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Author: Meertens, Robert

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The use of near infrared spectroscopy (NIRS) as a diagnostic tool to measure microvascular haemodynamics in bone tissue.
Robert Meertens, Karen M Knapp, William D Strain, Francesco Casanova
University of Exeter Institute of Health Research
Project Background:

Results:

Bone is a dynamic and highly vascular tissue, but measuring markers
of microvascular haemodynamics within bone is currently difficult.
There are logistical and technical limitations with existing tests
based around MRI and radioisotope scans, in part due to bone’s high
density and mineral content. This complicates studying bone
diseases where microvascular dysfunction plays a pathogenic role.

 Total oxygenation index (TOI): The ratio of O2Hb to total
haemoglobin (cHb);

80

90

100

Figure 1: The Hamamatsu NIRO
NX-200 (a) demonstrates the
NIR emitting sensor probe (left)
and the detector probe (right);
(b) shows the typical real time
display data including TOI, nTHI,
O2Hb, HHb and cHb changes.

Primary Aim and Objectives:
To investigate the potential of NIRS as a diagnostic tool in
the measurement of microvascular haemodynamics in
bone tissue, including whether NIRS:

70

TP
PATELLA

TD
TP
MM
PATELLA
MUSCLE
80.55 (4.60) 83.00 (4.13) 81.18 (6.14) 82.20 (8.37) 70.05 (4.82)
5.71

4.98

7.56

10.18

6.88

p<0.001

p<0.001

p<0.01

p<0.01

n/a

Figure 5: Box plot of mean baseline TOI values (n=15)

32 arterial occlusions were attempted on 15 participants
(alternating between TD and TP) of which 27 sets of
successfully paired bone and muscle data (12 TP and 15 TD)
were recorded. There was a significant statistical difference
demonstrated between bone sites and the simultaneous
muscle tissue data taken for a number of different parameters
including:
- Baseline pre occlusion TOI means;
- Post occlusion gradients of TOI and HHb desaturation;
- Occlusion release gradients of TOI and HHb measured during
the first 20 seconds post cuff release; and,
- Hyperaemic response upon occlusion release.
Variability is higher with occlusion data but is again
comparable between bone and muscle readings. Further
investigations showed no obvious systematic confounding in
results caused by age, gender or leg circumference.

TP Bone
81.65
-1.62
23.28
16.24
-146.26
0.69

DATA FROM TP ARTERIAL OCCLUSIONS

TOI Baseline (%)
TOI desat (%/min)
HHb desat rate (µM.cm/min)
TOI resat (%/min)
HHb resat rate (µM.cm/min)
Hyperaemic Response (% TOI)

SD
4.14
0.54
7.25
11.86
91.59
1.44

Muscle
SD
p-value
70.96
5.00 0.0029
-3.64
1.77 0.0121
52.79
23.87 0.0047
75.19
31.40 0.0022
-812.00 370.12 0.0022
5.80
3.20 0.0022

TD Bone
SD
Muscle
SD
p-value
TOI Baseline (%)
80.08
5.05
70.83
4.58
0.0008
TOI desat (%/min)
-1.86
0.55
-3.94
1.96
0.0045
HHb desat rate (µM.cm/min)
28.02
6.27
54.32
24.70 0.0045
TOI resat (%/min)
16.85
7.51
67.89
27.03 0.0008
HHb resat rate (µM.cm/min)
-153.61 56.53 -711.95 301.96 0.0007
Hyperaemic Response (% TOI)
1.17
1.34
5.93
2.53
0.0007
Figure 8: Descriptive results of TD, TP and muscle physiological data. Wilcoxon
signed–rank tests demonstrate statistically significant differences between bone
and muscle.
DATA FROM TD ARTERIAL OCCLUSIONS

Figure 7: Graphs show an individual example of observed differences in bone (blue) and muscle (orange) physiology.
Occlusion point

300

85

Hyperaemic response

70

Baseline TOI

60

TOI resaturation rate

55

50

TOI desaturation rate

Time (s)

O2Hb and HHb

100

100

50

0

100

0

-100

-100

-300

Time (s)

Time (s)

Conclusions:
Despite the statistical significance of the measured differences between bone and muscle, the physiological importance of these
differences remains essentially unknown due to a paucity of research in this field. However, the results of this feasibility work are
encouraging and justify further research into the use of NIRS as a diagnostic tool for bone pathologies including microvascular
pathogenesis, such as osteoporosis, non-union, osteoarthritis, Pagets, and/or blood bourne cancers. If successful, further studies
investigating the use of NIRS in more diverse populations would be justified. This could lead to inexpensive, quick and tolerable
methods of measuring microvascular supply in bone.

