Hendrik Rathke

Comparison of four radiofrequency ablation systems at two target volumes in an ex vivo bovine liver model.

PURPOSE We aimed to validate actually achieved macroscopic ablation volumes in relation to calculated target volumes using four different radiofrequency ablation (RFA) systems operated with default settings and protocols for 3 cm and 5 cm target volumes in ex vivo bovine liver. MATERIALS AND METHODS Sixty-four cuboid liver specimens were ablated with four commercially available RFA systems (Radionics Cool-tip, AngioDynamic 1500X, Boston Scientific RF 3000, Celon CelonPower LAB): 16 specimens for each system; eight for 3 cm, and eight for 5 cm. Ablation diameters were measured, volumes were calculated, and RFA times were recorded. RESULTS For the 3 cm target ablation volume, all tested RFA systems exceeded the mathematically calculated volume of 14.14 cm3. For the 3 cm target ablation volume, mean ablation volume and mean ablation time for each RFA system were as follows: 28.5 ± 6.5 cm3, 12.0 ± 0.0 min for Radionics Cool-tip; 17.1 ± 4.9 cm3, 9.36 ± 0.63 min for AngioDynamic 1500X; 29.7 ± 11.7 cm3, 4.60 ± 0.50 min for Boston Scientific RF 3000; and 28.8 ± 7.0 cm3, 20.85 ± 0.86 min for Celon CelonPower LAB. For the 5 cm target ablation volume, Radionics Cool-tip (48.3 ± 9.9 cm3, 12.0 ± 0.0 min) and AngioDynamic 1500X (39.4 ± 16.2 cm3, 19.59 ± 1.13 min) did not reach the mathematically calculated target ablation volume (65.45 cm3), whereas Boston Scientific RF 3000 (71.8 ± 14.5 cm3, 9.15 ± 2.93 min) and Celon CelonPower LAB (93.9 ± 28.1 cm3, 40.21 ± 1.78 min) exceeded it. CONCLUSION While all systems reached the 3 cm target ablation volume, results were variable for the 5 cm target ablation volume. Only Boston Scientific RF 3000 and Celon CelonPower LAB created volumes above the target, whereas Radionics Cool-tip and AngioDynamic 1500X remained below the target volume. For the 3 cm target ablation volume, AngioDynamic 1500X with 21% deviation was closest to the target volume. For the 5 cm target volume Boston Scientific RF 3000 with 10% deviation was closest.

Non-invasive ECG-triggered 2D TOF MR angiography of the pelvic and leg arteries in an open 1.0-tesla high-field MRI system in comparison to conventional DSA

Abstract Objectives: A non-contrast-enhanced 2D time-of-flight magnetic resonance angiography (TOF-MRA) protocol was compared with the gold standard of planar digital subtraction angiography (DSA) by calculating correlations of vessel diameters. Methods: A total of 1134 vascular diameters in 81 corresponding sites were prospectively measured by TOF-MRA and DSA in seven patients (four women, three men; mean age, 68 years). For a total of 162 vascular segments per patient, 81 Spearman’s ρ correlation coefficients were calculated, consolidated to 41 due to consideration of symmetry (right/left), and assessed by correlation quality. Results: In the 41 consolidated segments, correlations were good, very good, and excellent in 25 segments (n=10>0.5, n=4>0.7, and n=11>0.8), moderate to poor in seven segments (n=4>0.3 and 0<n=3≤0.3), without in two, inverse in three, and nonmeasurable in four segments. Correlations were best for the main arteries above the knee, and these arteries were most consistently visualized. Conclusion: The TOF-MRA protocol presented here can be performed in an open 1.0-T MRI system in 60–90 min. Visualization is degraded when the target artery leaves the plane orthogonal to the imaging plane (1) or signal yield is poor due to small caliber (2).

