Low-field Magnetic Resonance Imaging Scanner Research Articles

Fast Quantitative MRI: Spiral Acquisition Matching-Based Algorithm (SAMBA) for Robust T1 and T2 Mapping

Conventional diagnostic images from Magnetic Resonance Imaging (MRI) are typically qualitative and require subjective interpretation. Alternatively, quantitative MRI (qMRI) methods have become more prevalent in recent years with multiple clinical and preclinical imaging applications. Quantitative MRI studies on preclinical MRI scanners are being used to objectively assess tissues and pathologies in animal models and to evaluate new molecular MRI contrast agents. Low-field preclinical MRI scanners (≤3.0T) are particularly important in terms of evaluating these new MRI contrast agents at human MRI field strengths. Unfortunately, these low-field preclinical qMRI methods are challenged by long acquisition times, intrinsically low MRI signal levels, and susceptibility to motion artifacts. In this study, we present a new rapid qMRI method for a preclinical 3.0T MRI scanner that combines a Spiral Acquisition with a Matching-Based Algorithm (SAMBA) to rapidly and quantitatively evaluate MRI contrast agents. In this initial development, we compared SAMBA with gold-standard Spin Echo MRI methods using Least Squares Fitting (SELSF) in in vitro phantoms and demonstrated shorter scan times without compromising measurement accuracy or repeatability. These initial results will pave the way for future in vivo qMRI studies using state-of-the-art chemical probes.

Does bore size matter?-A comparison of the subjective perception of patient comfort during low field (0.55 Tesla) and standard (1.5 Tesla) MRI imaging.

The purpose of the present study was to evaluate the subjectively perceived patient comfort during magnetic resonance imaging (MRI) examinations and to assess potential differences between a recently introduced low field MRI scanner and a standard MRI scanner. Among other characteristics, the low field MRI scanner differs from the standard MRI scanner by offering more space (wider bore size of 80 centimeter diameter) and producing less noise, which may influence the patient comfort. In total, 177 patients were surveyed after MRI scans with either the low field MRI scanner (n = 91, MAGNETOM Free.Max, Siemens Healthineers) or the standard MRI scanner (n = 86, MAGNETOM Avanto Fit, Siemens Healthineers). Patients rated different aspects of comfort on a 5 point Likert scale: (a) claustrophobia, (b) comfort of the scanner table, (c) noise level and (d) vertigo during the scanning procedure. In terms of claustrophobia and comfort of the scanner table, patients rated both MRI scanners similar (e.g., mean ratings for claustrophobia: standard MRI scanner = 4.63 ± 1.04, low field MRI scanner = 4.65 ± 1.02). However, when asked for a comparison, patients did favor the more spacious low field MRI scanner. In terms of noise level, the low field MRI scanner was rated significantly better (mean ratings: standard MRI scanner = 3.72 ± 1.46 [median 4 = "rather not unpleasant"], low field MRI scanner = 4.26 ± 1.22 [median 5 = "not unpleasant at all"]). Patients did not perceive any significant difference in terms of vertigo between both MRI scanners. The newly developed low field MRI scanner offers constructional differences compared to standard MRI scanners that are perceived positively by patients. Worth highlighting is the significantly lower noise level and the innovative bore diameter of 80 centimeter, which offers more space to the patients.

Usability of magnetic resonance images acquired at a novel low-field 0.55T scanner for brain radiotherapy treatment planning.

Low-field magnetic resonance imaging (MRI) may offer specific advantages over high-field MRI, e.g. lower susceptibility-dependent distortions and simpler installation. The study aim was to evaluate if a novel 0.55T MRI scanner provides sufficient image accuracy and quality for radiotherapy (RT) treatment planning. The geometric accuracy of images acquired at a low-field MRI scanner was evaluated in phantom measurements regarding gradient non-linearity-related distortions. Patient-induced B0-susceptibility changes were investigated via B0-field-mapping in ten volunteers. Patients were positioned in RT-setup using a 3D-printed insert for the head/neck-coil that was tested for sufficient signal-to-noise-ratio (SNR). The suitability of the MRI-system for detection of metastases was evaluated in eleven patients. In comparison to diagnostic images, acquired at ≥1.5T, three physicians evaluated the detectability of metastases by counting them in low- and high-field-images, respectively. The phantom measurements showed a high imaging fidelity after 3D-distortion-correction with (1.2±0.9) mm geometric distortion in 10cm radius from isocentre. At the edges remaining distortions were greater than at 1.5T. The mean susceptibility-induced distortions in the head were (0.05±0.05) mm and maximum 0.69mm. SNR analysis showed that optimised positioning of RT-patients without signal loss in the head/neck-coil was possible with the RT-insert. No significant differences (p=0.48) in detectability of metastases were found. The 0.55T MRI system provided sufficiently geometrically accurate and high-resolution images that can be used for RT-planning for brain metastases. Hence, modern low-field MRI may contribute to simply access MRI for RT-planning after further investigations.

