Roland Syha

Automated Computed Tomography Dose-Saving Algorithm to Protect Radiosensitive Tissues Estimation of Radiation Exposure and Image Quality Considerations

Purpose:To evaluate radiation exposure and image quality in thoracic computed tomography (CT) using a new dose-saving algorithm to protect radiosensitive organs. Materials and Methods:For dose measurements, an Alderson RANDO phantom equipped with thermoluminescent dosimeters was used. The effective dose was calculated according to the International Commission on Radiologic Protection 103. Exposure was performed on a second-generation dual-source CT. The following parameters for thoracic CT were used: 160 effective mAs, 120 kV, scan range of 30 cm, collimation of 128 × 0.6 mm. For the acquisition, the tube current modulation type XCare was used, which reduces the tube current for anterior tube position to minimize direct exposure to anterior located organs. To compare differences, scans with and without XCare were performed. Objective signal-to-noise measurements were evaluated, and the subjective noise perception was rated in a 3-point scale (1: excellent, 3: affecting diagnostic accuracy) in 30 patients with a standard thoracic examination and a follow-up using XCare. Results:A substantial dose reduction in radiosensitive tissues was evident using the dose-saving algorithm XCare. Specifically, reductions of 35.2% for the female breast and 20.1% for the thyroid gland were measured, resulting in a decreasing effective whole-body dose of 8.0% and 14.3% for males and females, respectively. The objective and subjective evaluation of image quality showed no significant differences between both scan protocols (P > 0.05). Mean signal-to-noise ratio was 1.3 ± 0.2 and 1.2 ± 0.2 in scan protocols without and with XCare, respectively. The subjective scores at the level of the pulmonary trunk were 1.2 ± 0.4 and 1.4 ± 0.5 in standard chest scan and scans with the dose-saving algorithm XCare, respectively. Conclusions:The XCare technique protects radiosensitive organs like the female breast and the thyroid gland without affecting image quality. Therefore, this dose-saving algorithm may be used in thoracic CT examinations in male and female patients.

Endovascular Aneurysm Repair Using a Reverse Chimney Technique in a Patient With Marfan Syndrome and Contained Ruptured Chronic Type B Dissection

We report endovascular thoracic and abdominal aneurysm repair (EVAR) with reverse chimney technique in a patient with contained ruptured type B dissection. EVAR seems feasible as a bailout option in Marfan patients with acute life-threatening disease.

Perfusion measurements of the calf in patients with peripheral arterial occlusive disease before and after percutaneous transluminal angioplasty using Mr arterial spin labeling

To evaluate muscle perfusion in patients with peripheral arterial occlusive disease (PAOD) before and after percutaneous transluminal angioplasty (PTA) of the limb by means of MR arterial spin labeling (ASL) perfusion measurements during reactive hyperemia.

Rapid assessment of longitudinal relaxation time in materials and tissues with extremely fast signal decay using UTE sequences and the variable flip angle method.

Objectives:To develop suitable strategies for quantification of longitudinal relaxation time (T1) by means of ultrashort echo time (UTE) sequences and the variable flip-angle approach in materials and tissues with extremely fast signal decay. Materials and Methods:A recently published modified Ernst equation, which correctly accounts for in-pulse relaxation of transverse magnetization, was used to numerically determine optimal flip angles for reliable assessment of T1 in case of extremely short effective transverse relaxation time (T2*). Various ratios of repetition time (TR) to T1 and radiofrequency (RF) pulse duration (TRF) to T2* were evaluated. Theoretical considerations were applied to solid polymeric material (T2* = 0.295 milliseconds), and T1 quantification was performed using various optimized flip-angle approaches at different RF pulse durations (TRF = 0.1–0.4 milliseconds). Furthermore, in vivo measurement of T1 in cortical bone was exemplarily performed in 3 healthy volunteers to test the applicability of the proposed method in vivo. For in vitro and in vivo studies, MR imaging was performed on a 3 T whole-body MR system using a 3D UTE sequence with a rectangular excitation pulse and centric radial readout. Results:Optimal flip angles were shown to be strongly dependent on TR/T1 and TRF/T2* ratios. Exemplarily, longitudinal relaxation time of the investigated solid polymeric material was determined to T1 = 223.1 ± 3.1 milliseconds with RF pulse duration of TRF = 0.2 milliseconds, and 12 acquired flip angles ranging from 5 to 60 degrees. Using only 2 optimized flip angles (8 degrees, 44 degrees), T1 of the same material was determined to T1 = 223.8 ± 4.2 milliseconds in a markedly less acquisition time. In vivo evaluation of cortical bone was feasible and showed T1 values of 80.4 ± 25.1 milliseconds, exemplarily. Conclusions:Using the modified Ernst equation, it seems possible to rapidly evaluate 3D distribution of longitudinal relaxation time in materials and tissues with extremely fast signal decay by means of UTE sequences and only 2 measurements with optimized flip angles.

