybranski

Detection and characterisation of focal liver lesions in colorectal carcinoma patients: comparison of diffusion-weighted and Gd-EOB-DTPA enhanced MR imaging

ObjectiveTo compare diffusion-weighted imaging (DWI) and Gd-EOB-DTPA-enhanced magnetic resonance (MR) imaging for the detection and characterisation of focal liver lesions (FLLs) in patients with colorectal carcinoma.MethodsSeventy-three patients underwent MR imaging including echoplanar DWI (MR-DWI) and dynamic (MR-Dyn) and hepatobiliary phase (MR-Late) Gd-EOB-DTPA-enhanced images. Two blinded readers independently reviewed 5 different image sets using a 5-point confidence scale. Accuracy was assessed by the area (Az) under the receiver operating characteristic curve, and sensitivity and specificity were calculated.ResultsA total of 332 FLLs were evaluated. Detection rates were significantly higher for MR-Late images (94.4% for benign and 100% for malignant lesions) compared with MR-DWI (78.3% and 97.5%) and MR-Dyn images (81.5% and 89.9%). Accuracy was 0.82, 0.76 and 0.89 for MR-DWI, MR-Dyn and MR-Late images while sensitivity was 0.98, 0.87 and 0.95, respectively. For characterisation of subcentimetre lesions sensitivity was highest for MR-DWI (0.92). Combined reading of unenhanced and contrast-enhanced images had an identical high accuracy of 0.98.ConclusionLate-phase Gd-EOB-DTPA-enhanced images were superior for the detection of FLLs, while DWIs were most valuable for the identification of particularly small metastases. Combined interpretation of unenhanced images resulted in precise characterisation of FLLs.

Quantitative in vivo assessment of radiation injury of the liver using Gd-EOB-DTPA enhanced MRI: tolerance dose of small liver volumes

BackroundHepatic radiation toxicity restricts irradiation of liver malignancies. Better knowledge of hepatic tolerance dose is favourable to gain higher safety and to optimize radiation regimes in radiotherapy of the liver. In this study we sought to determine the hepatic tolerance dose to small volume single fraction high dose rate irradiation.Materials and methods23 liver metastases were treated by CT-guided interstitial brachytherapy. MRI was performed 3 days, 6, 12 and 24 weeks after therapy. MR-sequences were conducted with T1-w GRE enhanced by hepatocyte-targeted Gd-EOB-DTPA. All MRI data sets were merged with 3D-dosimetry data. The reviewer indicated the border of hypointensity on T1-w images (loss of hepatocyte function) or hyperintensity on T2-w images (edema). Based on the volume data, a dose-volume-histogram was calculated. We estimated the threshold dose for edema or function loss as the D90, i.e. the dose achieved in at least 90% of the pseudolesion volume.ResultsAt six weeks post brachytherapy, the hepatocyte function loss reached its maximum extending to the former 9.4Gy isosurface in median (i.e., ≥9.4Gy dose exposure led to hepatocyte dysfunction). After 12 and 24 weeks, the dysfunctional volume had decreased significantly to a median of 11.4Gy and 14Gy isosurface, respectively, as a result of repair mechanisms. Development of edema was maximal at six weeks post brachytherapy (9.2Gy isosurface in median), and regeneration led to a decrease of the isosurface to a median of 11.3Gy between 6 and 12 weeks. The dose exposure leading to hepatocyte dysfunction was not significantly different from the dose provoking edema.ConclusionHepatic injury peaked 6 weeks after small volume irradiation. Ongoing repair was observed up to 6 months. Individual dose sensitivity may differ as demonstrated by a relatively high standard deviation of threshold values in our own as well as all other published data.

Value of diffusion weighted MR imaging as an early surrogate parameter for evaluation of tumor response to high-dose-rate brachytherapy of colorectal liver metastases