Portable magnetic resonance imaging of patients indoors, outdoors and at home

Mobile medical imaging devices are invaluable for clinical diagnostic purposes both in and outside healthcare institutions. Among the various imaging modalities, only a few are readily portable. Magnetic resonance imaging (MRI), the gold standard for numerous healthcare conditions, does not traditionally belong to this group. Recently, low-field MRI technology companies have demonstrated the first decisive steps towards portability within medical facilities and vehicles. However, these scanners’ weight and dimensions are incompatible with more demanding use cases such as in remote and developing regions, sports facilities and events, medical and military camps, or home healthcare. Here we present in vivo images taken with a light, small footprint, low-field extremity MRI scanner outside the controlled environment provided by medical facilities. To demonstrate the true portability of the system and benchmark its performance in various relevant scenarios, we have acquired images of a volunteer’s knee in: (i) an MRI physics laboratory; (ii) an office room; (iii) outside a campus building, connected to a nearby power outlet; (iv) in open air, powered from a small fuel-based generator; and (v) at the volunteer’s home. All images have been acquired within clinically viable times, and signal-to-noise ratios and tissue contrast suffice for 2D and 3D reconstructions with diagnostic value. Furthermore, the volunteer carries a fixation metallic implant screwed to the femur, which leads to strong artifacts in standard clinical systems but appears sharp in our low-field acquisitions. Altogether, this work opens a path towards highly accessible MRI under circumstances previously unrealistic.

Development of a mobile low-field MRI scanner

Magnetic resonance imaging (MRI) allows important visualization of the brain and central nervous system anatomy and organization. However, unlike electroencephalography (EEG) or functional near infrared spectroscopy, which can be brought to a patient or study participant, MRI remains a hospital or center-based modality. Low magnetic field strength MRI systems, however, offer the potential to extend beyond these traditional hospital and imaging center boundaries. Here we describe the development of a modified cargo van that incorporates a removable low-field permanent magnet MRI system and demonstrate its proof-of-concept. Using phantom scans and in vivo T2-weighted neuroimaging data, we show no significant differences with respect to geometric distortion, signal-to-noise ratio, or tissue segmentation outcomes in data acquired in the mobile system compared to a similar static system in a laboratory setting. These encouraging results show, for the first time, MRI that can be performed at a participant’s home, community center, school, etc. Breaking traditional barriers of access, this mobile approach may enable imaging of patients and participants who have mobility challenges, live long distances from imaging centers, or are otherwise unable to travel to an imaging center or hospital.

Simultaneous imaging of hard and soft biological tissues in a low-field dental MRI scanner

Magnetic Resonance Imaging (MRI) of hard biological tissues is challenging due to the fleeting lifetime and low strength of their response to resonant stimuli, especially at low magnetic fields. Consequently, the impact of MRI on some medical applications, such as dentistry, continues to be limited. Here, we present three-dimensional reconstructions of ex-vivo human teeth, as well as a rabbit head and part of a cow femur, all obtained at a field strength of 260 mT. These images are the first featuring soft and hard tissues simultaneously at sub-Tesla fields, and they have been acquired in a home-made, special-purpose, pre-medical MRI scanner designed with the goal of demonstrating dental imaging at low field settings. We encode spatial information with two pulse sequences: Pointwise-Encoding Time reduction with Radial Acquisition and a new sequence we have called Double Radial Non-Stop Spin Echo, which we find to perform better than the former. For image reconstruction we employ Algebraic Reconstruction Techniques (ART) as well as standard Fourier methods. An analysis of the resulting images shows that ART reconstructions exhibit a higher signal-to-noise ratio with a more homogeneous noise distribution.

