Comparison of apparent diffusion coefficient values among different MRI platforms: a multicenter phantom study

PURPOSE:We aimed to compare apparent diffusion coefficient (ADC) values among magnetic resonance imaging (MRI) scanners from different vendors.MATERIALS AND METHODS:We used a custom-made phantom solution consisting of distilled water, 0.9% NaCl, 25% NaCl, and shampoo for diffusion-weighted MRI (DW-MRI) examinations. DW-MRI was performed with similar sequence parameters using six different 1.5 Tesla MR scanners (scanners A–F). ADC maps were automatically constructed for all DW-MR images (b factors of 0 and 1000 s/mm2). ADC measurements were performed using regions of interest and seven different software programs, including four different postprocessing workstations, two different picture archiving and communication systems, and operator console software for each MR scanner.RESULTS:The ADC values generated by scanners A and F were higher and those of scanner B were lower than those generated by the other scanners (P = 0.002). The intravendor difference in the ADC values averaged from scanners D, E, and F was statistically significant (P < 0.001). The difference between the ADC values obtained by scanners C and E was not statistically different (P = 0.15).CONCLUSION:ADC values may differ among different MRI systems used for DW-MRI. Thus, the MRI vendor should be considered when using DW-MRI in a clinical setting

Development of quality standards for multi-center, longitudinal magnetic resonance imaging studies in clinical neuroscience

Magnetic resonance imaging (MRI) data is generated by a complex procedure. Many possible sources of error exist which can lead to a worse signal. For example, hidden defective components of a MRI-scanner, changes in the static magnetic field caused by a person simply moving in the MRI scanner room as well as changes in the measurement sequences can negatively affect the signal-to-noise ratio (SNR). A comprehensive, reproducible, quality assurance (QA) procedure is necessary, to ensure reproducible results both from the MRI equipment and the human operator of the equipment. To examine the quality of the MRI data, there are two possibilities. On the one hand, water or gel-filled objects, so-called "phantoms", are regularly measured. Based on this signal, which in the best case should always be stable, the general performance of the MRI scanner can be tested. On the other hand, the actually interesting data, mostly human data, are checked directly for certain signal parameters (e.g., SNR, motion parameters). This thesis consists of two parts. In the first part a study-specific QA-protocol was developed for a large multicenter MRI-study, FOR2107. The aim of FOR2107 is to investigate the causes and course of affective disorders, unipolar depression and bipolar disorders, taking clinical and neurobiological effects into account. The main aspect of FOR2107 is the MRI-measurement of more than 2000 subjects in a longitudinal design (currently repeated measurements after 2 years, further measurements planned after 5 years). To bring MRI-data and disease history together, MRI-data must provide stable results over the course of the study. Ensuring this stability is dealt with in this part of the work. An extensive QA, based on phantom measurements, human data analysis, protocol compliance testing, etc., was set up. In addition to the development of parameters for the characterization of MRI-data, the used QA-protocols were improved during the study. The differences between sites and the impact of these differences on human data analysis were analyzed. The comprehensive quality assurance for the FOR2107 study showed significant differences in MRI-signal (for human and phantom data) between the centers. Occurring problems could easily be recognized in time and be corrected, and must be included for current and future analyses of human data. For the second part of this thesis, a QA-protocol (and the freely available associated software "LAB-QA2GO") has been developed and tested, and can be used for individual studies or to control the quality of an MRI-scanner. This routine was developed because at many sites and in many studies, no explicit QA is performed nevertheless suitable, freely available QA-software for MRI-measurements is available. With LAB-QA2GO, it is possible to set up a QA-protocol for an MRI-scanner or a study without much effort and IT knowledge. Both parts of the thesis deal with the implementation of QA-procedures. High quality data and study results can be achieved only by the usage of appropriate QA-procedures, as presented in this work. Therefore, QA-measures should be implemented at all levels of a project and should be implemented permanently in project and evaluation routines