Interactive near-real-time high-resolution imaging for MR-guided lumbar interventions using ZOOM imaging in an open 1.0 Tesla MRI system – initial experience

Abstract Purpose: Different techniques for magnetic resonance-guided lumbar interventions have been introduced in recent years. Appropriate pulse sequence design is crucial since high spatial resolution often comes at the cost of lower temporal resolution. The purpose of this study was to evaluate the value of accelerated reduced field of view (ZOOM)-based imaging sequences for lumbar interventions. Methods: ZOOM imaging was used in 31 interventions (periradicular, facet joint, epidural infiltrations, and discography) performed in 24 patients (10 women, 14 men; age 43±13.3 years). Signal-to-noise ratio and contrast-to-noise ratio (CNR) were determined and retrospectively compared with standard preinterventional (T2 weighted), peri-interventional (proton density), and postinterventional (spectral presaturation with inversion recovery [SPIR]) imaging. Needle artifacts were assessed by direct measurement as well as with parallel and perpendicular needle profiles. Puncture times were compared to similar interventions previously performed in our department. Results: No significant differences in signal intensities (standard/ZOOM: 152.0/151.6; p=0.136) and CNR values (2.0/4.0; p=0.487) were identified for T2-weighted sequences. The needle artifact signal intensity was comparable (648.1/747.5; p=0.172) for peri-interventional imaging. Standard interventional (fat needle: 43.8/23.4; p<0.001; muscle needle: 6.2/2.4; p<0.001) and SPIR sequences (43.3/13.9; p=0.010) showed a higher CNR than corresponding ZOOM sequences did. Needle artifacts were larger in ZOOM (2.4 mm/2.9 mm; p=0.005). The profiles revealed that ZOOM imaging delivers more overall signal intensity. The turning points of both profiles were comparable. ZOOM reduced intervention times significantly (329.1 s/228.5 s; p=0.026). Conclusion: ZOOM imaging is a feasible interactive sequence for lumbar interventions. It ameliorates the tradeoff between image quality and temporal resolution. Moreover, the sequence design reduces intervention times significantly.

Tailored interactive sequences for continuous MR-image-guided freehand biopsies of different organs in an open system at 1.0 tesla (T) – Initial experience

Abstract Objectives: To assess the feasibility, image quality, and accuracy of freehand biopsies of liver, bone, muscle, vertebral disc, soft tissue, and other lesions using balanced steady-state free precession (SSFP, balanced fast field echo: bFFE), spoiled and nonspoiled gradient echo (FFE), and turbo spin echo (TSE) sequences for interactive continuous navigation in an open magnetic resonance imaging (MRI) system at 1.0 tesla (T). Methods: Twenty-six MR-guided biopsies (five liver, five bone, four muscle, four vertebral disc, one lung, one kidney, one suprarenal gland, and five soft or other tissue) were performed in 23 patients in a 1.0-T open magnetic resonance (MR) scanner (Panorama HFO, Philips Healthcare, Best, the Netherlands). A total of 42 samples were obtained. Depending on lesion size and location, 14–18-gauge MR-compatible biopsy sets with a length of 100 or 200 mm (Somatex Medical, Teltow, Germany), 14–18-gauge MR-compatible semiautomatic biopsy guns with a length of 100 or 150 mm (Invivo, Schwerin, Germany), or 11-gauge MR-compatible bone marrow biopsy needles with a length of 100 mm (Somatex Medical, Teltow, Germany) were employed. Results: All lesions were visible with continuous interactive imaging. Our initial results indicate that bFFE is particularly suitable for fast-moving organs (pulmonary, paracardial); moving organs are targeted better with T1-weighted (T1W) TSE, T1W FFE (liver) or T2-weighted (T2W) TSE (complicated cysts, adrenal glands), and static organs are successfully approached with proton density (PD) (spine) or T1W TSE (peripheral bones, musculoskeletal system). No adverse events related to the use of MRI were obtained. No complications occurred according to the Society of Interventional Radiology (SIR) clinical practice guidelines. Conclusion: Applying tailored interactive dynamic imaging sequences for continuous navigation to liver, bone, muscle, vertebral disc, soft tissue, and other lesions can improve the feasibility, image quality, and interventional accuracy of freehand MR-guided biopsies and may hence reduce the risk of complications.

Initial experience with imaging of the lower extremity arteries in an open 1.0 Tesla MRI system using the triggered angiography non-contrast-enhanced sequence (TRANCE) compared to digital subtraction angiography (DSA).

