Spin locking for magnetic resonance imaging with application to human breast

Santyr, Giles; Henkelman, R. Mark; Bronskill, Michael

doi:10.1002/mrm.1910120104

Cited by 115 publications

(97 citation statements)

References 17 publications

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“…T 1r studies in solution-state NMR have been reviewed extensively (166)(167)(168). There has been a considerable amount of work on biological tissues using T 1r -spectroscopy and imaging dealing with tumors, muscle, myocardium, blood flow and cartilage (26,165,(169)(170)(171)(172)(173)(174)(175)(176)(177)(178)(179).…”

Section: T 1r Mrimentioning

confidence: 99%

Sodium and T_1ρ MRI for molecular and diagnostic imaging of articular cartilage

et al. 2006

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In this article, both sodium magnetic resonance (MR) and T 1r relaxation mapping aimed at measuring molecular changes in cartilage for the diagnostic imaging of osteoarthritis are reviewed. First, an introduction to structure of cartilage, its degeneration in osteoarthritis (OA) and an outline of diagnostic imaging methods in quantifying molecular changes and early diagnostic aspects of cartilage degeneration are described. The sodium MRI section begins with a brief overview of the theory of sodium NMR of biological tissues and is followed by a section on multiple quantum filters that can be used to quantify both bi-exponential relaxation and residual quadrupolar interaction. Specifically, (i) the rationale behind the use of sodium MRI in quantifying proteoglycan (PG) changes, (ii) validation studies using biochemical assays, (iii) studies on human OA specimens, (iv) results on animal models and (v) clinical imaging protocols are reviewed. Results demonstrating the feasibility of quantifying PG in OA patients and comparison with that in healthy subjects are also presented. The section concludes with the discussion of advantages and potential issues with sodium MRI and the impact of new technological advancements (e.g. ultra-high field scanners and parallel imaging methods). In the theory section on T 1r , a brief description of (i) principles of measuring T 1r relaxation, (ii) pulse sequences for computing T 1r relaxation maps, (iii) issues regarding radio frequency power deposition, (iv) mechanisms that contribute to T 1r in biological tissues and (v) effects of exchange and dipolar interaction on T 1r dispersion are discussed. Correlation of T 1r relaxation rate with macromolecular content and biomechanical properties in cartilage specimens subjected to trypsin and cytokineinduced glycosaminoglycan depletion and validation against biochemical assay and histopathology are presented. Experimental T 1r data from osteoarthritic specimens, animal models, healthy human subjects and as well from osteoarthritic patients are provided. The current status of T 1r relaxation mapping of cartilage and future directions is also discussed. Copyright # 2006 John Wiley & Sons, Ltd. KEYWORDS: cartilage; arthritis; spin-lock; T1rho; sodium; MRI OSTEOARTHRITIS Osteoarthritis (OA) affects more than half of the population above the age of 65 (1,2) and has a significant negative impact on the quality of life of elderly individuals (3). The economic costs in the USA from OA have been estimated to be more than 1% of the gross domestic product (4). OA is now increasingly viewed as a metabolically active joint disorder of diverse etiologies. The biochemistry of the disease is characterized by the following changes in cartilage: reduced proteoglycan (PG) concentration, possible changes in the size of collagen fibril and aggregation of PG, increased water content and increased rate of synthesis and degradation of matrix macromolecules. The earliest changes in the cartilage due to OA result in a partial breakdown in the proteoglyc...

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Section: T 1r Mrimentioning

confidence: 99%

Sodium and T_1ρ MRI for molecular and diagnostic imaging of articular cartilage

et al. 2006

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“…A two-dimensional gradient-echo localizer image was acquired for slice positioning and to facilitate location of arteries and veins during data processing. The imaging parameters were TE/TR ϭ 3.5/10 msec, flip angle ϭ 90°, these values were chosen to enhance the signal from flowing blood, with an FOV of 180 ϫ 180 mm 2 , and a slice thickness of 3 mm. T 1 -weighted images were acquired using SLEPI at eight different TSL times (10,20,30,40,50,60,80, and 100 msec) of the same slice location, FOV, and thickness as the localizer image.…”