Dose uncertainty and resolution of polymer gel dosimetry using an MRI guided radiation therapy system’s onboard 0.35 T scanner

Magnetic Resonance Imaging (MRI) scanners are widely used for 3D gel dosimeters readout. However, limited access to MRI scanners is a challenge in MRI-based gel dosimetry. Recent clinical implementation of MRI-guided radiation therapy machines provides potential opportunities for onboard gel dosimetry using its MRI subsystem. The objective of this study was to investigate the feasibility of gel dosimetry using ViewRay’s onboard 0.35 T MRI scanner. A BANG® polymer gel dosimeter was irradiated by three beams of 3 × 3 cm2 field size. The T2 relaxation rate (R2) of the irradiated gel was measured using a Philips 1.5 T Ingenia MRI and a ViewRay 0.35 T onboard MRI and spin-echo pulse sequences. The number of signal averages (NSA) was set to 16 for the ViewRay acquisitions and one for the Philips 1.5 T MRI to achieve similar signal-to-noise ratios. The in-plane spatial resolution was 1.5 × 1.5 mm2 and the slice thickness was 5 mm. The relative dose uncertainty was obtained using R2 versus dose curves to compare the performance of dosimetry using the two different MRIs and field strengths. The dose uncertainty decreased from 12% at 2 Gy to 3.5% at 7.5 Gy at 1.5 T. The dose uncertainty decreased from 13% at 2 Gy to 4% at 7.5 Gy with NSA = 16 and 3 × 3 mm2 pixel size, and from 10.5% at 2 Gy to 3.2% at 7.5 Gy with NSA = 16 and denoised R2 maps (1.5 × 1.5 mm2 pixel size) at 0.35 T. The mean of dose resolution was 0.4 Gy at 1.5 T while the mean of dose resolution was 0.8 Gy and 0.64 Gy at 0.35 T by downsampling and denoising the R2 map, respectively. Therefore, comparable dose uncertainty was achievable using the ViewRay’s onboard 0.35 T and Philips 1.5 T MRI scanners. 3D gel dosimetry using onboard low-field MRI scanner provides ViewRay users a 3D high resolution dosimetry option besides film and ionization chamber.

A small-scale MRI scanner and complementary imaging method to visualize and quantify xylem embolism formation.

Magnetic resonance imaging (MRI) is a useful tool to image xylem embolism formation in plants. MRI scanners configured to accept intact plants are rare and expensive. Here, we investigate if affordable small-scale, custom-built low-field MRI scanners would suffice for the purpose. A small-scale, C-shaped permanent magnet was paired with open, plane parallel imaging gradients. The setup was small enough to fit between leaves or branches and offered open access for plant stems of arbitrary length. To counter the two main drawbacks of the system, low signal to noise and reduced magnetic field homogeneity, a multi-spin echo (MSE) pulse sequence was implemented, allowing efficient signal acquisition and quantitative imaging of water content and T2 signal relaxation. The system was tested visualizing embolism formation in Fagus sylvatica during bench dehydration. High-quality images of water content and T2 were readily obtained, which could be utilized to detect the cavitation of vessels smaller than could be spatially resolved. A multiplication of both map types yielded images in which filled xylem appeared with even greater contrast. T2 imaging with small-scale MRI devices allows straightforward visualization of the spatial and temporal dynamics of embolism formation and the derivation of vulnerability curves.

Feline hip joint anatomy in magnetic resonance images.

The aim of this study was to develop an anatomical model of the feline hip joint for low-field magnetic resonance imaging (LF-MRI) based on high-field magnetic resonance imaging (HF-MRI). The study was performed on six adult clinically healthy European shorthair cats, aged 1-3years, with body weight of 2.8-4.4kg. The animals were examined with the use of the Vet-MRI Grande Esaote LF (0.25T) scanner and high-field Siemens Magnetom TRIO (3T) MRI scanner. In the LF-MRI, most satisfactory results in T1-weighted images were obtained when TE was 26ms in all three planes and when TR was 350-950ms in the transverse plane, 950-1150ms in the sagittal plane and 520-750ms in the dorsal plane. In T2-weighted images, TE was 90ms in the transverse and dorsal plane and 120ms in the sagittal plane. The results were presented as images acquired with LF-MRI scanners in three planes. The slice thickness was 3mm for each plane. In LF-MRI, muscles in the hip joint region and round ligament were well visualized. Unlike in LF-MRI, the cross section of the femoral nerve was identified in HF-MRI scans. In examinations of the feline hip joint, the main limitations of LF-MRI were a lack of reliable contrast between articular cartilage and synovial fluid as well as longer scan time. Despite the above, LF-MRI images were characterized by good contrast between bones and the surrounding soft tissues.

