Automated segmentation and quantification of the healthy and diseased aorta in CT angiographies using a dedicated deep learning approach.

OBJECTIVES: To develop and validate a deep learning-based algorithm for segmenting and quantifying the physiological and diseased aorta in computed tomography angiographies. METHODS: CTA exams of the aorta of 191 patients (68.1 ± 14 years, 128 male), performed between 2015 and 2018, were retrospectively identified from our imaging archive and manually segmented by two investigators. A 3D U-Net model was trained on the data, which was divided into a training, a validation, and a test group at a ratio of 7:1:2. Cases in the test group (n = 41) were evaluated to compare manual and automatic segmentations. Dice similarity coefficient (DSC), mean surface distance (MSD), and Hausdorff surface distance (HSD) were extracted. Maximum diameter, effective diameter, and area were quantified and compared between both segmentations at eight anatomical landmarks, and at the maximum area of an aneurysms if present (n = 14). Statistics included error calculation, intraclass correlation coefficient, and Bland-Altman analysis. RESULTS: A DSC of 0.95 [0.94; 0.95] and an MSD of 0.76 [0.06; 0.99] indicated close agreement between segmentations. HSD was 8.00 [4.47; 10.00]. The largest absolute errors were found in the ascending aorta with 0.8 ± 1.5 mm for maximum diameter and at the coeliac trunk with - 30.0 ± 81.6 mm2 for area. Results for absolute errors in aneurysms were - 0.5 ± 2.3 mm for maximum diameter, 0.3 ± 1.6 mm for effective diameter, and 64.9 ± 114.9 mm2 for area. ICC showed excellent agreement (> 0.9; p < 0.05) between quantitative measurements. CONCLUSIONS: Automated segmentation of the aorta on CTA data using a deep learning algorithm is feasible and allows for accurate quantification of the aortic lumen even if the vascular architecture is altered by disease. KEY POINTS: • A deep learning-based algorithm can automatically segment the aorta, mostly within acceptable margins of error, even if the vascular architecture is altered by disease. • Quantifications performed in the segmentations were mostly within clinically acceptable limits, even in pathologically altered segments of the aorta.

4D flow CMR analysis comparing patients with anatomically shaped aortic sinus prostheses, tube prostheses and healthy subjects introducing the wall shear stress gradient: a case control study.

BACKGROUND: Anatomically pre-shaped sinus prostheses (SP) were developed to mimic the aortic sinus with the goal to preserve near physiological hemodynamic conditions after valve-sparing aortic root replacement. Although SP have shown more physiological flow patterns, a comparison to straight tube prosthesis and the analysis of derived quantitative parameters is lacking. Hence, this study sought to analyze differences in aortic wall shear stress (WSS) between anatomically pre-shaped SP, conventional straight tube prostheses (TP), and age-matched healthy subjects) using time-resolved 3-dimensional flow cardiovascular magnetic resonance (4D Flow CMR). Moreover, the WSS gradient was introduced and analyzed regarding its sensitivity to detect changes in hemodynamics and its dependency on the expression of secondary flow patterns. METHODS: Twelve patients with SP (12 male, 62 ± 9yr), eight patients with TP (6 male, 59 ± 9yr), and twelve healthy subjects (2 male, 55 ± 6yr) were examined at 3 T with a 4D Flow CMR sequence in this case control study. Six analysis planes were placed in the thoracic aorta at reproducible landmarks. The following WSS parameters were recorded: WSSavg (spatially averaged over the contour at peak systole), max. WSSseg (maximum segmental WSS), min. WSSseg (minimum segmental WSS) and the WSS Gradient, calculated as max. WSSseg - min. WSSseg. Kruskal-Wallis- and Mann-Whitney-U-Test were used for statistical comparison of groups. Occurrence and expression of secondary flow patterns were evaluated and correlated to WSS values using Spearman's correlation coefficient. RESULTS: In the planes bordering the prosthesis all WSS values were significantly lower in the SP compared to the TP, approaching the physiological optimum of the healthy subjects. The WSS gradient showed significantly different values in the four proximally localized contours when comparing both prostheses with healthy subjects. Strong correlations between an elevated WSS gradient and secondary flow patterns were found in the ascending aorta and the aortic arch. CONCLUSION: Overall, the SP has a positive impact on WSS, most pronounced at the site and adjacent to the prosthesis. The WSS gradient differed most obviously and the correlation of the WSS gradient with the occurrence of secondary flow patterns provides further evidence for linking disturbed flow, which was markedly increased in patients compared to healthy sub jects, to degenerative remodeling of the vascular wall.