Section: Estimation Of T 1 In Bloodmentioning

confidence: 99%

“…The sensitivity of T 1 to low-frequency interactions facilitates the study of biological tissues in a manner that is unattainable by conventional T 1 -and T 2 -based MR methods. Consequently, T 1 MRI has been used to investigate a variety of tissues such as breast, brain, and cartilage (1)(2)(3).…”

mentioning

confidence: 99%

A pulse sequence for rapid in vivo spin‐locked MRI

Borthakur

Hulvershorn

Gualtieri

et al. 2006

Magnetic Resonance Imaging

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Purpose: To develop a novel pulse sequence called spinlocked echo planar imaging (EPI), or (SLEPI), to perform rapid T 1 -weighted MRI. Materials and Methods:SLEPI images were used to calculate T 1 maps in two healthy volunteers imaged on a 1.5-T Sonata Siemens MRI scanner. The head and extremity coils were used for imaging the brain and blood in the popliteal artery, respectively.Results: SLEPI-measured T 1 was 83 msec and 103 msec in white (WM) and gray matter (GM), respectively, 584 msec in cerebrospinal fluid (CSF), and was similar to values obtained with the less time-efficient sequence based on a turbo spin-echo readout. T 1 was 183 msec in arterial blood at a spin-lock (SL) amplitude of 500 Hz. Conclusion:We demonstrate the feasibility of the SLEPI pulse sequence to perform rapid T 1 MRI. The sequence produced images of higher quality than a gradient-echo EPI sequence for the same contrast evolution times. We also discuss applications and limitations of the pulse sequence. T 1⌹ OR "SPIN-LOCKED" MRI produces contrast unlike conventional T 1 -or T 2 -weighted images. Spin-locking is achieved by the application of a low power on-resonance radiofrequency (RF) pulse to the magnetization in the transverse plane. The resulting MR signal decays with a time constant T 1 and is dominated by processes that occur with a correlation time, c , that is related to the amplitude of the spin-lock (SL) pulse (␥B 1 /2 ), which typically ranges from zero to a few kilohertz. T 1 is commonly referred to as the longitudinal relaxation time constant in the rotating frame. In biological tissues, T 1 increases with higher B 1 and approaches T 2 , the spin-spin relaxation time constant, as the amplitude of the SL pulse is reduced to zero. The sensitivity of T 1 to low-frequency interactions facilitates the study of biological tissues in a manner that is unattainable by conventional T 1 -and T 2 -based MR methods. Consequently, T 1 MRI has been used to investigate a variety of tissues such as breast, brain, and cartilage (1-3).Recently, T 1 imaging has been employed to measure blood flow and oxygen metabolism and the effect of tracers such as H 2 17 O (4,5). These studies were performed using standard spin-echo, turbo (fast) spinecho, or gradient-echo-based pulse sequences. There is substantial evidence demonstrating that the T 1 relaxation time parameter is sensitive to the early detection of cerebral ischemia (6 -8). Kettunen et al (9) revealed a linear dependence of T 1 as a function of oxygen saturation in experiments performed in vitro. Dynamic studies such as these and others that involve imaging of flowing spins such as that of blood would benefit from a fast T 1 imaging technique that is able to acquire images in the order of tens of milliseconds.A method of rapid image acquisition is the echo planar imaging (EPI) technique (10,11). In its conventional form, the EPI pulse sequence consists of an excitation pulse that is followed by a train of gradientechoes within a single pulse repetition time (TR), and is capable of generat...