Ultrashort echo time MR imaging with off‐resonance saturation for characterization of pathologically altered Achilles tendons at 3 T

Off‐resonance radiofrequency saturation pulses applied prior to regular excitation in MR sequences can be used to modify signal contrast based on magnetization transfer and direct saturation effects. Clinical applicability and value of ultrashort echo time sequences combined with off‐resonance saturation pulses was tested in 16 healthy and 14 tendinopathic as well as paratendinopathic Achilles tendons in vivo at 3 T. A 3D ultrashort echo time sequence in combination with a gaussian off‐resonance saturation pulse (frequency offset: 1000–5000 Hz) was used to modify the detectable MR signal intensity from the Achilles tendon. Off‐resonance saturation ratio was calculated as the relative reduction in signal intensity under selective off‐resonance saturation in relation to a reference measurement without any saturation pulse. Off‐resonance saturation ratio in tendons of healthy volunteers ranged from 0.52 ± 0.06 (1000 Hz) to 0.24 ± 0.02 (5000 Hz), whereas symptomatic tendinopathic tendons (0.35 ± 0.04 to 0.17 ± 0.02) and asymptomatic tendinopathic tendons (0.41 ± 0.06 to 0.21 ± 0.02) showed significantly lower mean off‐resonance saturation ratio values. Off‐resonance saturation ratio values might provide a sensitive and quantitative marker for assessment of pathological microstructure alterations of the Achilles tendon. Magn Reson Med, 2013.

Magnetization transfer in human Achilles tendon assessed by a 3D ultrashort echo time sequence: quantitative examinations in healthy volunteers at 3T.

PURPOSE Magnetization transfer contrast (MTC) imaging provides insight into interactions between free and bounded water. Newly developed ultrashort echo time (UTE) sequences implemented on whole-body magnetic resonance (MR) scanners allow MTC imaging in tissues with extremely fast signal decay such as tendons. The aim of this study was to develop a technique for the quantification of the MT effect in healthy Achilles tendons in-vivo at 3 Tesla. MATERIALS AND METHODS 16 normal tendons of volunteers with no history of tendinopathy were examined using a 3D-UTE sequence with a rectangular on-resonant excitation pulse and a Fermi-shaped off-resonant MT preparation pulse. The frequency of the MT pulse was varied from 1 to 5 kHz. MT effects were calculated in terms of the MT ratio (MTR) between measurements without and with MT preparation. Direct saturation effects of MT preparation on the signal intensity were evaluated using numerical simulation of Bloch equations. One patient with tendinopathy was examined to exemplarily show changes of MTR under pathologic conditions. RESULTS Calculation of MTR data was feasible in all examined tendons and showed a decrease from 0.53 ± 0.05 to 0.25 ± 0.03 (1 kHz to 5 kHz) for healthy volunteers. Evaluation of variation with gender and dominance of ankle revealed no significant differences (p > 0.05). In contrast, the patient with confirmed tendinopathy showed MTR values between 0.36 (1 kHz) and 0.19 (5 kHz). CONCLUSION MT effects in human Achilles tendons can be reliably assessed in-vivo using a 3D UTE sequence at 3 T. All healthy tendons showed similar MTR values (coefficient of variation 10.0 ± 1.2 %). The examined patient showed a clearly different MT effect revealing a changed microstructure in the case of tendinopathy.