Accuracy of pre-interventional computed tomography angiography post-processing software and extravascularly calibrated devices to determine vessel diameters: comparison with an intravascularly located calibrated catheter.

Background Accurate vessel sizing might affect treatment outcome of endovascular therapy. Purpose To compare accuracy of peripheral vessel diameter measurements using pre-interventional computed tomography angiography post processing software (CTA-PPS) and extravascularly located calibrated devices used during digital subtraction angiography (DSA) with an intravascular scaled catheter (SC). Material and Methods In 33 patients (28 men, mean age = 72 ± 11 years) a SC was used during DSA of the femoro-popliteal territory. Simultaneously, one scaled radiopaque tape (SRT) was affixed to the lateral thigh, one scaled radiopaque ruler (SRR) was positioned on the angiography table. For each patient, diameters of five anatomic landmarks were measured on DSA images after calibration using different scaled devices and CTA-PPS. Diameters were compared to SC (reference) and between groups of non-obese (NOB) and obese (OB) patients. Results In total, 660 measurements were performed. Compared to the reference, SRT overestimated the diameter by 1.2% (range = -10-12, standard deviation [SD] = 4.1%, intraclass correlation coefficient [ICC] = 0.992, 95% confidence interval [CI] = 0.989-0.992, P = 0.01), the SRR and CTA-PPS underestimated it by 21.3% (range = 1-47, SD = 9.4%, ICC = 0.864, 95% CI = 0.11-0.963, P = 0.08) and 3.2% (range = 17-38, SD = 9.7%, ICC = 0.976, 95% CI = 0.964-0.983, P = 0.01), respectively. Underestimation using the SRR was greatest in the proximal superficial-femoral artery (31%) and lowest at the P2 level of the popliteal artery (15%). In the NOB group, diameter overestimation of the SRT was 0.8% (range = 4-7, SD = 4.2%, B = 0.071, 95% CI = 0.293-0.435, P = 0.08) compared to the OB group of 1.6% (range = -7-4, SD = 2.9%, B = 0.010, 95% CI = 0.474-0.454, P = 0.96). Diameter underestimation of the SRR was 17.3% (range = 13-21, SD = 3.1%, B = 0.946, 95% CI = 0.486-1.405, P = 0.002) in the NOB group, 23.3% (range = 11-36, SD = 6.6%, B = 0.870, 95% CI = 0.268-1.472, P = 0.007) in the OB group. Conclusion For calibrated measurements SRT and CTA-PPS prove accurate compared to the reference, while SRR does not. Obesity has a significant impact on underestimation of diameter if SRR is used.

Follow-up of probably benign lesions in non-screening breast diagnostics.

PURPOSE: Our study addresses at the benefit of surveillance of probably benign lesions, detected outside mammographic screening, during a 3-year period. METHODS: 28,588 women (mean age 57 ± 12 years) were examined. Two independent radiologists read the mammogram as well as the supplemented ultrasound (in case of breast density ACR type 3 and 4). In the case of discordance a third expert considered whether further examination was indicated or not. RESULTS: 3,266 diagnostic procedures ended with BI-RADS 3 result and 2,512 (76.9 %) women underwent a follow-up examination. 295 (11.7 %) of them received assessment examination (imaging and/or biopsy) and 37 (12.5 %) (none of them palpable) ended with BI-RADS 6. This equals a tumor detection rate of 14.7/1,000. The ratio in situ:invasive was 7:10 (1:1.43) and the mean size was 11.1 ± 4.51 mm. In the total cohort, 536 carcinomas ended with BI-RADS 6 of them 17 % were in situ and 83 % were invasive breast cancers (ratio in situ:invasive 1:4.99), mean size was 13.8 ± 6.3 mm. The cancer detection ratio in these cases was 18.7/1,000. CONCLUSIONS: The amount of detected tumors at follow-up of women with preceding BI-RADS 3 equates the associated potential of malignancy.