Abstract Purpose: The aim of this study was to evaluate the feasibility and validity of arterial lower limb imaging with triggered angiography non-contrast enhanced (TRANCE) in an open MRI at 1.0 Tesla (T) compared to digital subtraction angiography (DSA). Material and methods: ECG-gated, non-contrast-enhanced magnetic resonance angiography (MRA) was performed in a 1.0-T high-field open magnetic resonance imaging (MRI) system which generates a vertical magnetic field. Three acquisition levels were defined (abdominal and pelvic level, arterial segments above the knee and segments below the knee) and a total of 1782 vessel diameter measurements were taken on a total of 11 patients with suspected peripheral arterial occlusive disease (PAOD) (8 men, 3 women; average age 66 years). In each patient, 162 vessel segments (81 each with TRANCE and DSA) were defined and measured. Pearson correlation coefficients were calculated. Results: At the abdominal/pelvic level, all mean values measured with DSA exceeded the mean values obtained with TRANCE. Above the knee, mean vessel diameters were measured smaller in DSA in six, equal in three, and larger in two vessel segments. Below the knee, all measured averages, except for the tibiofibular tract (TFT) measurements, were larger in TRANCE. In total, two small (≤0.3), two moderate (>0.3), 11 good (>0.5), 10 high (>0.7) and 13 very high (>0.8) correlations were obtained. Conclusions: Non-contrast-enhanced imaging of the lower limb arteries using a TRANCE-sequence in a 1.0 T open MRI system is feasible with the protocol presented; however, TRANCE tends to underestimate larger vessels and overestimate smaller vessels compared to DSA.

[Teleradiological report turnaround times: An internal efficiency and quality control analysis].

AIMS The teleradiological examinations performed at the Charité were analyzed for the purpose of internal quality and efficiency control. Data included the type and number of examinations performed, the time of day and week the examination was performed and the differences in teleradiologist report turnaround times. MATERIAL AND METHODS A retrospective analysis of the radiology information system (RIS) database of all teleradiological computed tomography examinations performed at the Charité from 2011 through 2013 was carried out. The search retrieved 10,200 teleradiological examinations which were included in the analysis. The records were analyzed for the time of the day and week the examination was performed, the interval between examination and time of reporting, the type of teleradiological examination and the campus in which they were performed. RESULTS The number of teleradiological examinations performed increased continuously during the observation period. Computed tomography of the head was the most frequently performed type of examination with 86%. Taking all forms of examination into consideration it took an average of 34 min until a report was written. Over the 3-year observation period the times remained virtually unaltered. CONCLUSION During the 3-year observation period nearly constant report times could be observed in spite of the increased numbers of examinations. This indicates an efficiency enhancement and rational integration of teleradiology into the radiological workflow.

Volume comparison of radiofrequency ablation at 3- and 5-cm target volumes for four different radiofrequency generators: MR volumetry in an open 1-T MRI system versus macroscopic measurement

Abstract Introduction: In a patient, it is usually not macroscopically possible to estimate the non-viable volume induced by radiofrequency ablation (RFA) after the procedure. The purpose of this study was to use an ex vivo bovine liver model to perform magnetic resonance (MR) volumetry of the visible tissue signal change induced by RFA and to correlate the MR measurement with the actual macroscopic volume measured in the dissected specimens. Materials and methods: Sixty-four liver specimens cut from 16 bovine livers were ablated under constant simulated, close physiological conditions with target volumes set to 14.14 ml (3-cm lesion) and 65.45 ml (5-cm lesion). Four commercially available radiofrequency (RF) systems were tested (n=16 for each system; n=8 for 3 cm and n=8 for 5 cm). A T1-weighted turbo spin echo (TSE) sequence with inversion recovery and a proton-density (PD)-weighted TSE sequence were acquired in a 1.0-T open magnetic resonance imaging (MRI) system. After manual dissection, actual macroscopic ablation diameters were measured and volumes calculated. MR volumetry was performed using a semiautomatic software tool. To validate the correctness and feasibility of the volume formula in macroscopic measurements, MR multiplanar reformation diameter measurements with subsequent volume calculation and semiautomatic MR volumes were correlated. Results: Semiautomatic MR volumetry yielded smaller volumes than manual measurement after dissection, irrespective of RF system used, target lesion size, and MR sequence. For the 3-cm lesion, only 43.3% (T1) and 41.5% (PD) of the entire necrosis are detectable. For the 5-cm lesion, only 40.8% (T1) and 37.2% (PD) are visualized in MRI directly after intervention. The correlation between semiautomatic MR volumes and calculated MR volumes was 0.888 for the T1-weighted sequence and 0.875 for the PD sequence. Conclusion: After correlation of semiautomatic MR volumes and calculated MR volumes, it seems reasonable to use the respective volume formula for macroscopic volume calculation. Hyperacute MRI after ex vivo intervention may result in the underestimation of the real expansion of the produced necrosis zone. This must be kept in mind when using MRI for validating ablation success directly after RFA. One reason for the discrepancy between macroscopic and MRI appearance immediately after RFA may be that the transitional zone shows no or only partially visible MR signal change.

