Comparison of low field (0.2T) and high field (1.5T) MR imaging in the differentiation of torned from intact menisci

Low-Field Magnetic Resonance Imaging: Its History and Renaissance

ABSTRACT

Low-field magnetic resonance imaging (MRI) systems have seen a renaissance recently due to improvements in technology (both hardware and software). Originally, the performance of low-field MRI systems was rated lower than their actual clinical usefulness, and they were viewed as low-cost but poorly performing systems. However, various applications similar to high-field MRI systems (1.5 T and 3 T) have gradually become possible, culminating with high-performance low-field MRI systems and their adaptations now being proposed that have unique advantages over high-field MRI systems in various aspects. This review article describes the physical characteristics of low-field MRI systems and presents both their advantages and disadvantages for clinical use (past to present), along with their cutting-edge clinical applications.

Pros and cons of low-field magnetic resonance imaging in veterinary practice

Low-field (LF) (0.2-0.4T) magnetic resonance (MR) imaging predominates in veterinary practice. Advantages of LF MR include reduced costs, better patient access, and greater safety. High quality examinations can be achieved using appropriate protocols and investing more scanning time than with high-field (HF) systems. The main disadvantage of LF MR is the reduced signal to noise ratio compared with HF systems. LF MR protocols for small animal brain and spine imaging are described.

The effect of sequence selection and field strength on detection of osteochondral defects in the metacarpophalangeal joint

Six cadaver forelimbs were imaged in two high-field magnetic resonance (MR) systems and one low-field MR system following the creation of osteochondral defects on the palmar distal aspect of the third metacarpal bone. The following sequences were performed using all three systems: proton density (PD) turbo spin echo, T2* gradient echo (GRE), T2-weighted fast spin echo, and short tau inversion recovery. In addition, 3D T1 GRE sagittal standard and motion insensitive sequences were obtained using the low-field system. PD fat saturated and 3D T1-weighted spoiled GRE images with and without fat suppression were acquired with the high-field systems. Lesions were measured and assigned a confidence score. The images obtained using high-field systems (1.0 and 1.5 T) more accurately represented the osteochondral defects when compared with low-field system (0.27 T) images. The largest difference was observed when evaluating articular cartilage defects, which were not identified on the low-field images. Sequence selection affected the appearance of the lesions. On all systems the turbo and fast spin echo sequences more accurately represented the lesion size and shape when compared with the GRE sequences. The T1 GRE sequence is the only sequence that appears to allow visualization of the articular cartilage on the low-field images, but is limited in providing adequate cartilage visualization. Confidence scores were greater on the high-field systems when compared with the low-field system.

High-resolution magnetic resonance imaging and conventional magnetic resonance imaging on a standard field-strength magnetic resonance system compared to arthroscopy in patients with suspected meniscal tears

RATIONALE AND OBJECTIVES

We sought to evaluate the diagnostic performance of high-resolution magnetic resonance imaging (MRI) and conventional MRI of the knee on a standard-field-strength MRI system compared to arthroscopic findings in patients with suspected meniscal tears.

MATERIALS AND METHODS

Forty-two patients (20 women, 22 men), referred from the department of trauma surgery, with suspected medial meniscal tears and planned arthroscopy of the knee joint were included in the study. MRI was performed on a 1.0-T MRI scanner with two different protocols: (1) conventional MRI using a circular, polarized knee coil (coil diameter: 17 cm) with a sagittal dual fast spin-echo sequence (repetition time [TR]: 2500 ms; echo time [TE]: first, shortest, second, 120 ms; turbo spin echo [TSE] factor: 12; field of view: 180 mm; matrix: 256 x 512; scan percentage: 100; slice thickness: 3 mm) or (2) high-resolution MRI with a surface dual-loop coil of the medial knee compartment (temporomandibular joint, coil diameter: 8 cm) with a sagittal dual fast spin-echo sequence (TR: 2400 ms; TE: first, shortest; second, 120 ms; TSE factor: 12; field of view: 120 mm; matrix: 512 x 512; slice thickness: 2 mm). The menisci were evaluated on the basis of an adapted score (0 = normal meniscus, 1 = intrameniscal, T2-weighted hyperintense signal, 2 = discontinuity of the surface, 3 = fragmentation). Lesions that received a score of 2 or 3 were graded as meniscal tears. The MRI results were compared to the arthroscopic reports, which represented the gold standard, and the sensitivity of both protocols in detecting a meniscal tear was determined.