Muscle volume reconstruction from several short magnetic resonance imaging sequences

The gold standard to determine muscle morphological parameters is magnetic resonance imaging (MRI). To measure large muscles like the vastus lateralis (VL) in one sequence, scanners with a large field of view (FOV) and a high flux density are needed. However, large scanners are expensive and not always available. The purpose of the current study was to develop a marker-based approach to reconstruct the VL from several separate MRI sequences, acquired with a low-field MRI scanner. The VL muscle of 21 volunteers was marked at one-third and two-third of thigh length using fish oil capsules. Three consecutive MRI sequences (i.e. proximal, medial and distal part) of the thigh were captured between the markers and the muscle insertion and origin. After a manual segmentation of the VL the muscle was reconstructed using the developed approach. The muscle volume, maximal anatomical cross-sectional area and length were 715.1 ± 93.4 cm3, 34.0 ± 4.0 cm2 and 34.4 ± 2.2 cm respectively. The procedure showed an average error between 0.9% and 2.2% for the reconstructed muscle volume, the averaged RMSD between the cross-sectional areas of two overlapping sequences were between 0.80 ± 0.71 cm2 and 0.88 ± 0.78 cm2. The proposed approach provides an appropriate accuracy for muscle volume assessment, as the estimated error for muscle volume calculation was quite small. The reconstruction quality depends mainly on the proper marker attachment and identification, as well as the spatial resolution of the image sequences. We are confident that the presented method can be used in most investigations regarding muscle morphology.

Bimodal TWMPI-MRI Hybrid Scanner—Coil Setup and Electronics

Magnetic particle imaging (MPI) was first presented in 2005. It is based on the nonlinear response of ferromagnetic material and the fact that the magnetization saturates at sufficiently high magnetic fields. In contrast to magnetic resonance imaging (MRI), MPI directly detects the concentration and distribution of superparamagnetic iron-oxide nanoparticles without any background of any tissue. To overcome this issue, a traveling wave MPI (TWMPI) device was combined with a low field MRI scanner to demonstrate the feasibility of a hybrid scanner, which contains both imaging modalities in a single device. The hardware of both separate approaches should be improved and optimized to reach higher fields and a higher resolution, especially for the MRI measurement. Therefore, the dynamic linear gradient array from the TWMPI scanner was modified in a way to produce also a homogenous magnetic field, which can be used for MRI.

Role of diffusion-weighted imaging in acute stroke management using low-field magnetic resonance imaging in resource-limited settings

A variety of imaging modalities exist for the diagnosis of stroke. Several studies have been carried out to ascertain their contribution to the management of acute stroke and to compare the benefits and limitations of each modality. Diffusion-weighted imaging (DWI) has been described as the optimal imaging technique for diagnosing acute ischemic stroke, yet limited evidence is available on the value of DWI in the management of ischemic stroke with low-field magnetic resonance (MR) systems. Although high-field MR imaging (MRI) is desirable for DWI, low-field scanners provide an acceptable clinical compromise which is of importance to developing countries posed with the challenge of limited availability of high-field units. The purpose of this paper was to systematically review the literature on the usefulness of DWI in acute stroke management with low-field MRI scanners and present the experience in Nigeria.

High-resolution small field-of-view magnetic resonance image acquisition system using a small planar coil and a pneumatic manipulator in an open MRI scanner.