BackgroundTo assess the value of diffusion weighted imaging (DWI) as an early surrogate parameter for treatment response of colorectal liver metastases to image-guided single-fraction 192Ir-high-dose-rate brachytherapy (HDR-BT).MethodsThirty patients with a total of 43 metastases underwent CT- or MRI-guided HDR-BT. In 13 of these patients a total of 15 additional lesions were identified, which were not treated at the initial session and served for comparison. Magnetic resonance imaging (MRI) including breathhold echoplanar DWI sequences was performed prior to therapy (baseline MRI), 2 days after HDR-BT (early MRI) as well as after 3 months (follow-up MRI). Tumor volume (TV) and intratumoral apparent diffusion coefficient (ADC) were measured independently by two radiologists. Statistical analysis was performed using univariate comparison, ANOVA and paired t test as well as Pearsons correlation.ResultsAt early MRI no changes of TV and ADC were found for non-treated colorectal liver metastases. In contrast, mean TV of liver lesions treated with HDR-BT increased by 8.8% (p = 0.054) while mean tumor ADC decreased significantly by 11.4% (p < 0.001). At follow-up MRI mean TV of non-treated metastases increased by 50.8% (p = 0.027) without significant change of mean ADC values. In contrast, mean TV of treated lesions decreased by 47.0% (p = 0.026) while the mean ADC increased inversely by 28.6% compared to baseline values (p < 0.001; Pearsons correlation coefficient of r = -0.257; p < 0.001).ConclusionsDWI is a promising imaging biomarker for early prediction of tumor response in patients with colorectal liver metastases treated with HDR-BT, yet the optimal interval between therapy and early follow-up needs to be elucidated.

Magnetic resonance-guided freehand radiofrequency ablation of malignant liver lesions: a new simplified and time-efficient approach using an interactive open magnetic resonance scan platform and hepatocyte-specific contrast agent.

ObjectivesThe aims of this study were to develop magnetic resonance (MR)–guided freehand radiofrequency ablation (RFA) using a near-real-time interactive MR platform in an open 1.0-T MR scanner and to determine the feasibility and safety of this new approach in the clinical setting. MethodsThe study was performed using an open 1.0-T MR system and a low-pass filter to prevent interaction between the RFA generator and the scanner. Artifact size of the radiofrequency needle was measured in 2 perpendicular views (transversal [tra] and coronal [cor]) in vitro and in the tra orientation in vivo for diagnostic (T1 high resolution isotropic volume excitation [THRIVE]/T2 turbo spin-echo [TSE]) and near-real-time (T1 fast-field-echo [FFE]) imaging. A liver-specific contrast medium (gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid) was administered 20 minutes before the intervention to enhance lesion visibility. Visibility was rated and compared for both interventional and diagnostic imaging sequences using a 10-point grading scale. Intervention time and complications were recorded. ResultsThe mean diameter of needle artifact size for interventional T1 FFE was 17.4 ± 0.7 mm (tra) and 17.1 ± 1.1 mm (cor) in vitro and 15.2 ± 1.5 mm (tra) in vivo. Artifact size for diagnostic imaging was 12.5 ± 1.8 mm (tra) and 11.2 ± 1.4 mm (cor) in vitro and 10.5 ± 1.7 mm in vivo using THRIVE and 8.1 ± 2.4 mm (tra) and 10.8 ± 1.8 mm (cor) in vitro and 9.7 ± 2.0 mm (tra) in vivo using T2 TSE.A total of 57 patients with liver malignancies (mean tumor size, 17 ± 7 mm) underwent freehand MR-guided RFA. In all patients, the ablative procedure was technically successful. Lesion visibility of the diagnostic T2 TSE sequence (4 ± 2) was significantly decreased compared with both the diagnostic (THRIVE, 7 ± 2) and interventional (T1 FFE, 8 ± 1) T1-weighted sequences. Mean time to position the applicator was 7.5 ± 2 minutes. Procedure times ranged from 30 to 60 minutes. The mean in-room time was 57 ± 22 minutes. No major complications were recorded. ConclusionsMagnetic resonance–guided freehand RFA using a near-real-time interactive MR platform in an open 1.0-T MR scanner is feasible, safe, and applicable in clinical routine. The administration of a hepatocyte-specific contrast agent enhances lesion visualization and therefore improves targeting. Without the need for additional sophisticated devices, this new approach simplifies and shortens the RFA procedure compared with previously published methods.

In Vivo Assessment of Dose Volume and Dose Gradient Effects on the Tolerance Dose of Small Liver Volumes after Single-Fraction High-Dose-Rate 192Ir Irradiation