Bare-Metal Stent Tracking with Magnetic Particle Imaging.

Purpose: Magnetic particle imaging (MPI) is an emerging medical imaging modality that is on the verge of clinical use. In recent years, cardiovascular applications have shown huge potential like, e.g., intraprocedural imaging guidance of stent placement through MPI. Due to the lack of signal generation, nano-modifications have been necessary to visualize commercial medical instruments until now. In this work, it is investigated if commercial interventional devices can be tracked with MPI without any nano-modification. Material and Methods: Potential MPI signal generation of nine endovascular metal stents was tested in a commercial MPI scanner. Two of the stents revealed sufficient MPI signal. Because one of the two stents showed relevant heating, the imaging experiments were carried out with a single stent model (Boston Scientific/Wallstent-Uni Endoprothesis, diameter: 16 mm, length: 60 mm). The nitinol stent and its delivery system were investigated in seven different scenarios. Therefore, the samples were placed at 49 defined spatial positions by a robot in a meandering pattern during MPI scans. Image reconstruction was performed, and the mean absolute errors (MAE) between the signals' centers of mass (COM) and ground truth positions were calculated. The stent material was investigated by magnetic particle spectroscopy (MPS) and vibrating sample magnetometry (VSM). To detect metallic components within the delivery system, nondestructive testing via computed tomography was performed. Results: The tracking of the stent and its delivery system was possible without any nano-modification. The MAE of the COM were 1.49 mm for the stent mounted on the delivery system, 3.70 mm for the expanded stent and 1.46 mm for the delivery system without the stent. The results of the MPS and VSM measurements indicate that besides material properties eddy currents seem to be responsible for signal generation. Conclusion: It is possible to image medical instruments with dedicated designs without modifications by means of MPI. This enables a variety of applications without compromising the mechanical and biocompatible properties of the instruments.

Medical Imaging Decision And Support (MIDAS): Study protocol for a multi-centre cluster randomized trial evaluating the ESR iGuide.

OBJECTIVES: Medical imaging plays an essential role in healthcare. As a diagnostic test, imaging is prone to substantial overuse and potential overdiagnosis, with dire consequences to patient outcomes and health care costs. Clinical decision support systems (CDSSs) were developed to guide referring physicians in making appropriate imaging decisions. This study will evaluate the effect of implementing a CDSS (ESR iGuide) with versus without active decision support in a physician order entry on the appropriate use of imaging tests and ordering behaviour. METHODS: A protocol for a multi-center cluster-randomized trial with departments acting as clusters, combined with a before-after-revert design. Four university hospitals with eight participating departments each for a total of thirty-two clusters will be included in the study. All departments start in control condition with structured data entry of the clinical indication and tracking of the imaging exams requested. Initially, the CDSS is implemented and all physicians remain blinded to appropriateness scores based on the ESR imaging referral guidelines. After randomization, half of the clusters switch to the active intervention of decision support. Physicians in the active condition are made aware of the categorization of their requests as appropriate, under certain conditions appropriate, or inappropriate, and appropriate exams are suggested. Physicians may change their requests in response to feedback. In the revert condition, active decision support is removed to study the educational effect. RESULTS/CONCLUSIONS: The main outcome is the proportion of inappropriate diagnostic imaging exams requested per cluster. Secondary outcomes are the absolute number of imaging exams, radiation from diagnostic imaging, and medical costs. TRIAL REGISTRATION NUMBER: Approval from the Medical Ethics Review Committee was obtained under protocol numbers 20-069 (Augsburg), B 238/21 (Kiel), 20-318 (Lübeck) and 2020-15,125 (Mainz). The trial is registered in the ClinicalTrials.gov register under registration number NCT05490290.

Heating of Large Endovascular Stents and Stent Grafts in Magnetic Particle Imaging-Influence of Measurement Parameters and Isocenter Distance.