Low-field open magnetic resonance imaging (MRI) is frequently used for performing image-guided neurosurgical procedures. Intraoperative magnetic resonance (MR) images are useful for tracking brain shifts and verifying residual tumors. However, it is difficult to precisely determine the boundary of the brain tumors and normal brain tissues because the MR image resolution is low, especially when using a low-field open MRI scanner. To overcome this problem, a high-resolution MR image acquisition system was developed and tested. An MR-compatible manipulator with pneumatic actuators containing an MR signal receiver with a small radiofrequency (RF) coil was developed. The manipulator had five degrees of freedom for position and orientation control of the RF coil. An 8-mm planar RF coil with resistance and inductance of 2.04[Formula: see text] and 1.00[Formula: see text] was attached to the MR signal receiver at the distal end of the probe. MR images of phantom test devices were acquired using the MR signal receiver and normal head coil for signal-to-noise ratio (SNR) testing. The SNR of MR images acquired using the MR signal receiver was 8.0 times greater than that of MR images acquired using the normal head coil. The RF coil was moved by the manipulator, and local MR images of a phantom with a 2-mm grid were acquired using the MR signal receiver. A wide field-of-view MR image was generated from a montage of local MR images. A small field-of-view RF system with a pneumatic manipulator was integrated in a low-field MRI scanner to allow acquisition of both wide field-of-view and high-resolution MR images. This system is promising for image-guided neurosurgery as it may allow brain tumors to be observed more clearly and removed precisely.

Analysis of Low-Field MRI Scanners for Evaluation of Shoulder Pathology Based on Arthroscopy.

Background:Many studies have compared the diagnostic capabilities of low-field magnetic resonance imaging (MRI) scanners to high-field MRI scanners; however, few have evaluated the low-field MRI diagnoses compared with intraoperative findings.Purpose:To determine the accuracy and sensitivity of low-field MRI scanners in diagnosing lesions of the rotator cuff and glenoid labrum.Study Design:Cohort study (diagnosis); Level of evidence, 3.Methods:Over a 2-year period, MRI examinations without intra-articular contrast were performed on 79 patients for shoulder pathologies using an in-office 0.2-T extremity scanner. The MRI examinations were read by board-certified, musculoskeletal fellowship–trained radiologists. All patients underwent shoulder arthroscopy performed by a single sports fellowship–trained orthopaedic surgeon within a mean time of 56 days (range, 8-188 days) after the MRI examination. The mean patient age was 54 years (range, 18-81 years). Operative notes from the shoulder arthroscopies were then retrospectively reviewed by a single blinded observer, and the intraoperative findings were compared with the MRI reports.Results:For partial-thickness rotator cuff tears, the sensitivity, specificity, positive predictive value, and negative predictive value were 85%, 89%, 79%, and 92%, respectively. For full-thickness rotator cuff tears, the respective values were 97%, 100%, 100%, and 98%. For anterior labral lesions, the values were 86%, 99%, 86%, and 99%, and for superior labral anterior-posterior (SLAP) lesions, the values were 20%, 100%, 100%, and 79%, respectively.Conclusion:Low-field MRI is an accurate tool for evaluation of partial- and full-thickness rotator cuff tears; however, it is not effective in diagnosing SLAP lesions. More information is needed to properly assess its ability to diagnose anterior and posterior labral lesions.

EFFECTS OF STIFLE FLEXION ANGLE AND SCAN PLANE ON VISIBILITY OF THE NORMAL CANINE CRANIAL CRUCIATE LIGAMENT USING LOW‐FIELD MAGNETIC RESONANCE IMAGING

Low-field magnetic resonance imaging (MRI) is commonly used to evaluate dogs with suspected cranial cruciate ligament injury; however, effects of stifle positioning and scan plane on visualization of the ligament are incompletely understood. Six stifle joints (one pilot, five test) were collected from dogs that were scheduled for euthanasia due to reasons unrelated to the stifle joint. Each stifle joint was scanned in three angles of flexion (90°, 135°, 145°) and eight scan planes (three dorsal, three axial, two sagittal), using the same low-field MRI scanner and T2-weighted fast spin echo scan protocol. Two experienced observers who were unaware of scan technique independently scored visualization of the cranial cruciate ligament in each scan using a scale of 0-3. Visualization score rank sums were higher when the stifle was flexed at 90° compared to 145°, regardless of the scan plane. Visualization scores for the cranial cruciate ligament in the dorsal (H (2) = 19.620, P = 0.000), axial (H (2) = 14.633, P = 0.001), and sagittal (H (2) = 8.143, P = 0.017) planes were significantly affected by the angle of stifle flexion. Post hoc analysis showed that the ligament was best visualized at 90° compared to 145° in the dorsal (Z = -3.906, P = 0.000), axial (Z = -3.398, P = 0.001), and sagittal (Z = -2.530, P = 0.011) planes. Findings supported the use of a 90° flexed stifle position for maximizing visualization of the cranial cruciate ligament using low-field MRI in dogs.

