Image quality is resilient against tube voltage variations in post-mortem skeletal radiography with a digital flat-panel detector

In recent phantom studies low-contrast detectability was shown to be independent from variations in tube voltage in digital radiography (DR) systems. To investigate the transferability to a clinical setting, the lower extremities of human cadavers were exposed at constant detector doses with different tube voltages in a certain range, as proposed in the phantom studies. Three radiologists independently graded different aspects of image quality (IQ) in a comparative analysis. The grades show no correlation between IQ and kV, which means that the readers were not able to recognize a significant IQ difference at different kV. Signal-to-noise and contrast-to-noise ratios showed no significant differences in IQ despite the kV-setting variations. These findings were observed from a limited kV range setting. Higher kV-settings resulted in lowest patient exposure at constant IQ. These results confirm the potential of DR-systems to contribute to standardization of examination protocols comparable to computed tomography. This may prevent the trend to overexpose. Further investigations in other body regions and other DR-systems are encouraged to determine transferability.

Improvement of Radiological Teaching - Effects of Focusing of Learning Targets and Increased Consideration of Learning Theory Knowledge

PURPOSE

Based on evaluation and examination results of students, a necessity for improvement of so far purely instructor-based radiological teaching at the local institution was determined. Aim of our study was to use one out of eight seminars to exemplify adaptation of the teaching concept according to learning theory knowledge, to determine the resulting effects and to interpret them.

MATERIALS AND METHODS

The institutional review board approved the prospective study of the seminar conversion, which was performed after the end of the winter semester 2015/2016. Didactically, this included a course split into online preparation, attendance phase and online follow-up with integration of interactive scaffolding, practice-oriented clinical teaching according to Stanford, Peyton skills transfer and extensive feedback into the attendance phase. At the beginning and at the end of each course, each student filled in identical, standardized questionnaires (n = 256 before and after conversion) using a 5-point Likert scale (1: very good; to 5: deficient) and additionally answered two randomly chosen written examination questions from a content-adapted questionnaire pool of the last five years. For statistical evaluation, the Mann-Whitney U-Test was used for evaluation data and Fisher's Exact test for exam questions.

RESULTS

Before/after conversion, the subjective total evaluation score of students was 3.22 (mean value) ± 1.51 (standard deviation) / 1.66 ± 0.78 (p < 0.001) and the objective proportion of correctly answered examination questions in the respective cohort at the beginning of the seminar 37.7/53.9 % and at the end of the seminar 55.1/84.6 % (p < 0.001).

CONCLUSION

The conversion of the test seminar resulted in both a better evaluation of the teaching unit by the students (evaluation) and a considerably higher rate of correctly answered examination questions from past state examinations (learning success). This supports transferring the concept to comparable teaching units.

KEY POINTS

· Radiological teaching allows integration of current learning theory concepts with reasonable effort.. · In a test seminar this improved the evaluation results of the teaching unit by the students.. · In addition, this also led to a higher rate of correctly answered examination questions from past state examinations.. · This supports further steps towards excellent radiological teaching..

CITATION FORMAT

· Wirth S, William Y, Paolini M et al. Improvement of Radiological Teaching - Effects of Focusing of Learning Targets and Increased Consideration of Learning Theory Knowledge. Fortschr Röntgenstr 2018; 190: 161 - 174.

[Pretreatment mass casualty incident workflow analysis : Comparison of two level 1 trauma centers]

BACKGROUND

Mass casualty incidents (MCI) have particularly high demands on patient care processes but occur rather rarely in daily hospital routine. Therefore, it is common to use simulations to train staff and to optimize institutional processes.

OBJECTIVES

Aim of study was to compare the pre-therapeutic in-house workflow of two differently structured level 1 trauma sites in the case of a simulated mass casualty incident (MCI).

MATERIALS AND METHODS

A MCI of 70 patients was simulated by actors in a manner that was as realistic as possible. The on-site triage assigned 7 cases to trauma site A with relatively long in-house distances and 4 patients to an independent trauma site B in which these distances were relatively short. During in-house treatment, time intervals for reaching milestones were measured and compared using the Mann-Whitney U test.

RESULTS

As no simultaneous patient arrival occurred, the Patient Distribution Matrix proved to be effective. Site A needed more time (minutes) from admission to endpoints (A: 31.85 ± 7.99; B: 21.62 ± 4.76; p = 0.059). In detail, the time intervals were particularly longer for both patient stay in trauma room (A: 8.46 ± 3.02; B: 2.73 ± 0.78, p < 0.01) and transfer time to the CT room (A: 1.81 ± 0.62; B: 0.06 ± 0.03, p < 0.01). A shorter stay in the CT room did not compensate these effects (A: 8.86 ± 1.84; B: 10.40 ± 2.89, p = 0.571). For both sites, image calculation and distribution were relatively time consuming (17.36 ± 3.05).