Multi-site harmonization of 7 Tesla MRI neuroimaging protocols

Increasing numbers of 7 T (7 T) magnetic resonance imaging (MRI) scanners are in research and clinical use. 7 T MRI can increase the scanning speed, spatial resolution and contrast-to-noise-ratio of many neuroimaging protocols, but technical challenges in implementation have been addressed in a variety of ways across sites. In order to facilitate multi-centre studies and ensure consistency of findings across sites, it is desirable that 7 T MRI sites implement common high-quality neuroimaging protocols that can accommodate different scanner models and software versions. With the installation of several new 7 T MRI scanners in the United Kingdom, the UK7T Network was established with an aim to create a set of harmonized structural and functional neuroimaging sequences and protocols. The Network currently includes five sites, which use three different scanner platforms, provided by two different vendors. Here we describe the harmonization of functional and anatomical imaging protocols across the three different scanner models, detailing the necessary changes to pulse sequences and reconstruction methods. The harmonized sequences are fully described, along with implementation details. Example datasets acquired from the same subject on all Network scanners are made available. Based on these data, an evaluation of the harmonization is provided. In addition, the implementation and validation of a common system calibration process is described

Health Care Rationing: What it Means

Examines issues related to rationing health care by applying its principles to radiology, and using examples from the budget limited British health system. Includes analysis of expenditures on life saving technology, and evaluation research

Design of a realistic PET-CT-MRI phantom

The validation of the PET image quality of new PET-MRI systems should be done against the image quality of currently available PET-CT systems. This includes the validation of new attenuation correction methods. Such validation studies should preferentially be done using a phantom. There are currently no phantoms that have a realistic appearance on PET, CT and MRI. In this work we present the design and evaluation of such a phantom. The four most important tissue types for attenuation correction are air, lung, soft tissue and bone. An attenuation correction phantom should therefore contain these four tissue types. As it is difficult to mimic bone and lung on all three modalities using a synthetic material, we propose the use of biological material obtained from cadavers. For the lung section a lobe of a pig lung was used. It was excised and inflated using a ventilator. For the bone section the middle section of a bovine femur was used. Both parts were fixed inside a PMMA cylinder with radius 10 cm. The phantom was filled with 18F-FDG and two hot spheres and one cold sphere were added. First a PET scan was acquired on a PET-CT system. Subsequently, a transmission measurement and a CT acquisition were done on the same system. Afterwards, the phantom was moved to the MRI facility and a UTE-MRI was acquired. Average CT values and MRI R 2 values in bone and lung were calculated to evaluate the realistic appearance of the phantom on both modalities. The PET data was reconstructed with CT-based, transmission-based and MRI-based attenuation correction. The activity in the hot and cold spheres in the images reconstructed using transmission-based and MRI-based attenuation correction was compared to the reconstructed activity using CT-based attenuation correction. The average CT values in lung and bone were -630 HU and 1300 HU respectively. The average R 2 values were 0.7 ms -1 and 1.05 ms -1 respectively. These values are comparable to the values observed in clinical data sets. Transmission-based and MRI-based attenuation correction yielded an average difference with CT- based attenuation correction in the hot spots of -22 % and -8 %. In the cold spot the average differences were +3 % and -8 %. The construction of a PET-CT-MRI phantom was described. The phantom has a realistic appearance on all three modalities. It was used to evaluate two attenuation correction methods for PET-MRI scanners

Advances in ENT imaging

Over the last ten years or so radiology has shown dramatic technological developments especially in cross sectional imaging and the investigation and management of the complex ENT patient has benefitted enormously. Plain radiographs are being utilised less and less as their limitations are becoming more apparent and various studies have shown for example a 75% discrepancy between plain sinus radiographs and coronal sinus CT in children1,2 . The incorporation of small and flexible ultrasound transducers with high-resolution imaging into the tips of endoluminal catheters has allowed good quality endoluminal ultrasound. Recently endolaryngeal ultrasound has been clinically evaluated in 38 patients with a variety of laryngeal pathology including vocal fold polyps, laryngeal cysts, chronic laryngitis, epithelial dysplasia and cancer 5 . Using this technique tumour size and infiltration could be measured and involvement of the thyroid cartilage or anterior commissure could be visualised. Not surprisingly it was not able to detect any specific changes in the sonographic picture of patients suffering from chronic laryngitis, epithelial dysplasia or microinvasive cancer. Although these results are encouraging, its relative lack of availability will result in it only having a limited role in evaluating laryngeal pathology.peer-reviewe