MR Imaging Techniques

for the Assessment

of Osteoporosis

Renato Toffanin

Advanced Research Centre for Health, Environment and Space

ICICIP 2012, Mahendrapuri, Tamil Nadu, India

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Osteoporosis is a metabolic disease

characterised by low bone mass

and structural deterioration with

an increased fracture risk.

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and structural deterioration with

an increased fracture risk.

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Atraumatic

osteoporotic fractures

mainly affect the

proximal femur, the

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proximal femur, the

spine and the distal

radius.

Osteoporosis represents a major

public problem, with a high impact

on quality of life and high rates of

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on quality of life and high rates of

morbidity.

The osteoporosis landscape

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A big health worry for India

Over 30 million Indians have

osteoporosis and 80% are women.

The number of cases has almost

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The number of cases has almost

doubled in the last 10-15 years.

Clinical diagnosis

The established modality to

diagnose and monitor

osteoporosis is dual-energy X-ray

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osteoporosis is dual-energy X-ray

absorptiometry (DXA), which

provides areal bone mineral

density (BMD).

BMD measurement sites

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WHO guidelines

Osteopenia

NormalPeak Bone Mass

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Osteoporosis

T-Score

Osteopenia

-2.5 -2 -1 0

Fracture risk

BMD is a limited predictor of

fracture. It explains about 70% to

75% of the variance in strength.

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75% of the variance in strength.

Additional factors such as bone

architecture, tissue composition

and micro damage determine

bone strength.

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bone strength.

Accordingly, high resolution

imaging techniques are needed

for measuring bone quality.

Magnetic resonance imaging

(MRI) is an emerging technology

for acquiring high-resolution

images of cortical and trabecular

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images of cortical and trabecular

bone in vivo.

In conventional MRI, bone yields a

low signal and appears dark due

to the relatively low abundance of

protons and an extremely short T2

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protons and an extremely short T2

relaxation time (< 1 ms).

The MR signal stems largely from

the marrow, and depends on the

pulse sequence used and the fat

content of the marrow (fatty vs

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content of the marrow (fatty vs

hematopoietic bone marrow).

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Sagittal T1-weighted fast spin-echo image of the

calcaneus with an in-plane resolution of 195 µm.

Quantitative MRI

Information regarding structure,

topology and orientation of the

trabecular bone network can be

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trabecular bone network can be

extracted from the images by

applying digital processing

techniques.

Image analysis

Analysis of trabecular bone images

involves several post-processing steps:

outlining of the ROI, correction of the

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outlining of the ROI, correction of the

coil sensitivity, bone/marrow

segmentation, structural calculations

and, if needed, serial image

registration.

Trabecular bone analysis

Structural parameters are commonly

divided into 3 classes including scale

(e.g. volume of bone and thickness),

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(e.g. volume of bone and thickness),

topology (e.g. plate- or rode-like

structure) and orientation (e.g. degree

of anisotropy).

High-resolution MR image of the calcaneus acquired

at 3 T and a selected ROI. The color-coded map

illustrates the different assignments of bone voxel to

their closest junction based on minimum geodesic

distance (Source: Carballido-Gamio et al. Magn

Reson Med, 2009, 61: 448)

T2* measurements

Alongside high-resolution MRI for

structural analysis, T2* measurements

can be performed to assess bone

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can be performed to assess bone

quality.

T2* is sensitive to inhomogeneities

caused by susceptibility differences at

the interface between bone marrow

and trabecular bone.

T2* depends on trabecular bone

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T2* depends on trabecular bone

density and is shorter in normal

trabecular bone than in osteoporotic

tissue.

T2* mapping of the calcaneus

The preferred site for T2* relaxometry

is the heel bone, mostly composed of

spongy bone (95%). T2* mapping of

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spongy bone (95%). T2* mapping of

the calcaneus is extremely sensitive in

identifying changes in bone quality

that are not revealed by BMD.

CC

ST

TC

T2* map showing the examined calcaneal sites: cavum

calcanei (CC), tuber calcanei (TC) and subtalar region

(ST).

CC TC

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T2* mapping of the spine

Trabecular bone is also prominent in

the vertebral body (up to 90%). The

spine certainly represents the most

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spine certainly represents the most

critical site for quantitative MRI since

vertebral fractures are the most

common type of osteoporotic

fractures.

T2*WMRI: sagittal plane

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Monoexponential Levenberg-Marquardt fit algorithm

Image analysis: sagittal plane

Monoexponential Levenberg-Marquardt fit algorithm

Dahnke and Schaeffter, Magnetic Resonance in Medicine, 20052

L2 T2*W

MRI: axial plane

5 SLICES

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Image analysis: axial plane

Contacts

E-mail: toffanin@arches-centroricerca.org

E-mail: retoffanin@gmail.com

Skype: arches02

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Skype: arches02

www.arches-centroricerca.org