CONCLUSIONS

Although short in-house distances accelerated pretherapeutic treatment processes significantly, both sites remained clearly within the "golden hour". The strongest potential bottleneck was the time interval until images were available at the endpoints.

Reduction of CT beam hardening artefacts of ethylene vinyl alcohol copolymer by variation of the tantalum content: evaluation in a standardized aortic endoleak phantom

OBJECTIVES

Our aim was to develop an aortic stent graft phantom to simulate endoleak treatment and to find a tantalum content (TC) of ethylene-vinyl-alcohol-copolymer that causes fewer computed tomography (CT) beam hardening artefacts, but still allows for fluoroscopic visualization.

METHODS

Ethylene-vinyl-alcohol-copolymer specimens of different TC (10-50 %, and 100 %) were injected in an aortic phantom bearing a stent graft and endoleak cavities with simulated re-perfusion. Fluoroscopic visibility of the ethylene-vinyl-alcohol-copolymer specimens was analyzed. In addition, six radiologists analyzed endoleak visibility, and artefact intensity of ethylene-vinyl-alcohol-copolymer in CT.

RESULTS

Reduction of TC significantly decreased CT artefact intensity of ethylene-vinyl-alcohol-copolymer and increased visibility of endoleak re-perfusion (p < 0.000). It also significantly decreased fluoroscopic visibility of ethylene-vinyl-alcohol-copolymer (R = 0.883, p ≤ 0.01), and increased the active embolic volumes prior to visualization (Δ ≥ 40 μl). Ethylene-vinyl-alcohol-copolymer specimens with a TC of 45-50 % exhibited reasonable visibility, a low active embolic volume and a tolerable CT artefact intensity.

CONCLUSIONS

The developed aortic stent graft phantom allows for a reproducible simulation of embolization of endoleaks. The data suggest a reduction of the TC of ethylene-vinyl-alcohol-copolymer to 45 -50 % of the original, to interfere less with diagnostic imaging in follow-up CT examinations, while still allowing for fluoroscopic visualization.

[Arterial closure devices. What device for which clinical situation?]

CLINICAL/METHODICAL ISSUE

Access site complications after endovascular catheterization sometimes require open surgery and negatively impair safety, patient comfort and reimbursement. Increasing numbers of procedures and patients with multiple anticoagulants as well as cost pressure explain the demand for an immediate and stable access site closure.

STANDARD RADIOLOGICAL METHODS

Manual compression followed by compression bandage and bed rest for 4-24 h is still the gold standard but is unable to prevent access site complications in all cases.

METHODICAL INNOVATIONS

Arterial vascular closure devices allow immediate and stable closure of the puncture channel either by suture or by implantation of occluding foreign bodies or gluing fluids.

PERFORMANCE

The safety has been proven in several clinical trials. The main advantage lies in closing large lumen access sites without surgery and in patients treated with multiple anticoagulants as well as in outpatient procedures.

ACHIEVEMENTS

They have become a valuable supplement to the interventional arsenal.

PRACTICAL RECOMMENDATIONS

The physician, however, has to decide between different systems and mechanisms with respect to patient constitution, selected access vessel and level of calcification and diameter. Furthermore, all systems require a defined training prior the first use.

Evaluation of the 6-F ExoSeal vascular closure device in antegrade femoral artery punctures

PURPOSE

To evaluate the safety, comfort, and efficacy of an extravascularly deployed bioabsorbable plug-based vascular closure device (VCD) for sealing 6-F antegrade access sites in patients requiring peripheral endovascular intervention.

METHODS

A single-center, single-arm, prospective study to evaluate the 6-F ExoSeal VCD in terms of technical success, adverse events, and patient comfort enrolled 59 unselected symptomatic patients (42 men; mean age 72.1 ± 9.3 years) suffering from peripheral artery disease in an 11-month period. Patients with high body mass index (BMI) or calcification at the access site were not excluded. Calcifications of the access vessel were scored as grades 1-4 from fluoroscopic images. The pain level during implantation was evaluated after the procedure using a visual rating scale.

RESULTS

Technical success rate was 98.3%; 1 primary device failure was converted to manual compression. In addition, 1 (1.7%) pseudoaneurysm, 2 (3.4%) minor hematomas, and 1 (1.7%) minor secondary bleeding were observed. There was no intravascular application of the device detected. Neither BMI, calcification of the access vessel (present in 74.6%, mean score 1.4 ± 1.1), age, nor blood clotting had any statistically significant influence on adverse events. In total, 55 (93.2%) patients felt no pain during the VCD implantation.