PURPOSE: Magnetic particle imaging (MPI) is a tomographic imaging modality with the potential for cardiovascular applications. In this context, the extent to which stents are heated should be estimated from safety perspective. Furthermore, the influence of the measurement parameters and stent distance to the isocenter of the MPI scanner on stent heating were evaluated. MATERIALS AND METHODS: Nine different endovascular stents and stent grafts were tested in polyvinyl-chloride tubes. The stents had diameters from 10 to 31 mm, lengths between 25 and 100 mm and were made from stainless steel, nitinol or cobalt-chromium. The temperature differences were recorded with fiber-optic thermometers. All measurements were performed in a preclinical commercial MPI scanner. The measurement parameters were varied (drive field strengths: 3, 6, 9, 12 mT and selection field gradients: 0, 1.25 and 2.5 T/m). Furthermore, measurements with different distances to the scanner's isocenter were performed (100 to 0 mm). RESULTS: All stents showed heating (maximum 53.1 K, minimum 4.6 K). The stent diameter directly correlated with the temperature increase. The drive field strength influenced the heating of the stents, whereas the selection field gradient had no detectable impact. The heating of the stents decreased with increasing distance from the scanner's isocenter and thus correlated with the loss of the scanner's magnetic field. CONCLUSION: Stents can cause potentially harmful heating in MPI. In addition to the stent diameter and design, the drive field strength and the distance to the MPI scanner's isocenter must be kept in mind as influencing parameters.

Benefits of the quality assured double and arbitration reading of mammograms in the early diagnosis of breast cancer in symptomatic women.

OBJECTIVES: To address the benefits of double and arbitration reading regarding tumour detection rates, percentage of in situ tumours, and number (of patients) needed to send for expert reading (number needed to treat; NNT) for one additional tumour finding. METHODS: QuaMaDi is a quality assured breast cancer diagnosis programme; with two-view mammography (craniocaudal, mediolateral oblique) and, in case of breast density ACR 3 or 4, routine ultrasound imaging; and with independent double reading of all images. A consecutive sample of symptomatic women, i.e. women at risk for breast cancer, women aged 70 and above, and/or women with preceding BI-RADS III findings, was analysed. RESULTS: 28,558 mammograms were performed (mean age of women: 57.3 [standard deviation: 12.3] years). Discordant findings were present in 3,837 double readings and were sent for arbitration reading. After histopathological assessment, 52 carcinomas were found (thereof 32% in situ). These carcinomas accounted for 1.8 tumours per 1,000 examinations in the total cohort and increased the tumour detection rate up to 16.4/1,000. The NNT in discordant cases was 74. CONCLUSION: Double and arbitration reading appears to be a useful tool to ensure the quality of early detection of breast lesions in symptomatic women during indication-based, standardised mammography. KEY POINTS: • Quality assured breast cancer diagnosis is feasible outside organised screening structures. • Double and arbitration reading is beneficial for populations ineligible for screening. • Double and arbitration reading increases the tumour detection rate. • Double and arbitration reading increases the percentage of in situ cancers.

Five-year outcomes of the Bi- versus Trimodular EndurantTM stent-graft in 100 patients with infrarenal abdominal aortic repair.

BACKGROUND: Recent studies on the Endurant™ endografts mainly compared outcomes of the bimodular stent-graft to other manufacturer's endografts or reported results for cases outside manufacturer's instructions for use (IFU), while data on the experience of standard endovascular aortic repair (EVAR) of infrarenal abdominal aortic aneurysms (AAA) inside manufacturer's IFU comparing the bi- with the trimodular device is limited. METHODS: Inclusion criteria were: 1) infrarenal aneurysms (>50 mm diameter) treated by EndurantTM II (END II) or EndurantTM IIs (END IIs) stent-graft inside manufacturer's IFU; 2) available CTA with 1 mm reconstruction of the entire aorta prior to intervention. Endpoints comparing the devices included technical success, 30-day mortality, rate of complications (bleeding with conversion to open repair, stent-graft stenosis/occlusion, acute distal embolism, infection or postprocedural necessity of dialysis), endoleaks and reinterventions (5-year follow-up). Aneurysm sac diameters were compared between baseline preinterventional CTA and last post-interventional CTA. RESULTS: One hundred patients (90% male, mean age 74 years) treated with END II (N.=66) or END IIs (N.=34) were included. Technical success was 99%. One procedure-related active bleeding occurred ending up in surgical conversion (END II N.=1). 30d mortality was 0%. No initial type I/III endoleaks were present. Re-interventions were required in 19/100 (19%) of patients (END II N.=10; END IIs N.=9, P=0.17). The outcome of EVAR including technical success, 30d mortality, rate of complications, endoleaks and re-interventions showed no significant differences comparing END II/IIs. CONCLUSIONS: Five-year outcomes of EVAR show consistently safe and effective results for either END II or IIs device.