50

0
2322
2334
2346
2358
2370
2382
2394
2406
2418
2430
2442
2454
2466
2478
2490
2502
2514
2526
2538
2550
2562
2574
2586
2598
2610
2622
2634
2646
2658
2670
2682
2694
2706
2718
2730
2742
2754
2766
2778
2790
2802
2814
2826
2838
2850
2862
2874
2886
2898
2910
2922
2934

Concentration (µM.cm)

150

150

HHb resaturation rate

200

-200

40

200

200

HHb desaturation rate

-50

45

Figure 3: Arterial Occlusion set up: A BP cuff is
around the distal femur. NIRS probes are
secured with bandages.

Concentration (µM.cm)

TOI (%)

75

Methods:

300

250

80

65

O2Hb

2322
2334
2346
2358
2370
2382
2394
2406
2418
2430
2442
2454
2466
2478
2490
2502
2514
2526
2538
2550
2562
2574
2586
2598
2610
2622
2634
2646
2658
2670
2682
2694
2706
2718
2730
2742
2754
2766
2778
2790
2802
2814
2826
2838
2850
2862
2874
2886
2898
2910
2922
2934

90

HHb

TOI
Occlusion release

Concentration (µM.cm)

Figure 2: Schematic probe positioning at four
bony sites and one muscle site.

2) Can provide reproducible measurements across
different anatomical sites, participants and operators.

Arterial occlusion integrity was confirmed by a decrease
in TOI and simultaneous matched changes in HHb and
O2Hb during and after occlusion, with a nTHI change of
less than +/- 15% during occlusion suggesting blood
volume remained constant (Figure 4).

Mean TOI (%)
Coefficient of
Variation (%)
Wilcoxon
signed-rank
test vs muscle

60

TD
MM
MUSCLE

 Real time absolute concentration changes of HHb,
O2Hb and cHb [1].

Femoral artery occlusions were undertaken whilst
simultaneously taking NIRS measurements at a bony site
(TD or TP) and the muscle site before, during and after
occluding blood flow at the distal thigh (Figure 3 shows
set up).

Figure 6: Summary of baseline TOI results (standard deviation is in parenthesis; n=15)

Anatomical Sites

 Normalised total haemoglobin index (nTHI): Real time
percentage change in cHb concentration from an initial
baseline measurement; and,

Testing was carried out on healthy volunteers, recruited
using convenience sampling, with institutional ethical
approval. Participants were positioned supine with
baseline TOI measurements taken at four different
superficial bony anatomical locations (proximal tibia (TP),
tibial diaphysis (TD), medial malleolus (MM) and patella)
and one muscle location, as shown in Figure 2.

Baseline TOI measurements on 15 participants demonstrated statistically
significant differences between baseline TOI at the four bone sites and the muscle
site. The variability of results at the preferred TD and TP bone sites was
comparable to muscle readings (an established site for NIRS measurements).

Baseline TOI for Anatomical Sites of the Leg
Total Oxygenation Index (%)

Near infrared spectroscopy (NIRS) has the potential to measure
bone haemodynamic markers in real time and is safe and
inexpensive. It also provides information on oxygen levels within
bone, previously only possible with bone biopsy. NIRS utilises similar
technology to a pulse oximeter, transmitting and receiving
designated optical frequencies using non-invasive probes at a
specific anatomical sight and measuring tissue depths of up to 4cms
(Figure 1). NIRS takes advantage of the differences in attenuation
caused by oxyhaemoglobin (O2Hb) and deoxyhaemoglobin (HHb).
This provides haemodynamic markers such as:

1) Can exclusively measure bone tissue, based on the
known physiological differences between bone and
muscle.

Author Contact:
E-mail: R.M.Meertens@exeter.ac.uk
Phone: 01392 722511
@RobertMeertens

-50

References:

-100

-150

-200

Occlusion
Starts

Time (s)
HHb TP

Occlusion
Released

O2Hb TP

Figure 4: O2Hb and HHb experience equal
and opposite changes during occlusion and at
occlusion release.

Binzoni, T. and L. Spinelli (2015). "Near-infrared photons: a non-invasive probe for studying bone blood flow regulation in humans."
Journal of physiological anthropology 34(1): 1-6.

Acknowledgements:
The authors would like to thank the College of Radiographers Industry Partnership Scheme (CoRIPS) for their support of this ongoing
PhD project via the CoRIPS Doctoral Fellowship Grant. Thanks also goes to all participants, Clare Thorn and all the staff at the
Diabetes and Vascular Research Centre, Exeter.

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version of
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