Ultrasound Quality Assurance – Getting the users involved

IAPM 3rd Annual Scientific Meeting 2012

334 artefact occurs in both colour and power Doppler ultrasound imaging and manifests as a false depiction of colour velocity information in stationary soft tissue and therefore can cause significant misdiagnosis of areas of flow within the patient. It has been hypothesised that it is generated due to a strongly reflecting medium composed of individual reflectors and therefore becomes a clinical concern when parenchymal calcifications are encountered. (Tsao et al., 2006). The aim of this study was to investigate the occurrence and magnitude of this artefact across a range of ultrasound scanners and to monitor the effects on the artefact of varying image acquisition parameters. A range of phantoms were produced that could reproducibly recreate the Twinkle artefact, the presence of which was quantified in a range of scanners (Zonare, Siemens Antares, Philips HDI and IU22). These phantoms included both fine and coarse structures as well as a flow channel in one of the phantoms, through which blood mimicking fluid was pumped. A semi-quantitative grading system was implemented and instrument controls such as pulse repetition frequency (PRF), colour write priority, greyscale gain and depth of focal zone were varied in order

to determine their impact on the Twinkle artefact. Instrument control settings were found to significantly affect the intensity of this artefact, predominantly PRF showed a significant increase in the presence of this artefact. Furthermore, the extent of the artefact varied greatly across the range of scanners with Siemens Antaries and Zonare being most sensitive to the artefact. The implication of this study has shown the Twinkle artefact to be dependent on scanner specifications and instrumental parameters. With careful image optimisation, a reduction or elimination of the artefact can be achieved. References Tsao, T.-F., Kang, R.-J., Tyan, Y.-S., Gueng, M.-K., Lee, T., & Lee, S.-K. (2006). Color Doppler Twinkling Artifact Related to Chronic Pancreatitis with Parenchymal Calcification. Acta Radiologica, 47(6), 547e548. Keywords: Colour Doppler, Twinkle artefact, Doppler test phantom

Evaluation of CIRS string Doppler phantom as a test tool for use in a Doppler Ultrasound Quality Assurance program JACINTA BROWNE1, SEAN COURNANE2 and ANDREW FAGAN3 1

Dublin Institute of Technology, Ireland, 2Medical Physics and Bioengineering, St. James’s Hospital, Ireland, 3Centre for Advanced Medical Imaging, St. James’s Hospital/Trinity College Dublin, Ireland

Abstract: Ultrasound Doppler systems are routinely used to perform blood flow velocity measurements which assist in the clinical assessment and diagnosis of vascular. Doppler measurements of peak velocities for vascular applications provide an indication of the degree of the stenosis which will ultimately assist in deciding how a patient is managed. It is imperative that Doppler systems are capable of accurately measuring blood flow velocities to ensure correct diagnosis and appropriate patient treatment; therefore such systems should be evaluated regularly as part of a Quality Assurance program. Although a range of Doppler test phantoms have been developed for quality control (QC) purposes to establish the measurement accuracy and stability of Doppler systems only a limited number of such test phantoms are commercially available, the easiest of these devices to operate is the String Phantom. Currently, only one string Doppler phantom is commercially available, namely the CIRS Model 043. In this study an evaluation of the performance of this test device was carried out as a number of problems currently exist with it such as the filament type, the fact that the filament passes through

a watereair interface and vibrations from the motor. This study has established that the braided-silk filament, provided with the phantom, should not be used as it introduces errors of as much as 24% for the mean velocity accuracy and 20% for the intrinsic spectral broadening (ISB) depending on the soak time of the filament. Rather, to avoid such errors it is advised that the phantom be retrofitted with a filament made from an O-ring rubber. While this eliminates the temporal changes in backscatter seen with the braided-silk filament, further discrepancies were observed, even with an O-ring filament, when the filament velocity was set in the range 26e44 cm/s, where a resonance effect significantly increased the variability of the maximum velocity accuracy and ISB measurements. This was most likely as a result of the imposed vibrations from the motor, which is mounted directly onto the tank wall; hence, it would prove practical to avoid taking measurements in this velocity range where resonance effects are observed. Keywords: String phantom, Doppler Ultrasound Quality Assurance program

Ultrasound Quality Assurance e Getting the users involved AOIFE O’BRIEN1 and MICHAEL TOWEY2 1

University Hospital Galway, Ireland, 2Portiuncula Hospital Ballinasloe, Ireland

Abstract: The use of diagnostic ultrasound in the acute hospital setting has increased dramatically over the last few years. This is due to a number of factors. Perhaps most significantly, technological advances have led to the availability of smaller, cheaper scanners suitable for point-of-care scanning with a concomitant increase in clinical applications and users. We have observed a 10-fold increase in the number of diagnostic ultrasound machines at Galway University Hospitals over the past 10 years. This large increase in the quantity and diversity of diagnostic ultrasound equipment enriches clinical care but presents a challenge for support staff involved in acceptance testing, maintenance and routine quality assurance. The increased workload required to perform quality control testing and the associated administration

can become prohibitive. This is a particular challenge for diagnostic ultrasound equipment that does not fall under the remit of the radiology department and therefore does not have the same support structure in place to manage imaging equipment. Attitudes towards quality assurance testing in ultrasound vary greatly between individuals. The fact that diagnostic ultrasound is viewed as a relatively safe imaging modality, coupled with the lack of legislation and the relative subjectivity of some test methods has led to the view that quality testing of diagnostic ultrasound is either unnecessary or ineffective. In 2009, a risk-based quality assurance programme was initiated for diagnostic ultrasound at Galway University Hospitals. The programme aims to meet the challenges posed by increasing equipment numbers and the diversification of