Analysis of Low-Field Magnetic Resonance Imaging Scanners for Evaluation of Knee Pathology Based on Arthroscopy.

Background:In recent years, few studies have evaluated low-field magnetic resonance imaging (MRI) diagnoses compared with intraoperative findings of the knee.Purpose:To determine the accuracy and sensitivity of low-field MRI scanners in diagnosing pathology of the menisci, cruciate ligaments, and osteochondral surfaces.Study Design:Cohort study (diagnosis); Level of evidence, 2.Methods:MRI examinations without intra-articular contrast were performed on 379 patients for knee pathologies over a 4-year period. The MRI examinations were done using a 0.2-tesla scanner utilizing a dedicated knee coil and read by 1 of 3 board-certified, musculoskeletal fellowship–trained radiologists. Within a mean time of 50 days after MRI, all patients underwent knee arthroscopy performed by 1 of 2 sports fellowship–trained orthopaedic surgeons. Operative notes from the knee arthroscopies were then reviewed by a single independent observer, and the intraoperative findings were compared with the MRI reports.Results:For medial meniscus tears, the sensitivity, specificity, positive predictive value, and negative predictive value were 83%, 81%, 89%, and 71%, respectively. For lateral meniscus tears, the values were 51%, 93%, 84%, and 73%, respectively. For anterior cruciate ligament (ACL) tears, the values were 85%, 94%, 69%, and 97%, respectively. For osteochondral lesions, the values were 8%, 99%, 29%, and 94%, respectively. For posterior cruciate ligament (PCL) tears, the specificity and negative predictive value were 99% and 100%, respectively.Conclusion:Low-field MRI was an accurate tool for evaluation of medial meniscus and ACL tears. However, within the study population, it is not as effective in diagnosing lateral meniscus tears and showed a poor ability to detect osteochondral lesions. More information is needed to properly assess its ability to diagnose PCL tears.

FDTD Analysis of a Radiofrequency Knee Coil for Low-Field MRI: Sample-Induced Resistance and Decoupling Evaluation

Magnetic resonance imaging (MRI) using high static field (>3T) generates high-quality images, thanks to high homogeneity in transmission as well as high signal-to-noise ratio (SNR) in reception. On the other hand, biological effects are proportional to the magnetic field strength and moreover the diagnostic accuracy is not always linked to high-quality imaging. For these reasons, the interest in low-field imaging becomes greater, also because of cheaper setting, greater patients comfort and more safety profile. In simple cases, as for surface coil, the coil performance is evaluated using classical electromagnetic theory, but for more complex geometry and in presence of a sample, is more difficult to evaluate the solution and often is necessary to follow a trial-and-error approach. Numerical methods represent a solution to this problem. In this work, we performed numerical simulation on a two-channel knee coil for low-field (0.5 T) MRI scanner. We are interested in seeing the effect of a sample placed inside the coil on the sample-induced resistance and decoupling between channels. In particular, we observe how the position of the sample inside the channel influences the resistance value and for performing this we compared an innovative method based on the exponential fitting on voltage oscillation damping with a validated method (estimation using quality factor). Finally, for the complete coil, the scatter parameters were calculated in loaded and unloaded conditions.

Lumbar Modic Changes—A Comparison Between Findings at Low- and High-Field Magnetic Resonance Imaging