Abstract The aim of this study was to assess the dependence of the normal liver tissue threshold dose on the volume exposed and the catheter geometry-dependent dose gradients for single-fraction high-dose-rate brachytherapy of malignant liver lesions. A total of 50 patients with malignant liver tumors treated with CT-guided high-dose-rate 192Ir brachytherapy were included. Dose planning was performed using a three-dimensional CT data set acquired after percutaneous applicator positioning. Magnetic resonance imaging (MRI), performed 6 and 12 weeks after therapy, was analyzed retrospectively. All MRI data sets were merged with 3D dosimetry data. The border of hyperintensity on T2-weighted images (edema) and of hypointensity on T1-weighted images (impaired hepatocyte function) were analyzed to assess the radiation effect. The threshold isodose surface of the volume exposed was calculated from the 3D dosimetry data. The relationships between irradiated volume and threshold isodose surface as well as dose gradient and threshold isodose surface were evaluated over time. The median threshold dose of the volume exposed, characterized by hepatocyte dysfunction and edema, was ≈13 Gy 6 weeks after irradiation and ≈16 Gy at 12 weeks. We found a significant correlation between the normal liver tissue threshold dose and volume exposed (P < 0.0001). The 12-week threshold dose was estimated between ≈14 Gy for 500 cm3, ≈16 Gy for 100 cm3, and ≈18 Gy for 10 cm3 of irradiated volume. The results indicate that the dose gradient has no effect on the threshold liver dose. There was a significant shift of the threshold doses from regions of lower to regions of higher-dose exposure in the course of follow-up (P < 0.0001). Thus the normal liver tissue threshold dose is dependent on the volume exposed but not on the dose gradient.

Nonrigid 3D Medical Image Registration and Fusion Based on Deformable Models

For coregistration of medical images, rigid methods often fail to provide enough freedom, while reliable elastic methods are available clinically for special applications only. The number of degrees of freedom of elastic models must be reduced for use in the clinical setting to archive a reliable result. We propose a novel geometry-based method of nonrigid 3D medical image registration and fusion. The proposed method uses a 3D surface-based deformable model as guidance. In our twofold approach, the deformable mesh from one of the images is first applied to the boundary of the object to be registered. Thereafter, the non-rigid volume deformation vector field needed for registration and fusion inside of the region of interest (ROI) described by the active surface is inferred from the displacement of the surface mesh points. The method was validated using clinical images of a quasirigid organ (kidney) and of an elastic organ (liver). The reduction in standard deviation of the image intensity difference between reference image and model was used as a measure of performance. Landmarks placed at vessel bifurcations in the liver were used as a gold standard for evaluating registration results for the elastic liver. Our registration method was compared with affine registration using mutual information applied to the quasi-rigid kidney. The new method achieved 15.11% better quality with a high confidence level of 99% for rigid registration. However, when applied to the quasi-elastic liver, the method has an averaged landmark dislocation of 4.32 mm. In contrast, affine registration of extracted livers yields a significantly (P = 0.000001) smaller dislocation of 3.26 mm. In conclusion, our validation shows that the novel approach is applicable in cases where internal deformation is not crucial, but it has limitations in cases where internal displacement must also be taken into account.

Thoracic-abdominal imaging with a novel dual-layer spectral detector CT: intra-individual comparison of image quality and radiation dose with 128-row single-energy acquisition

Background A novel, multi-energy, dual-layer spectral detector computed tomography (SDCT) is commercially available now with the vendor’s claim that it yields the same or better quality of polychromatic, conventional CT images like modern single-energy CT scanners without any radiation dose penalty. Purpose To intra-individually compare the quality of conventional polychromatic CT images acquired with a dual-layer spectral detector (SDCT) and the latest generation 128-row single-energy-detector (CT128) from the same manufacturer. Material and Methods Fifty patients underwent portal-venous phase, thoracic-abdominal CT scans with the SDCT and prior CT128 imaging. The SDCT scanning protocol was adapted to yield a similar estimated dose length product (DLP) as the CT128. Patient dose optimization by automatic tube current modulation and CT image reconstruction with a state-of-the-art iterative algorithm were identical on both scanners. CT image contrast-to-noise ratio (CNR) was compared between the SDCT and CT128 in different anatomic structures. Image quality and noise were assessed independently by two readers with 5-point-Likert-scales. Volume CT dose index (CTDIvol), and DLP were recorded and normalized to 68 cm acquisition length (DLP68). Results The SDCT yielded higher mean CNR values of 30.0% ± 2.0% (26.4–32.5%) in all anatomic structures (P < 0.001) and excellent scores for qualitative parameters surpassing the CT128 (all P < 0.0001) with substantial inter-rater agreement (κ ≥ 0.801). Despite adapted scan protocols the SDCT yielded lower values for CTDIvol (–10.1 ± 12.8%), DLP (−13.1 ± 13.9%), and DLP68 (–15.3 ± 16.9%) than the CT128 (all P < 0.0001). Conclusion The SDCT scanner yielded better CT image quality compared to the CT128 and lower radiation dose parameters.

