Magnetic resonance imaging of cortical bone with ultrashort TE pulse sequences

doi:10.1016/j.mri.2005.02.017

Magnetic Resonance Imaging

Volume 23, Issue 5, June 2005, Pages 611-618

https://doi.org/10.1016/j.mri.2005.02.017 Get rights and content

Abstract

Purpose

Normal adult cortical bone has a very short T₂ and characteristically produces no signal with pulse sequence echo times (TEs) routinely used in clinical practice. We wished to determine whether it was possible to use ultrashort TE (UTE) pulse sequences to detect signal from cortical bone in human subjects and use this signal to characterise this tissue.

Subjects and Methods

Seven volunteers and 10 patients were examined using ultrashort TE pulse sequences (TE=0.07 or 0.08 ms). Short and long inversion as well as fat suppression pulses were used as preparation pulses. Later echo images were also obtained as well as difference images produced by subtracting a later echo image from a first echo image. Saturation pulses were used for T₁ measurement and sequences with progressively increasing TEs for T₂* measurement. Intravenous gadodiamide was administered to four subjects.

Results

Signal in cortical bone was detected with UTE sequences in children, normal adults and patients. This signal was usually made more obvious by subtracting a later echo image from the first provided that the signal-to-noise ratio was sufficiently high.

Normal mean adult T₁s ranged from 140 to 260 ms, and mean T₂*s ranged from 0.42 to 0.50 ms. T₁ increased significantly with age (P<.01).

Increased signal was observed after contrast enhancement in the normal volunteer and the three patients to whom it was administered.

Reduction in signal from short T₂ components was seen in acute fractures, and increase in signal in these components was seen with new bone formation after fracture malunion. In a case of osteoporosis, bone cross-sectional area and signal level appeared reduced.

Conclusion

Signal can be detected from normal and abnormal cortical bone with UTE pulse sequences, and this can be used to measure its T₁ and T₂* as well as observe contrast enhancement. Difference images are of value in increasing the conspicuity of cortical bone and observing abnormalities in disease.

Introduction

With virtually all forms of proton imaging used in clinical practice normal adult cortical bone has a short T₂ and shows no signal. This lack of signal provides a constant background against which abnormalities can be recognised by their increase in signal, but it has meant that there has been no signal available to explore different conspicuity options with surrounding tissues, or to characterise normal cortical bone by measuring its relaxation times and studying the effect of contrast agent administration.

A potential method for detecting signal from cortical bone is the use of ultrashort echo time (UTE) pulse sequences where TE is reduced from the usual values for conventional T₁-weighted clinical sequences of about 4–10 ms to 0.07–0.20 ms [1], [2], [3], [4], [5]. Using this approach it is possible to detect signal from cortical bone before it has decayed to zero. We report our initial experience using this technique in normal volunteers and patients.

Section snippets

Subjects and methods

Studies were approved by the institutional review board. Seven adult volunteers [aged 29–85 years, four males (M) and three females (F)], two children with congenital muscular dystrophy [aged 7 years (F) and 10 years (M)], two patients with fractured tibias and fibulas [aged 56 years (F) and 18 years (M)], one with malunion of a tibial fracture 4 years after injury [aged 31 years (F)], one with osteoporosis following childhood polio [aged 32 years (F)], one with idiopathic osteoporosis [aged 55

Results

Using fat saturation and a surface coil, moderate signal was seen from the cortical bone in the tibia (Fig. 1A). The signal from cortical bone was much lower on the second echo (TE=5.95 ms) but was rendered more obvious by the subtraction of the second echo from the first (Fig. 1C).

Fig. 2A is a ds STUTE image (TR=650, TE=0.08, TI=80 ms image with the later echo [TE=5.95 ms] image subtracted from it). Cortical bone has a positive signal and is surrounded by a rebound (or cancellation) line from

Discussion

Signal was detected from cortical bone in all cases. In general, signal was apparent with the first echo (UTE) image but very low or zero on subsequent echoes. Intravenous contrast enhancement produced an increase in signal on the first echo and difference images.

Difference images were useful. Even though cortical bone had only a moderate signal on the first echo with many sequences, it had the shortest T₂ of the tissues examined and generally showed the largest difference in signal between the

Conclusion

Signal from cortical bone is now detectable in clinical MR studies and may show changes in disease of diagnostic value. These may prove to be complementary to the detailed studies already performed on trabecular bone [23] and provide a clinical application for findings already demonstrated in studies of in vitro bone samples [24], [25], [26] and with UTE phosphorus imaging [27].

Acknowledgments

We wish to thank Dulcie Rodrigues for preparation of this manuscript as well as the Arthritis Research Council for their support.

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Original contributionsMagnetic resonance imaging of cortical bone with ultrashort TE pulse sequences

Abstract

Purpose

Subjects and Methods

Results

Conclusion

Introduction

Section snippets

Subjects and methods

Results

Discussion

Conclusion

Acknowledgments

Clin Radiol

Magn Reson Imaging

Arch Oral Biol

Microvasc Res

J Biomed Eng

Magn Reson Imaging

J Magn Reson

Lung parenchyma: projection reconstruction imaging

Radiology

MR spectroscopic imaging of collagen tendons and knee menisci

Magn Reson Med

Magnetic resonance: an introduction to ultrashort echo-time imaging

J Comput Assist Tomogr

NMR studies of exchangeable hydrogen in bone

Proc Int Soc Magn Reson Med

Magnetization transfer in MRI: a review

NMR Biomed

Original contributions
Magnetic resonance imaging of cortical bone with ultrashort TE pulse sequences