Humane metapneumovirus (HMPV) associated pulmonary infections in immunocompromised adults—Initial CT findings, disease course and comparison to respiratory-syncytial-virus (RSV) induced pulmonary infections

AIM To describe computed tomography (CT)-imaging findings in human metapneumovirus (HMPV)-related pulmonary infection as well as their temporal course and to analyze resemblances/differences to pulmonary infection induced by the closely related respiratory-syncytial-virus (RSV) in immunocompromised patients. MATERIALS AND METHODS Chest-CT-scans of 10 HMPV PCR-positive patients experiencing pulmonary symptoms were evaluated retrospectively with respect to imaging findings and their distribution and results were then compared with data acquired in 13 patients with RSV pulmonary infection. Subsequently, we analyzed the course of chest-findings in HMPV patients. RESULTS In HMPV, 8/10 patients showed asymmetric pulmonary findings, whereas 13/13 patients with RSV-pneumonia presented more symmetrical bilateral pulmonary infiltrates. Image analysis yielded in HMPV patients following results: ground-glass-opacity (GGO) (n=6), parenchymal airspace consolidations (n=5), ill-defined nodular-like centrilobular opacities (n=9), bronchial wall thickening (n=8). In comparison, results in RSV patients were: GGO (n=10), parenchymal airspace consolidations (n=9), ill-defined nodular-like centrilobular opacities (n=10), bronchial wall thickening (n=4). In the course of the disease, signs of acute HMPV interstitial pneumonia regressed transforming temporarily in part into findings compatible with bronchitis/bronchiolitis. CONCLUSIONS Early chest-CT findings in patients with HMPV-related pulmonary symptoms are compatible with asymmetric acute interstitial pneumonia accompanied by signs of bronchitis; the former transforming with time into bronchitis and bronchiolitis before they resolve. On the contrary, RSV-induced pulmonary infection exhibits mainly symmetric acute interstitial pneumonia.

Short-Term Exercise-Induced Changes in Hydration State of Healthy Achilles Tendons Can Be Visualized by Effects of Off-Resonant Radiofrequency Saturation in a Three-Dimensional Ultrashort Echo Time MRI Sequence Applied at 3 Tesla

Off‐resonant RF saturation influences signal intensity dependent on free and bound water fractions as well as the macromolecular content. The extent of interaction between these compartments can be evaluated by using the off‐resonance saturation ratio (OSR). Combined with UTE sequences quantification of OSR even in tendinous tissues with extremely fast signal decay is possible. The aim of this prospective study was to investigate short‐term exercise‐induced effects of hydration state of the Achilles tendon by means of OSR and tendon volume.

Diagnostic value of T1 and T2* relaxation times and off‐resonance saturation effects in the evaluation of achilles tendinopathy by MRI at 3T

To evaluate and compare the diagnostic value of T1, T2* relaxation times and off‐resonance saturation ratios (OSR) in healthy controls and patients with different clinical and morphological stages of Achilles tendinopathy.

Transarterial chemoembolization using drug eluting beads and subsequent percutaneous MR-guided radiofrequency ablation in the therapy of intermediate sized hepatocellular carcinoma

OBJECTIVE To evaluate safety, efficacy, survival and recurrence-free survival of transarterial chemoembolization (TACE) with drug eluting (DC) beads combined with MR-guided radiofrequency (RF) ablation for the treatment of hepatocellular carcinomas (HCC) larger than 3 cm. MATERIALS AND METHODS This retrospective study was approved by the institutional review board. 20 patients (69.6 years ± SD 8.8) with HCC underwent DC Bead TACE and subsequent MR-guided RF ablation. Treatment interval varied between 5 and 15 days. Mean HCC diameter was 39 mm ± SD 7 mm (range 31-50mm). Rates of recurrence-free survival and overall survival were estimated using the Kaplan-Meier method. RESULTS Technical success rate, primary and secondary technical effectiveness rate were 100%, 90% and 95%, respectively. Local tumour progression developed in one patient. Cumulative survival rates at 1, 3 and 5 years were 90% (Confidence Interval [CI]: 67%-97%), 50% (CI: 29%-70%), 27% (CI: 11%-51%) respectively. Median survival time was 37.4 months. During follow up (mean: 39.1 months ± SD 22.4; range 5-84 months), tumour progression in untreated liver developed in 14 cases. Cumulative recurrence-free survival rates at 1, 3 and 5 years were 48% (CI: 27-69%), 16% (5-39%), 16% (5-39%) respectively. Median recurrence-free survival time was 10.7 months. One major complication occurred due to misdiagnosed local recurrence. CONCLUSION In conclusion, we demonstrated that MR-guided RF ablation with subsequent DC Bead TACE is safe and effective in local tumour control in patients with intermediate sized HCC.