A cross-sectional observational study. To investigate whether there is a difference in findings of lumbar Modic changes in low-field (0.3 T) magnetic resonance imaging (MRI) compared with high-field (1.5 T). It is a challenge to give patients with low back pain a specific diagnosis. Modic changes as seen on MRI have been reported to be a possible source of pain. However, it is unclear whether the diagnosis is independent on the field strength. Twenty patients with Modic changes, 11 women and 9 men (mean age, 53.6 yr; range, 29-81 yr), with or without sciatica, seen in a Danish outpatient low back pain clinic were included. All patients obtained MRI scans on both a high-field and a low-field MRI scanner. Two radiologists evaluated all lumbar endplates independently, using a standardized evaluation protocol. Kappa statistics were used to analyze the interobserver reproducibility. We used paired t test to analyze the difference between low- and high-field MRI. The total number of Modic changes diagnosed with high-field MRI was significantly higher than that with low-field MRI. However, 3 to 4 times as many Modic type 1 changes were found with low-field MRI compared with high-field MRI. Contrarily, with high-field MRI type 2 changes were diagnosed twice as often. There was a significant difference between low- and high-field MRI regarding the overall prevalence of any Modic change, but this had opposite directions for types 1 and 2: type 2 dominated in high field and conversely in high field [corrected]. The type of MRI unit should be taken into consideration when diagnosing patients with Modic changes

Validity of upper airway assessment in children:A clinical, cephalometric, and MRI study

To test the hypothesis that the capability of two-dimensional lateral cephalogram in recognizing pharyngeal obstruction is poor compared with the capability of three-dimensional magnetic resonance imaging (MRI) and clinical observation of tonsillar size. The study participants were 36 prepubertal children (19 male, 17 female; mean age 7.3 ± 1.43 years, range 4.8-9.8 years) with sleep-disordered breathing diagnosed by nocturnal polygraphy. Pharyngeal airway was imaged with a low-field open-configuration MRI scanner. Tonsillar size was clinically determined and lateral skull radiographs were taken and measured. Pearson correlation coefficients were calculated between the clinical, cephalometric, and MRI variables. Nasopharyngeal and retropalatal cephalometric variables had a significant positive correlation with the MRI findings. Both techniques showed the narrowest measurement to be located in the retropalatal region. Clinical assessment of tonsillar size correlated inversely with MRI findings such as minimal retropalatal cross-sectional airway area (P = .000), minimal retroglossal cross-sectional airway area (P = .015), and intertonsillar airway width (P = .000). Cephalometric soft palate and tonsillar area correlated with clinical tonsillar size (P = .001). The hypothesis is rejected. The findings confirm that the lateral cephalogram is a valid method for measuring dimensions of the nasopharyngeal and retropalatal region. When evaluating oropharyngeal size, clinical assessment of tonsillar size is a relatively reliable method.

USEFULNESS OF INTRAOPERATIVE ULTRA LOW-FIELD MAGNETIC RESONANCE IMAGING IN GLIOMA SURGERY

The aim of this study was to demonstrate the usefulness of a mobile, intraoperative 0.15-T magnetic resonance imaging (MRI) scanner in glioma surgery. We analyzed our prospectively collected database of patients with glial tumors who underwent tumor resection with the use of an intraoperative ultra low-field MRI scanner (PoleStar N-20; Odin Medical Technologies, Yokneam, Israel/Medtronic, Louisville, CO). Sixty-three patients with World Health Organization Grade II to IV tumors were included in the study. All patients were subjected to postoperative 1.5-T imaging to confirm the extent of resection. Intraoperative image quality was sufficient for navigation and resection control in both high- and low-grade tumors. Primarily enhancing tumors were best detected on T1-weighted imaging, whereas fluid-attenuated inversion recovery sequences proved best for nonenhancing tumors. Intraoperative resection control led to further tumor resection in 12 (28.6%) of 42 patients with contrast-enhancing tumors and in 10 (47.6%) of 21 patients with noncontrast-enhancing tumors. In contrast-enhancing tumors, further resection led to an increased rate of complete tumor resection (71.2 versus 52.4%), and the surgical goal of gross total removal or subtotal resection was achieved in all cases (100.0%). In patients with noncontrast-enhancing tumors, the surgical goal was achieved in 19 (90.5%) of 21 cases, as intraoperative MRI findings were inconsistent with postoperative high-field imaging in 2 cases. The use of the PoleStar N-20 intraoperative ultra low-field MRI scanner helps to evaluate the extent of resection in glioma surgery. Further tumor resection after intraoperative scanning leads to an increased rate of complete tumor resection, especially in patients with contrast-enhancing tumors. However, in noncontrast- enhancing tumors, the intraoperative visualization of a complete resection seems less specific, when compared with postoperative 1.5-T MRI.