Bimodal Interventional Instrument Markers for Magnetic Particle Imaging and Magnetic Resonance Imaging-A Proof-of-Concept Study.

The purpose of this work was to develop instrument markers that are visible in both magnetic particle imaging (MPI) and magnetic resonance imaging (MRI). The instrument markers were based on two different magnetic nanoparticle types (synthesized in-house KLB and commercial Bayoxide E8706). Coatings containing one of both particle types were fabricated and measured with a magnetic particle spectrometer (MPS) to estimate their MPI performance. Coatings based on both particle types were then applied on a segment of a nonmetallic guidewire. Imaging experiments were conducted using a commercial, preclinical MPI scanner and a preclinical 1 tesla MRI system. MPI image reconstruction was performed based on system matrices measured with dried KLB and Bayoxide E8706 coatings. The bimodal markers were clearly visible in both methods. They caused circular signal voids in MRI and areas of high signal intensity in MPI. Both the signal voids as well as the areas of high signal intensity were larger than the real marker size. Images that were reconstructed with a Bayoxide E8706 system matrix did not show sufficient MPI signal. Instrument markers with bimodal visibility are essential for the perspective of monitoring cardiovascular interventions with MPI/MRI hybrid systems.

Free breathing 2D multi-slice real-time gradient-echo cardiovascular magnetic resonance imaging: impact on left ventricular function measurements compared with standard multi-breath hold 2D steady-state free precession imaging.

OBJECTIVE: Multi-breath hold cine-imaging (standard-2D-SSFP) is the standard technique for ventricular function assessment. However, image acquisition is time-consuming and breath holding is required. Ultrafast 2D real-time imaging (2D real time-SSFP) does not require breath holding, but spatial resolution is sacrificed. The accuracy of 2D real time-SSFP free-breathing ventricular function assessment by using an automated contour detection programme has not been systematically studied. METHODS AND RESULTS: Twenty-eight subjects (14 with impaired LV function) were investigated by 1.5 Tesla magnetic resonance imaging. Left ventricular short-axis images were acquired with multi-breath hold standard 2D-SSFP and free-breathing 2D real time-SSFP. LV-volumes (EDV, ESV), EF, and mass were determined using a semi-automated contour detection programme. EDV, ESV, EF, and mass were not significantly different between real time- and standard 2D-SSFP in subjects (absolute differences: EDV 3.2 +/- 0.7 mL, ESV 3.0 +/- 0.3 mL, EF 1.9 +/- 0.4%, mass 0.8 +/- 0.4 g; P > or = 0.78) and patients (absolute differences: EDV= 3.0 +/- 0.8 mL, ESV 3.3 +/- 1.0 mL, EF 0.9 +/- 0.5%, mass 0.9 +/- 0.5 g; P > or = 0.73). Automated contour detection required extensive manual correction for real-time imaging (< or = 86%). CONCLUSIONS: Differences in LV function measurements between real-time and standard 2D-SSFP are small, and not significant. Real-time SSFP may be used for rapid LV function assessment when examination time is limited.

Left ventricular function assessment using a fast 3D gradient echo pulse sequence: comparison to standard multi-breath hold 2D steady state free precession imaging and accounting for papillary muscles and trabeculations.