RESULTS

Of the 42 patients included in the study, 25 (11 women and 14 men) underwent arthroscopy and all demonstrated a meniscal tear. A meniscal tear was correctly diagnosed in 76% of cases with conventional MRI and in 88% of cases with high-resolution MRI (P = .0087).

CONCLUSION

High-resolution MRI, using a surface dual-loop coil and specific sequences, which can be performed on every standard-field-strength MRI scanner, is able to significantly improve diagnostic performance for the detection of a meniscal tear of the knee joint.

Are early MRI findings correlated with long-lasting symptoms following whiplash injury? A prospective trial with 1-year follow-up

Neck pain is the cardinal symptom following whiplash injuries. The trauma mechanism could theoretically lead to both soft tissue and bone injury that could be visualised by means of MRI. From previous quite small trials it seems that MRI does not demonstrate significant tissue damage. Large prospectively followed cohorts are needed to identify possible clinically relevant MRI findings. The objective of this trial was to evaluate (1) the predictive value of cervical MRI after whiplash injuries and (2) the value of repeating MRI examinations after 3 months including sequences with flexion and extension of the cervical spine. Participants were included after rear-end or frontal car collisions. Patients with fractures or dislocations diagnosed by standard procedures at the emergency unit were not included. MRI scans of the cervical spine were performed at baseline and repeated after 3 months. Clinical follow-ups were performed after 3 and 12 months. Outcome parameters were neck pain, headache, neck disability and working ability. A total of 178 participants had a cervical MRI scan on average 13 days after the injury. Traumatic findings were observed in seven participants. Signs of disc degeneration were common and most frequent at the C5-6 and C6-7 levels. Findings were not associated with outcome after 3 or 12 months. The population had no considerable neck trouble prior to the whiplash injury and the non-traumatic findings represent findings to be expected in the background population. Trauma-related MRI findings are rare in a whiplash population screened for serious injuries in the emergency unit and not related to a specific symptomatology. Also, pre-existing degeneration is not associated with prognosis.

MR imaging of the meniscus: review, current trends, and clinical implications

MR imaging is the preferred imaging modality for evaluating the meniscus. Overall, when strict criteria are followed, it is accurate in diagnosing meniscal tears in patients who have not had prior meniscal surgery. However, an accurate interpretation requires a through knowledge of the normal meniscal anatomy, common meniscal variants, and common diagnostic pitfalls. In this article, the author emphasizes the importance of describing meniscal tears properly and discusses treatment options. Diagnosing a recurrent tear is more complicated in patients who have had prior partial meniscal resection or repair, and the use of MR arthrography in this group of patients is discussed. Recent developments in areas such as 3 T and parallel imaging offer promise for accurate meniscal evaluation with even shorter scan times.

MR Imaging of the Meniscus: Review, Current Trends, and Clinical Implications

MR imaging is the preferred imaging modality for evaluating the meniscus. Overall, when strict criteria are followed, it is accurate in diagnosing meniscal tears in patients who have not had prior meniscal surgery. However, an accurate interpretation requires a through knowledge of the normal meniscal anatomy, common meniscal variants, and common diagnostic pitfalls. In this article, the author emphasizes the importance of describing meniscal tears properly and discusses treatment options. Diagnosing a recurrent tear is more complicated in patients who have had prior partial meniscal resection or repair, and the use of MR arthrography in this group of patients is discussed. Recent developments in areas such as 3 T and parallel imaging offer promise for accurate meniscal evaluation with even shorter scan times.