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“…For an on-resonance RF field with the given input parameters, the saturated magnetization, M sat , is described by Eq. [2] with the equilibrium term M equilibrium sat , coefficients c 1 , c 2 , c 3 , and with constant terms 1 , 2 , 3 . ) and is nutated into the y-axis by the initial hard 90°along the x-axis.…”

Section: Saturation Modelmentioning

confidence: 99%

“…The equilibrium term is identical to the steady-state equation for on-resonance saturation (Eq. [3]) (23).…”

Section: Saturation Modelmentioning

confidence: 99%

Pulse sequence for multislice T_1ρ‐weighted MRI

Wheaton

Borthakur

Charagundla

et al. 2004

Magnetic Resonance in Med

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A 2D multislice spin-lock (MS-SL) MR pulse sequence is presented for rapid volumetric T 1 -weighted imaging. Image quality is compared with T 1 -weighted data collected using a singleslice (SS) SL sequence and T 2 -weighted data from a standard MS spin-echo (SE) sequence. Saturation of longitudinal magnetization by the application of nonselective SL pulses is experimentally measured and theoretically modeled as T 2 decay. The saturation data is used to correct the image data as a function of the SL pulse duration to make quantitative measurements of T 1 . Measurements of T 1 using the saturation-corrected MS-SL data are nearly identical to those measured using an SS-SL sequence. The MS-SL sequence produces quantitative T 1 maps of an entire sample volume with the high-SNR advantages conferred by SE-based sequences.Magn In this study, spin-lock (SL) MRI was used to generate an alternative contrast to conventional proton density, T 1 -, or T 2 -weighted MRI methods. In SL-MRI, a long-duration, low-power SL pulse is applied to "lock" the spins in the transverse plane. During the SL pulse, the transverse magnetization decays according to T 1 , the spin-lattice relaxation in the rotating frame of reference. The amplitude of the SL pulse is commonly referenced in terms of the nutation frequency (␥B 1 ), which is typically in the range of a few hundred hertz to a few kilohertz. T 1 relaxation phenomena are sensitive to physicochemical processes with inverse correlation times on the order of the nutation frequency of the SL pulse. By setting the amplitude of the SL pulse to coincide with the frequency of the molecular processes of interest, the signal from the SL-MRI sequence becomes heavily weighted by the T 1 parameter according to Eq. [1], where TSL is the SL pulse duration, and S is the signal intensity as a function of TSL.By acquiring a series of T 1 -weighted images at varying TSL durations with constant SL pulse amplitude, and using Eq.[1], the T 1 parameter can be measured on a pixelby-pixel basis using linear regression to create a quantitative spatial map of T 1 values. SL pulse sequences may be applicable for imaging multiple systems, such as muscle (1,2), breast (3), liver (4), brain (5,6), and tumors (7,8). T 1 relaxation has been used as an indicator of proteoglycan content in articular cartilage, and is being developed as a diagnostic tool for the detection of osteoarthritis (9 -12). In addition, T 1 -weighted MRI of H 2 17O was recently used to measure cerebral and tumor perfusion (13,14). The sensitivity of T 1 to a variety of physiological parameters has also been demonstrated (15).T 1 weighting can be added to most MRI sequences by including an SL pulse cluster at the beginning of the pulse sequence. The magnetization thereby becomes "T 1 -prepared" and results in a T 1 -weighted signal. A 2D singleslice (SS) SL sequence based on a spin-echo (SE) sequence has been successfully implemented to produce a single 2D T 1 -weighted slice (16). The schematic for the SS-SL sequence is shown in Fig. 1. The nut...

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Spin locking for magnetic resonance imaging with application to human breast

Cited by 115 publications

References 17 publications

Sodium and T_1ρ MRI for molecular and diagnostic imaging of articular cartilage

Sodium and T_1ρ MRI for molecular and diagnostic imaging of articular cartilage

A pulse sequence for rapid in vivo spin‐locked MRI

Pulse sequence for multislice T_1ρ‐weighted MRI

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Spin locking for magnetic resonance imaging with application to human breast

Cited by 115 publications

References 17 publications

Sodium and T1ρ MRI for molecular and diagnostic imaging of articular cartilage

Sodium and T1ρ MRI for molecular and diagnostic imaging of articular cartilage

A pulse sequence for rapid in vivo spin‐locked MRI

Pulse sequence for multislice T1ρ‐weighted MRI

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Product

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Sodium and T_1ρ MRI for molecular and diagnostic imaging of articular cartilage

Sodium and T_1ρ MRI for molecular and diagnostic imaging of articular cartilage

Pulse sequence for multislice T_1ρ‐weighted MRI