OBJECTIVE: Papillary muscles and trabeculae for ventricular function analysis are known to significantly contribute to accurate volume and mass measurements. Fast imaging techniques such as three-dimensional steady-state free precession (3D SSFP) are increasingly being used to speed up imaging time, but sacrifice spatial resolution. It is unknown whether 3D SSFP, despite its reduced spatial resolution, allows for exact delineation of papillary muscles and trabeculations. We therefore compared 3D SSFP ventricular function measurements to those measured from standard multi-breath hold two-dimensional steady-state free precession cine images (standard 2D SSFP). METHODS AND RESULTS: 14 healthy subjects and 14 patients with impaired left ventricularfunction underwent 1.5 Tesla cine imaging. A stack of short axis images covering the left ventricle was acquired with 2D SSFP and 3D SSFP. Left ventricular volumes, ejection fraction, and mass were determined. Analysis was performed by substracting papillary muscles and trabeculae from left ventricular volumes. In addition, reproducibility was assessed. EDV, ESV, EF, and mass were not significantly different between 2D SSFP and 3D SSFP (mean difference healthy subjects: -0.06 +/- 3.2 ml, 0.54 +/- 2.2 ml, -0.45 +/- 1.8%, and 1.13 +/- 0.8 g, respectively; patients: 1.36 +/- 2.8 ml, -0.15 3.5 ml, 0.86 +/- 2.5%, and 0.91 +/- 0.9 g, respectively; P > or = 0.095). Intra- and interobserver variability was not different for 2D SSFP (P > or = 0.64 and P > or = 0.397) and 3D SSFP (P > or = 0.53 and P > or = 0.47). CONCLUSIONS: Differences in volumes, EF, and mass measurements between 3D SSFP and standard 2D SSFP are very small, and not statistically significant. 3D SSFP may be used for accurate ventricular function assessment when papillary muscles and trabeculations are to be taken into account.

Mechanical rotational thrombectomy in long femoropopliteal artery and bypass occlusions: risk factors for periprocedural peripheral embolization.

PURPOSE: We aimed to examine lesion characteristics influencing technical outcome and periprocedural peripheral embolization (PPE) during percutaneous mechanical rotational thrombectomy (PMT) of long femoropopliteal artery and bypass occlusions. METHODS: Retrospectively, 65 consecutive patients (43 male patients, mean age 70±12 years; Rutherford category I-III), undergoing PMT (Rotarex®, Straub Medical AG) with acutely/subacutely occluded femoropopliteal arteries/bypasses were included. Occlusions (mean length, 217±98 mm) were treated by PMT followed by percutaneous transluminal angioplasty (PTA) plus drug-coated balloon or PTA plus stenting/stentgrafting. Technical success was defined as residual stenosis <30%. Follow-up included duplex ultrasound and ankle-brachial index (ABI) after 12 months. Endpoints were technical success, complications, improvement of Rutherford category, ABI, and patency (re-stenosis <50%). The influence of lesion length, duration, and thrombus density (measured in preinterventional computed tomography angiography) on technical success and PPE was analyzed. RESULTS: Technical success was 18% (12/65) after PMT alone, 92% (60/65) after additional means. Four patients (6%) underwent bypass surgery and one patient (2%) amputation. PPE occurred in 11% (7/65). During the 12-month follow-up, three patients (5%) were lost to follow-up. ABI increased from baseline 0.5±0.12 to 0.81±0.14 (p = 0.001) and Rutherford category increased by at least one level in 57 patients at 12-month follow-up (clinical success, 88%). At 12 months, primary patency was 57.4% (95% CI, 45.8%-68.9%) and secondary patency was 75.0% (95% CI, 59.8%-72.3%). As risk factors for PPE, we identified lesion length >200 mm (15%; 6/39; OR 4.5; 95% CI, 0.5-40; p = 0.014) and thrombus density ≤45 HU (20%; 2/10; OR 3.0; 95% CI, 0.2-38.9; p = 0.05). No significant relation between risk factors and technical success was found. CONCLUSION: PMT followed by PTA or implantation of stent (grafts) appears to be effective and safe for revascularization of acute/subacute long occlusions. Thrombus density <45 HU and lesion length above 20 cm represent risk factors for PPE during PMT.