Musculoskeletal Imaging at 3T: Current Techniques and Future Applications

MSK MR imaging applications are making the transition rapidly from 1.5T to 3T. Initial experience in the knee suggests that the higher SNR provides technical improvement in routine clinical imaging with the potential for greater accuracy in the diagnosis of articular cartilage injury. Similarly, initial experience with 3T MR imaging in the evaluation of the hip and small joints of the hand and wrist has been positive. In other joints, clinical development has been limited by the lack of availability of dedicated surface coils, and sensitivity of 3TMR imaging to artifact. The clinical impact of this technology remains uncertain because no published controlled clinical trial has evaluated the impact of 3T MR imaging on diagnostic outcomes. In addition to clinical application, 3T MR imaging has an important role for furthering translational research in MSK diseases through the development of new molecular and functional MR imaging techniques.

Computer-aided quantification of focal cartilage lesions using MRI: accuracy and initial arthroscopic comparison

OBJECTIVE

The purpose of the study was to validate a Gradient Peak Method (GPM) by evaluating its accuracy and consistency at different magnetic field strengths. The GPM using magnetic resonance imaging (MRI) was previously proposed to quantitatively assess the morphology of focal cartilage lesions, and its feasibility was demonstrated.

METHODS

GPM quantifies the morphologic properties of cartilage lesions based on their three-dimensional geometry. Twenty-two conical and cylindrical lesions were surgically created on fresh porcine knees, and the results obtained by GPM were compared with manually measured lesion dimensions. Another 15 focal lesions of various shapes were created and scanned, and the quantification results were compared at 1.5 Tesla and 3 Tesla. Additionally, cartilage lesions in three patients were scanned, quantified by GPM, and compared with arthroscopic visualization and measurements.

RESULTS

The average absolute errors of GPM (depth: < or =0.4mm; diameter: < or =1.4mm) were within twice the in-plane resolution in depth estimates and within the slice thickness in diameter estimates. Analysis also suggested that the quantifications of GPM using 1.5 Tesla and 3 Tesla data were not statistically different. Moreover, the GPM results were shown to be consistent with the lesion measurements obtained arthroscopically.

CONCLUSIONS

The GPM using MRI provides estimates of lesion thickness, depth, diameter, and area. With this validation, the method can be potentially used as an auxiliary tool to help radiologists and physicians assess cartilage lesions quantitatively and monitor disease progression.

High- Versus Low-Field MR Imaging

The role of MR imaging as a noninvasive technique in the detection and evaluation of musculoskeletal diseases is unquestionable. Most of the studies reported in the literature are based on high-field MR imaging. Initial studies performed with low-field-strength have reported unsatisfactory results in the assessment of the musculoskeletal system. Recent improvements, however, have generated a renewed interest in low-field-strength MR imaging. This article presents the principal applications and results published in the literature.

Comparison of multiple sclerosis lesions at 1.5 and 3.0 Tesla

OBJECTIVE

To evaluate the relative sensitivity of MR scanning for multiple sclerosis (MS) at 1.5 Tesla (T) and 3.0 T using identical acquisition conditions, as is typical of multicenter clinical trials.

METHODS

Twenty-five subjects with MS were scanned at 1.5 T and 3.0 T using fast spin echo, and T(1)-weighted SPGR with and without gadolinium contrast injections. Image data, blinded to field strength, were analyzed using automated segmentation and lesion counting.

RESULTS

Relative to scanning at 1.5 T, the 3.0 T scans showed a 21% increase in the number of detected contrast enhancing lesions, a 30% increase in enhancing lesion volume and a 10% increase in total lesion volume.

DISCUSSION

The improved detection ability using high-field MR imaging is prominent even when sequence parameters are optimized around the midfield units. Multicenter trials using both 1.5 T and 3.0 T instruments may be affected by these sensitivity differences.