In vivo assessment of catheter positioning accuracy and prolonged irradiation time on liver tolerance dose after single-fraction 192Ir high-dose-rate brachytherapy

BackgroundTo assess brachytherapy catheter positioning accuracy and to evaluate the effects of prolonged irradiation time on the tolerance dose of normal liver parenchyma following single-fraction irradiation with 192 Ir.Materials and methodsFifty patients with 76 malignant liver tumors treated by computed tomography (CT)-guided high-dose-rate brachytherapy (HDR-BT) were included in the study. The prescribed radiation dose was delivered by 1 - 11 catheters with exposure times in the range of 844 - 4432 seconds. Magnetic resonance imaging (MRI) datasets for assessing irradiation effects on normal liver tissue, edema, and hepatocyte dysfunction, obtained 6 and 12 weeks after HDR-BT, were merged with 3D dosimetry data. The isodose of the treatment plan covering the same volume as the irradiation effect was taken as a surrogate for the liver tissue tolerance dose. Catheter positioning accuracy was assessed by calculating the shift between the 3D center coordinates of the irradiation effect volume and the tolerance dose volume for 38 irradiation effects in 30 patients induced by catheters implanted in nearly parallel arrangement. Effects of prolonged irradiation were assessed in areas where the irradiation effect volume and tolerance dose volume did not overlap (mismatch areas) by using a catheter contribution index. This index was calculated for 48 irradiation effects induced by at least two catheters in 44 patients.ResultsPositioning accuracy of the brachytherapy catheters was 5-6 mm. The orthogonal and axial shifts between the center coordinates of the irradiation effect volume and the tolerance dose volume in relation to the direction vector of catheter implantation were highly correlated and in first approximation identically in the T1-w and T2-w MRI sequences (p = 0.003 and p < 0.001, respectively), as were the shifts between 6 and 12 weeks examinations (p = 0.001 and p = 0.004, respectively). There was a significant shift of the irradiation effect towards the catheter entry site compared with the planned dose distribution (p < 0.005). Prolonged treatment time increases the normal tissue tolerance dose. Here, the catheter contribution indices indicated a lower tolerance dose of the liver parenchyma in areas with prolonged irradiation (p < 0.005).ConclusionsPositioning accuracy of brachytherapy catheters is sufficient for clinical practice. Reduced tolerance dose in areas exposed to prolonged irradiation is contradictory to results published in the current literature. Effects of prolonged dose administration on the liver tolerance dose for treatment times of up to 60 minutes per HDR-BT session are not pronounced compared to effects of positioning accuracy of the brachytherapy catheters and are therefore of minor importance in treatment planning.

Minimally invasive tumor ablation in the liver

Image guided minimally invasive local and locoregional tumor ablation techniques like radiofrequency ablation, interstitial brachytherapy, transarterial chemoembolization (TACE) and selective internal radiotherapy (SIRT) with (90)Yttrium ( (90)Y) microspheres have been established as valuable amendments in oncologic therapy concepts. These techniques allow the destruction of extensive liver tumors with an acceptable toxicity profile. Necessity for a safe performance of these procedures is a close collaboration between interventional radiologist and anesthetist.

Accuracy of applicator tip reconstruction in MRI-guided interstitial 192Ir-high-dose-rate brachytherapy of liver tumors.

BACKGROUND AND PURPOSE To evaluate the reconstruction accuracy of brachytherapy (BT) applicators tips in vitro and in vivo in MRI-guided (192)Ir-high-dose-rate (HDR)-BT of inoperable liver tumors. MATERIALS AND METHODS Reconstruction accuracy of plastic BT applicators, visualized by nitinol inserts, was assessed in MRI phantom measurements and in MRI (192)Ir-HDR-BT treatment planning datasets of 45 patients employing CT co-registration and vector decomposition. Conspicuity, short-term dislocation, and reconstruction errors were assessed in the clinical data. The clinical effect of applicator reconstruction accuracy was determined in follow-up MRI data. RESULTS Applicator reconstruction accuracy was 1.6±0.5 mm in the phantom measurements. In the clinical MRI datasets applicator conspicuity was rated good/optimal in ⩾72% of cases. 16/129 applicators showed not time dependent deviation in between MRI/CT acquisition (p>0.1). Reconstruction accuracy was 5.5±2.8 mm, and the average image co-registration error was 3.1±0.9 mm. Vector decomposition revealed no preferred direction of reconstruction errors. In the follow-up data deviation of planned dose distribution and irradiation effect was 6.9±3.3 mm matching the mean co-registration error (6.5±2.5 mm; p>0.1). CONCLUSION Applicator reconstruction accuracy in vitro conforms to AAPM TG 56 standard. Nitinol-inserts are feasible for applicator visualization and yield good conspicuity in MRI treatment planning data. No preferred direction of reconstruction errors were found in vivo.