Quadrature radio frequency coil for magnetic resonance imaging of the wrist at 4T

Zailaa, Ali; Vegh, Viktor; Maillet, Donald; Strudwick, Mark

doi:10.1002/cmr.b.20146

Cited by 4 publications

(3 citation statements)

References 13 publications

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“…Outcome Measures MRI scans of the affected wrist (or most affected wrist in case of bilateral mild or moderate CTS) were performed using a purpose built transmit-receive wrist coil on a Bruker Medspec 4Tesla (4T) MR scanner 27 28 (TR 14.29 TE 3.92; matrix 192 Ã 96, NSA 1, flip angle 30 degrees, water excitation)] were applied to generate high resolution T1 and T2 axial images. These images were reconstructed post-hoc in other planes for analysis.…”

Section: Interventionmentioning

confidence: 99%

Effect of splinting and exercise on intraneural edema of the median nerve in carpal tunnel syndrome—an MRI study to reveal therapeutic mechanisms

Schmid

Elliott

Strudwick

et al. 2012

Journal Orthopaedic Research

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Splinting and nerve and tendon gliding exercises are commonly used to treat carpal tunnel syndrome (CTS). It has been postulated that both modalities reduce intraneural edema. To test this hypothesis, 20 patients with mild to moderate CTS were randomly allocated to either night splinting or a home program of nerve and tendon gliding exercises. Magnetic resonance images of the wrist were taken at baseline, immediately after 10 min of splinting or exercise, and following 1 week of intervention. Primary outcome measures were signal intensity of the median nerve at the wrist as a measure of intraneural edema and palmar bowing of the carpal ligament. Secondary outcome measures were changes in symptom severity and function. Following 1 week of intervention, but not immediately after 10 min, signal intensity of the median nerve was reduced by $11% at the radioulnar level for both interventions (p ¼ 0.03). This was accompanied by a mild improvement in symptoms and function (p < 0.004). A similar reduction in signal intensity is not observed in patients who only receive advice to remain active. No changes in signal intensity were identified further distally (p > 0.28). Ligament bowing remained unchanged (p > 0.08). Intraneural edema reduction is a likely therapeutic mechanism of splinting and exercise. Keywords: MRI; nerve and tendon gliding exercises; splinting; carpal tunnel syndrome; neurodynamics Carpal tunnel syndrome (CTS) is a peripheral neuropathy at the level of the wrist. Despite considerable efforts, the pathophysiology of CTS is not yet fully understood. 1 There is however a well-established link between an elevated pressure in the carpal tunnel and the development of CTS. 2,3 When the pressure on a peripheral nerve is experimentally increased, a reduction of intraneural microcirculation occurs with subsequent breakdown of the blood nerve barrier and the formation of intraneural and extraneural edema. 4 In CTS, swelling of the median nerve has been identified intra-operatively, 5,6 with ultrasound imaging 7 and with conventional magnetic resonance imaging (MRI). 8,9 If present for prolonged periods, intraneural edema may lead to potentially irreversible fibrotic changes. 4 These fibrotic changes are present in patients with severe CTS. 9 Edema reduction to prevent progression to a fibrotic stage is therefore a plausible target in the management of patients with mild to moderate CTS.Besides advice, splinting and nerve and tendon gliding exercises are the most frequently performed noninvasive treatment modalities for CTS. 10 The beneficial effect of night splinting in a neutral wrist position is commonly attributed to the avoidance of end-range positions associated with high carpal tunnel pressures. 11,12 Maintenance of a neutral wrist position is believed to promote adequate blood circulation with a subsequent reduction of edema. 13 Although further research is required, recent systematic reviews indicate that conservative management with nerve and tendon gliding exercises may be beneficial for patie...

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Section: Interventionmentioning

confidence: 99%

Effect of splinting and exercise on intraneural edema of the median nerve in carpal tunnel syndrome—an MRI study to reveal therapeutic mechanisms

Schmid

Elliott

Strudwick

et al. 2012

Journal Orthopaedic Research

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“…The idea of simultaneously using a geometrically decoupled combination of perpendicular loops has been explored previously by multiple research groups. For example, a pair of such loops can be used as a quadrature Tx coil or as an Rx‐only coil for SNR improvement . Work by Maunder et al proposed the use of a combination of a surface loop and two perpendicular orthogonal vertical loops as an element of an Rx‐only, so‐called composite, array.…”

Section: Introductionmentioning

confidence: 99%

Combination of surface and ‘vertical’ loop elements improves receive performance of a human head transceiver array at 9.4 T

et al. 2017

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Ultra-high-field (UHF, ≥7 T) human magnetic resonance imaging (MRI) provides undisputed advantages over low-field MRI (≤3 T), but its development remains challenging because of numerous technical issues, including the low efficiency of transmit (Tx) radiofrequency (RF) coils caused by the increase in tissue power deposition with frequency. Tight-fit human head transceiver (TxRx) arrays improve Tx efficiency in comparison with Tx-only arrays, which are larger in order to fit multi-channel receive (Rx)-only arrays inside. A drawback of the TxRx design is that the number of elements in an array is limited by the number of available high-power RF Tx channels (commonly 8 or 16), which is not sufficient for optimal Rx performance. In this work, as a proof of concept, we developed a method for increasing the number of Rx elements in a human head TxRx surface loop array without the need to move the loops away from a sample, which compromises the array Tx performance. We designed and constructed a prototype 16-channel tight-fit array, which consists of eight TxRx surface loops placed on a cylindrical holder circumscribing a head, and eight Rx-only vertical loops positioned along the central axis (parallel to the magnetic field B ) of each TxRx loop, perpendicular to its surface. We demonstrated both experimentally and numerically that the addition of the vertical loops has no measurable effect on the Tx efficiency of the array. An increase in the maximum local specific absorption rate (SAR), evaluated using two human head voxel models (Duke and Ella), measured 3.4% or less. At the same time, the 16-element array provided 30% improvement of central signal-to-noise ratio (SNR) in vivo relative to a surface loop eight-element array. The novel array design also demonstrated an improvement in the parallel Rx performance in the transversal plane. Thus, using this method, both the Rx and Tx performance of the human head array can be optimized simultaneously.

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“…The reconstructed images, saved as DICOM (digital imaging and communications in medicine) files, were used to calculate the SNR with our in-house MATLAB program. We have used this program previously in a wrist imaging study, to calculate SNR of MR images in accordance with the international standards [18]. Basically, the program separates the foreground (sample) from the background (noise) and this information is used to compute the SNR map of the image according to:…”

Section: Measuring Signal and Quantifying Susceptibilitymentioning

confidence: 99%

High-field magnetic resonance imaging using solenoid radiofrequency coils

Vegh

Gläser

Maillet

et al. 2012

Magnetic Resonance Imaging

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Quadrature radio frequency coil for magnetic resonance imaging of the wrist at 4T

Cited by 4 publications

References 13 publications

Effect of splinting and exercise on intraneural edema of the median nerve in carpal tunnel syndrome—an MRI study to reveal therapeutic mechanisms

Effect of splinting and exercise on intraneural edema of the median nerve in carpal tunnel syndrome—an MRI study to reveal therapeutic mechanisms

Combination of surface and ‘vertical’ loop elements improves receive performance of a human head transceiver array at 9.4 T

High-field magnetic resonance imaging using solenoid radiofrequency coils

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