IAPM 3rd Annual Scientific Meeting 2012 clinical applications. It focuses on the importance of user involvement for frequent (monthly) user QA based on IPEM report 102. We have found this approach very beneficial and there are plans to expand

335 the program to a number of other hospitals in the near future. This paper will present our experiences to date. Keywords: QA ultrasound quality-assurance

Advanced neuroimaging for pre-surgical planning: Implementation challenges Dr. CHRISTINA SIMOES-FRANKLIN1, Dr. SEAMUS LOOBY2 and Mr. DONNCHA O’BRIEN3 1 MPCE Department, Beaumont Hospital, Dublin, Ireland, 2Department of Radiology, Beaumont Hospital, Ireland, 3Department of Neurosurgery, Beaumont Hospital, Ireland

Abstract: Since the birth of functional magnetic resonance imaging (fMRI) in the 90’s and more recently of diffusion tensor imaging (DTI), several clinical applications of these techniques have emerged, however the most widespread clinical trend is their use for pre-surgical planning. The goal of a neurosurgical procedure is to maximize the resection of the lesion (e.g. tumour, vascular malformation, epileptic foci) while minimizing permanent injury, which can be caused either by damaging the cortical areas immediately surrounding the lesion or the white matter tracks at the depths of the lesion. Advanced neuroimaging prior to surgery enables the neurosurgical team to plan the procedure and to envisage its complications, resulting in reduced surgical and recovery times and ultimately reduced morbidity. Furthermore, the coregistered datasets can also be used during neuronavigation although with limited reliability, due to the non-linear brain shift that occurs following the removal of the skull. Despite the clear benefits of pre-surgical mapping, implementing such a service in a busy clinical environment poses some challenges; additional MRI sequences result in increasing scanner occupancy, revision and standardization of acquisition protocols is necessary to achieve

reliable brain activations in shorter times, and the complexity of the data analysis requires a multidisciplinary team of experts. During the past year, a pre-surgical planning unit has been implemented in Beaumont Hospital. Motor fMRI and DTI data are acquired with a 1.5T Siemens Magnetom Avanto and transferred into PACS. The raw data is retrieved and transferred to a Linux workstation where is further analysed with SPM8 and Slicer software packages. Functional and tractography results are coregistered and superimposed on a high-resolution anatomical image and a three-dimensional reconstruction of the tumour and white fibre tracks surrounding it is generated. This 3D map can be uploaded in the operating theatre for review prior and during surgery. Future work will address some of the challenges facing the clinical implementation of advanced neuroimaging in neurosurgery, such as the standardization of acquisition protocols for language and memory mapping and the integration of the coregistered maps into PACS and neuronavigation systems. Keywords: Neuroimage, Functional MRI, Diffusion tensor imaging, Pre-surgical mapping, Neurosurgery

Effect on diagnostic image quality of 3D warping registration algorithms for MR angiography in the lower legs ANDREW J. FAGAN1, DANIEL FOLEY1, JACINTA E. BROWNE2, BARRY SHEANE1, DEARBHAIL O’DRISCOLL1, NIALL SHEEHY1 and JAMES F. MEANEY1 1

Centre for Advanced Medical Imaging, St. James’s Hospital/Trinity College Dublin, Ireland, 2Medical Ultrasound Physics and Technology Group, School of Physics and FOCAS Institute, Dublin Institute of Technology, Dublin, Ireland

Abstract: Mis-registration artefacts are known to reduce the image quality in contrast-enhanced MR angiography (CE-MRA), particularly whole body studies where table motion is involved. A previous inhouse study revealed a significant improvement in image quality following use of a conventional registration algorithm. The aim of this study was to evaluate a new generation of algorithms specifically designed to deal with the signal intensity changes arising from the use of a contrast agent, as in CE-MRA. Three warping algorithms were evaluated: AIR (used in the original study), and two algorithms (ITK and SEMI) designed for use with dynamic contrast enhanced MRI but not previously applied to MRA. 3T MR Images of 27 patients were acquired using a 3D-T1-weighted GRE sequence (resolution 0.9 mm3). Four expert observers visually assessed the images. Contrast-to-noise ratios were calculated using CNR ¼ (SIArtery e SITissue)/SDTissue. A measure of vessel integrity was determined by segmenting out a vessel within a RoI for each patient and calculating the resulting vessel volume. Statistical analysis was performed using the Friedman nonparametric analysis

on ranks for the clinical evaluation, and a paired-sample t-test was used to analyse the CNR and vessel volume for each algorithm. Each algorithm was found by all observers to improve the image quality (p < 0.05), with SEMI judged to perform better than AIR by all (p < 0.05), while Slicer was found to be better than AIR by 3 out 4 of the observers (p < 0.05). The improvement of SEMI compared to Slicer was significant only for one observer (p < 0.05). Although AIR removed more background tissue signal than SEMI or Slicer, it was found to degrade the vessel sharpness and integrity. AIR and SEMI had a significantly higher CNR than Slicer, however no significant difference existed between AIR and SEMI. Both SEMI and Slicer had larger vessel volumes on the segmented datasets compared to AIR, illustrating the degradation of the vessel integrity caused by the AIR algorithm. In conclusion, the conventionally-used AIR algorithm is not suitable for use in MRA image registration. However, a newer generation of algorithms designed to deal with signal intensity changes demonstrate significant potential for application to MRA. Keywords: Angiography, MRI, Image registration

Paediatric CT e The DRL challenge COLM SAIDLEAR Children’s University Hospital, Dublin, Ireland

Abstract: Recent publications and audits have highlighted the complexities associated with establishing dose reference levels

(DRL’s) in paediatric computed tomography (CT). National and international surveys are population based surveys in general and