Heating of an Aortic Stent for Coarctation Treatment During Magnetic Particle Imaging and Magnetic Resonance Imaging-A Comparative In Vitro Study.

PURPOSE: To evaluate heating of a redilatable stent for the treatment of aortic coarctation in neonates and small children in the new imaging modality magnetic particle imaging and established magnetic resonance imaging. MATERIALS AND METHODS: The cobalt-chromium stent (BabyStent, OSYPKA AG, Rheinfelden, Germany) has a stent design which allows for redilatation and adjustment of the diameter from 6 to 16 mm for a use in aortic coarctation. The stent loses its radial integrity while opening at predetermined breaking points at a diameter of 14 mm or 16 mm, respectively. We measured the temperature increase in the stent at different diameters during 7-min magnetic particle imaging and magnetic resonance imaging scans with fiber optic thermometers under static conditions surrounded by air. In magnetic particle imaging, stents with diameters from 6 to 16 mm were tested while in magnetic resonance imaging only stents with diameters of 6 mm and 14 mm were investigated exemplarily. RESULT: In magnetic particle imaging, the measured temperature differences increased up to 4.7 K with growing diameters, whereas the opened stents with discontinuous struts at 14 and 16 mm showed only minimal heating of max. 0.5 K. In contrast to magnetic particle imaging, our measurements showed no heating of the stents during magnetic resonance imaging under identical conditions. CONCLUSION: The BabyStent did show only slight heating in magnetic particle imaging and no detectable temperature increase in magnetic resonance imaging.

Navigation of a magnetic micro-robot through a cerebral aneurysm phantom with magnetic particle imaging.

Cerebral aneurysms are potentially life threatening and nowadays treated by a catheter-guided coiling or by a neurosurgical clipping intervention. Here, we propose a helically shaped magnetic micro-robot, which can be steered by magnetic fields in an untethered manner and could be applied for a novel coiling procedure. This is shown by navigating the micro-robot through an additively manufactured phantom of a human cerebral aneurysm. The magnetic fields are applied with a magnetic particle imaging (MPI) scanner, which allows for the navigation and tomographic visualization by the same machine. With MPI the actuation process can be visualized with a localization accuracy of 0.68 mm and an angiogram can be acquired both without any radiation exposure. First in-vitro phantom experiments are presented, showing an idea of a robot conducted treatment of cerebral aneurysms.

Magnetic Particle Imaging: In vitro Signal Analysis and Lumen Quantification of 21 Endovascular Stents.

PURPOSE: Endovascular stents are medical devices, which are implanted in stenosed blood vessels to ensure sufficient blood flow. Due to a high rate of in-stent re-stenoses, there is the need of a noninvasive imaging method for the early detection of stent occlusion. The evaluation of the stent lumen with computed tomography (CT) and magnetic resonance imaging (MRI) is limited by material-induced artifacts. The purpose of this work is to investigate the potential of the tracer-based modality magnetic particle imaging (MPI) for stent lumen visualization and quantification. METHODS: In this in vitro study, 21 endovascular stents were investigated in a preclinical MPI scanner. Therefore, the stents were implanted in vessel phantoms. For the signal analysis, the phantoms were scanned without tracer material, and the signal-to-noise-ratio was analyzed. For the evaluation of potential artifacts and the lumen quantification, the phantoms were filled with diluted tracer agent. To calculate the stent lumen diameter a calibrated threshold value was applied. RESULTS: We can show that it is possible to visualize the lumen of a variety of endovascular stents without material induced artifacts, as the stents do not generate sufficient signals in MPI. The stent lumen quantification showed a direct correlation between the calculated and nominal diameter (r = 0.98). CONCLUSION: In contrast to MRI and CT, MPI is able to visualize and quantify stent lumina very accurately.

MR-guided liver biopsy within a short, wide-bore 1.5 Tesla MR system.