Initial clinical experience with a quadrupole butterfly coil for spinal injection interventions in an open MRI system at 1.0 tesla

Abstract Purpose: To report our initial clinical experience with a new magnetic resonance imaging (MRI) quadrupole coil that allows interventions in prone position. Materials and methods: Fifteen patients (seven women, eight men; average age, 42.8 years) were treated in the same 1.0-Tesla Panorama High Field Open (HFO) MRI system (Panorama HFO) using a quadrupole butterfly coil (Bfly) and compared with 15 patients matched for sex, age, and MR intervention using the MultiPurposeL coil (MPL), performed in conventional lateral decubitus position (all, Philips Medical Systems, Best, The Netherlands). All interventions were performed with a near-real-time proton density turbo spin echo (PD TSE) sequence (time to repeat/time to echo/flip angle/acquisition time, 600 ms/10 ms/90°/3 s/image). Qualitative and quantitative image analyses were performed, including signal intensity, signal-to-noise and contrast-to-noise ratio (SNR, CNR), contrast, and full width at half maximum (FWHM) measurements. Results: Contrast differed significantly between the needle and muscles (Bfly 0.27/MPL 0.17), as well as the needle and periradicular fat (0.13/0.24) during the intervention (both, p=0.029), as well as the CNR between muscles and the needle (10.61/5.23; p=0.010), although the FWHM values did not (2.4/2.2; p=0.754). The signal intensity of the needle in interventional imaging (1152.9/793.2; p=0.006) and the postinterventional SNR values of subcutaneous fat (15.3/28.6; p=0.007), muscles (6.6/11.8; p=0.011), and the CNR between these tissues (8.7/17.5; p=0.004) yielded significant differences. Conclusion: The new coil is a valid alternative for MR-guided interventions in an open MRI system at 1.0 tesla, especially if patients cannot (or prefer not to) be in a lateral decubitus position or if prone positioning yields better access to the target zone.

Fluid preinjection for microwave ablation in an ex vivo bovine liver model assessed with volumetry in an open MRI system

PURPOSE We aimed to detect possible differences in microwave ablation (MWA) volumes after different fluid preinjections using magnetic resonance imaging (MRI). MATERIALS AND METHODS MWA volumes were created in 50 cuboid ex vivo bovine liver specimens (five series: control [no injection], 10 mL water, 10 mL 0.9% NaCl, 10 mL 6% NaCl, and 10 mL 12% NaCl preinjections; n=10 for each series). The operating frequency (915 megahertz), ablation time (7 min), and energy supply (45 watts) were constant. Following MWA, two MR sequences were acquired, and MR volumetry was performed for each sequence. RESULTS For both sequences, fluid preinjection did not lead to significant differences in MWA ablation volumes compared to the respective control group (sequence 1: mean MWA volumes ranged from 7.0±1.2 mm [water] to 7.8±1.3 mm [12% NaCl] vs. 7.3±2.1 mm in the control group; sequence 2: mean MWA volumes ranged from 4.9±1.4 mm [12% NaCl] to 5.5±1.9 mm [0.9% NaCl] vs. 4.7±1.6 mm in the control group). The ablation volumes visualized with the two sequences differed significantly in general (P < 0.001) and between the respective groups (control, P ≤ 0.001; water, P < 0.001; 0.9% NaCl, P < 0.001; 6% NaCl, P ≤ 0.001; 12% NaCl, P < 0.001). The volumes determined with sequence 1 were closer to the expected ablation volume of 8 mL compared to those determined with sequence 2. CONCLUSION For the fluid qualities and concentrations assessed, there is no evidence that fluid preinjection results in larger coagulation volumes after MWA. Because ablation volumes determined by MRI vary with the sequence used, interventionalists should gain experience in how to interpret postinterventional imaging findings (with the MR scanner, sequences, and parameters used) to accurately estimate the outcome of the interventions they perform.