CONCLUSION

The tested VCD was safe, with an excellent technical success rate even in cases with severe access vessel calcification.

Oxygen-enhanced MRI of the lungs: intraindividual comparison between 1.5 and 3 tesla

PURPOSE

To assess the feasibility of oxygen-enhanced MRI of the lung at 3 Tesla and to compare signal characteristics with 1.5 Tesla.

MATERIALS AND METHODS

13 volunteers underwent oxygen-enhanced lung MRI at 1.5 and 3 T with a T 1-weighted single-slice non-selective inversion-recovery single-shot half-Fourier fast-spin-echo sequence with simultaneous respiratory and cardiac triggering in coronal orientation. 40 measurements were acquired during room air breathing and subsequently during oxygen breathing (15 L/min, close-fitting face-mask). The signal-to-noise ratio (SNR) of the lung tissue was determined with a difference image method. The image quality of all acquisitions was visually assessed. The mean values of the oxygen-induced relative signal enhancement and its regional coefficient of variation were calculated and the signal enhancement was displayed as color-coded parameter maps. Oxygen-enhancement maps were visually assessed with respect to the distribution and heterogeneity of the oxygen-related signal enhancement at both field strengths.

RESULTS

The mean relative signal enhancement due to oxygen breathing was 13 % (± 5.6 %) at 1.5 T and of 9.0 % (± 8.0 %) at 3 T. The regional coefficient of variation was significantly higher at 3 T. Visual and quantitative assessment of the enhancement maps showed considerably less homogeneous distribution of the signal enhancement at 3 T. The SNR was not significantly different but showed a trend to slightly higher values (increase of about 10 %) at 3 T.

CONCLUSION

Oxygen-enhanced pulmonary MRI is feasible at 3 Tesla. However, signal enhancement is currently more heterogeneous and slightly lower at 3 T.

Analysis of signal dynamics in oxygen-enhanced magnetic resonance imaging

OBJECTIVES

Oxygen-enhanced MRI (O2-MRI) is frequently based on a block paradigm consisting of a series of consecutive T1-weighted scans acquired during alternating blocks with inhalation of room air and of pure oxygen. This design results in a complex signal-time course for each pixel, which displays the oxygen wash-in and wash-out processes and provides spatially resolved information about the lung function. The purpose of the present study was to optimize the signal-time-course analysis to extract (pixelwise) the maximum amount of information from the acquired data, and to introduce an appropriate cross-correlation approach for data sets containing the oxygen wash-in and wash-out periods.

MATERIALS AND METHODS

O2-MRI data of 11 healthy volunteers were acquired with a multislice inversion-recovery single-shot turbo-spin-echo sequence at 1.5 Tesla; lung and spleen were manually segmented on all 44 acquired slices. Six different model functions were pixelwise fitted to the data and compared using the Akaike information criterion. Four different reference functions were compared for cross-correlation analysis.

RESULTS

The optimal model function is a piecewise exponential function (median enhancement in lung/spleen: 16.3%/14.8%) with different time constants for wash-in (29.4 seconds/72.7 seconds) and wash-out (25.1 seconds/29.6 seconds). As a new parameter, it contains the delay between switching the gas supply and the onset of the signal change (4.8 seconds/24.5 seconds). Optimal cross-correlation results were obtained with a piecewise exponential reference function, which was temporally shifted to maximize the correlation, yielding median correlation coefficients of 0.694 and 0.878, median time delays of 7.5 seconds and 38.6 seconds, and median fractions of oxygen-activated pixels of 83.6% and 92.2% in the lung and the spleen, respectively.

CONCLUSIONS

It was demonstrated that the pixelwise assessment of O2-MRI data are optimally performed with piecewise exponential functions. Cross-correlation analysis with a piecewise exponential reference function results in significantly higher fractions of oxygen-activated pixels than with rectangular functions.

[Upper abdominal pain with recurrent cholangitis and pyelonephritis]

A 38-year-old man presented with pain in the right upper abdomen combined with elevated C-reactive protein (5.37 mg/dl) and creatinine levels (2.0 mg/dl). The medical history revealed recurrent abdominal pain. Duplex sonography showed large intrahepatic cystic structures, partially combined with a ribbon-shaped flow signal inside, as well as multiple cysts in the kidneys. The following MRI identified these findings as dilatated bile ducts surrounding the portal vein branches. This is known as the central dot sign. Overall, this special constellation is indicative of Caroli's disease, a rare congenital cystic dilatation of the intrahepatic bile ducts. The imaging results substantiated the diagnosis, especially in combination with cystic renal disease and recurrent cholangitis. Depending on the grade of liver involvement the treatment is partial hepatectomy or, as in our case transplantation, which also eliminates the risk of associated cholangiocarcinoma.