The purpose of this study was to evaluate the diagnostic efficacy of magnetic resonance (MR)-guided biopsy of focal liver lesions within a short, wide-bore 1.5-T MR system and to determine the duration and accuracy of needle placement using MR fluoroscopy guidance in 25 patients. Accuracy of needle placement was evaluated in two orthogonal planes, and the out-of-plane angle of needle deflection was measured. Needle positioning was characterised subjectively as centred, peripheral, or exterior relative to the lesion. Exterior positioning was corrected by a step-by-step procedure. Surgical resection (n = 6), previous histologies (n = 8), or clinical/radiological follow-up (n = 11) served as the 'gold standard'. The guidance needle could be placed successfully using MR fluoroscopy in 20 of 25 patients (80%). Needle placement was rated as 'centred' in 11 and as 'peripheral' in nine patients. Median needle deflection was 2.6 degrees, with a median deviation of 3.4 mm. In five patients, the direct approach failed or was rated as 'exterior'; therefore, repositioning after needle stabilisation with a stainless-steel stylet was necessary. The diagnostic yield of all biopsies was: sensitivity 95.5%, specificity 100.0% and accuracy 96.0%. In conclusion, MR-guided biopsies in a short, wide-bore MR system yielded highly reliable biopsy results, and in most cases the direct approach with MR fluoroscopy guidance proved to be fast and accurate.

MRI of the small bowel: can sufficient bowel distension be achieved with small volumes of oral contrast?

Sufficient luminal distension is mandatory for small bowel imaging. However, patients often are unable to ingest volumes of currently applied oral contrast compounds. The aim of this study was to evaluate if administration of low doses of an oral contrast agent with high-osmolarity leads to sufficient and diagnostic bowel distension. Six healthy volunteers ingested at different occasions 150, 300 and 450 ml of a commercially available oral contrast agent (Banana Smoothie Readi-Cat, E-Z-EM; 194 mOsmol/l). Two-dimensional TrueFISP data sets were acquired in 5-min intervals up to 45 min after contrast ingestion. Small bowel distension was quantified using a visual five-grade ranking (5 = very good distension, 1 = collapsed bowel). Results were statistically compared using a Wilcoxon-Rank test. Ingestion of 450 ml and 300 ml resulted in a significantly better distension than 150 ml. The all-over average distension value for 450 ml amounted to 3.4 (300 ml: 3.0, 150 ml: 2.3) and diagnostic bowel distension could be found throughout the small intestine. Even 45 min after ingestion of 450 ml the jejunum and ileum could be reliably analyzed. Small bowel imaging with low doses of contrast leads to diagnostic distension values in healthy subjects when a high-osmolarity substance is applied. These findings may help to further refine small bowel MRI techniques, but need to be confirmed in patients with small bowel disorders.

Comparison of FDG-PET, PET/CT and MRI for follow-up of colorectal liver metastases treated with radiofrequency ablation: initial results.

PURPOSE: Morphologic imaging after radiofrequency ablation (RFA) of liver metastases is hampered by rim-like enhancement in the ablation margin, making the identification of local tumor progression (LTP) difficult. Follow-up with PET/CT is compared to follow-up with PET alone and MRI after RFA. METHODS AND MATERIALS: Sixteen patients showed 25 FDG-positive colorectal liver metastases in pre-interventional PET/CT. Post-interventional PET/CT was performed 24h after ablation and was repeated after 1, 3 and 6 months and then every 6 months. PET and PET/CT data were compared with MR data sets acquired within 14 days before or after these time points. Either histological proof by biopsy or resection, or a combination of contrast-enhanced CT at fixed time points and clinical data served as a reference. RESULTS: The 25 metastases showed a mean size of 20mm and were treated with 39 RFA sessions. Ten lesions which developed LTP received a second round of RFA; four lesions received three rounds of treatment. The mean follow-up time was 22 months. Seventy-two PET/CT and 57 MR examinations were performed for follow-up. The accuracy and sensitivity for tumor detection was 86% and 76% for PET alone, 91% and 83% for PET/CT and 92% and 75% for MRI, respectively. CONCLUSIONS: In comparison to PET alone, PET/CT was significantly better for detecting LTP after RFA. There were no significant differences between MRI and PET/CT. These preliminary results, however, need further verification.