Garcia_edit_new.qxp 25/7/08 03:17 Page 108
Interventional Cardiology
Other Imaging Techniques Raman spectroscopy technology collects scattered light with optical fibres
and routes the collected signal to spectrometer systems for analysis.
Thermography Previously, fibre optic probes utilised a region of the Raman spectrum
Atherosclerosis is accompanied by inflammation, and vulnerable plaques called the ‘fingerprint’ (FP) region (<~1,800cm
-1
shifted light) to conduct
have been associated with increased macrophage activity, metabolism remote assays, but due to technical problems with this approach it has
and inflammation.
23
In a prospective study, an association between recently been replaced by using another region of the Raman spectrum,
temperature heterogeneity and the incidence of adverse events at follow- called high-wavenumber (HW) Raman shifted light (>~2,500 cm
-1
shifted
up was found in patients with coronary artery disease undergoing a light). This allows us to collect Raman spectra via a single optical fibre,
successful percutaneous intervention.
24
In addition, treatment with simplifying the size and complexity of the catheter and making this
statins seems to affect the thermographic results: in non-CLs the method clinically feasible.
34
Thus, the optical catheter system (OCS)
temperature difference (DeltaT) was lower in the group treated with (vPredict™) has been introduced as a tool for measuring the chemical
statins compared with the untreated group (0.06±0.05 versus composition of coronary vessels in vivo using Raman spectroscopy and
0.11±0.10°C; p=0.05).
25
the subsequent mapping and quantification of the vessel and plaque
components for evaluating plaque progression. In a xenograft model,
More recently, a correlation between the morphological and functional lipid-laden plaques were identified with the collected Raman spectra by
characteristics of CLs in patients with ACS and chronic stable angina utilising the overall cholesterol content, i.e. the sum of the free
has been reported.
26
In 81 consecutive patients (48 with ACS and 33 cholesterol and cholesterol esters contents, and setting a decision
with stable angina), Ri by IVUS and DeltaT by thermography between threshold at 12%, as determined in previous studies. As expected, the
the CL and the proximal vessel wall were measured. Patients with ACS lipid-laden plaques exhibit an increased free cholesterol and cholesterol
had a higher Ri than patients with CSA (1.15±0.18 versus 0.90±0.12; ester content, while the non-atherosclerotic samples are mainly protein
p<0.01), as well as increased DeltaT (0.08±0.03 versus 0.04±0.02ºC; and triglycerides.
p<0.01). Patients with positive Ri had higher DeltaT than patients with
negative Ri (0.07±0.03 versus 0.04±0.02ºC; p<0.001). Patients with Alternatively, near-infrared (NIR) molecular vibrational transitions can be
rupture plaque had increased DeltaT compared with patients without measured in the NIR region (750–2,500nm),
35
and laser spectroscopy
rupture plaque (0.09±0.03 versus 0.05±0.02ºC; p<0.01). Multivariate using wavelengths of 360–510nm has been evaluated in vitro.
36
NIR
analysis showed that DeltaT was independently correlated with the spectroscopy observes how different substances absorb and scatter NIR
presence of rupture plaque, positive Ri and ACS. However, there are light to different degrees at various wavelengths. An NIR spectrometer
several factors that deserve further investigation. The impact of emits light into a sample and measures the proportion of light that is
different coronary flow conditions on plaque temperature (‘cooling returned over a wide range of optical wavelengths. The return signal is
effect’) is still not completely understood.
27
Simulations have revealed then plotted as a graph of absorbance (y axis) at different wavelengths
that the correct interpretation of intravascular thermographic (x axis), called a spectrum. In aortic and coronary artery autopsy
measurements requires data on the flow and the morphological specimens, the ability of the technique to identify lipid-rich TCFA
characteristics of the atherosclerotic plaque. through blood has been confirmed.
37
Initial clinical experience in six
patients with stable angina demonstrates that high-quality NIR spectra
There are a few limitations to the routine use of thermography in the can be safely obtained.
28
Additional studies are planned to validate the
catheterisation laboratory: ability of the technique to identify lipid-rich coronary artery plaques
and ultimately link chemical characterisation with subsequent
• most of the catheters used still comprise over-the-wire systems; occurrence of an ACS.
38,39
• accurate temperature assessment requires direct contact of the
thermistors with the vessel wall, with the associated potential risk of Treatment
endothelial damage; and Treatment of asymptomatic, non-obstructive coronary lesions may be a
• because the temperature within the vessel changes rapidly with fluid desirable pursuit, but a pre-emptive strike may be a risky, time-
application, any intracoronary injection of contrast dye, flush or consuming and expensive proposition. Assumptions include:
medication has to be avoided before and during measurements.
• accepting that the specific pathology can be defined in living subjects;
Raman and Near-infrared Spectroscopy • presuming that this particular pathology is responsible for future
A number of spectroscopic intravascular imaging techniques have been clinical events; and
developed recently and are still under investigation.
28
Spectroscopy can • presuming that the ‘fingerprint’ of this pathology can be
provide qualitative and quantitative information about chemical plaque reliably detected.
composition. The Raman effect is created when incident laser light
(typically 750–850nm wavelength) excites molecules in a tissue sample, Based on these assumptions, initial risk stratification of asymptomatic
which then scatter light at a different wavelength. This change in patients drawn from the general population will be required, likely
wavelength, known as the Raman effect, is dependent on the chemical using an early screening method able to detect ‘non-obstructive high-
components of the tissue sample
29,30
and can therefore provide risk lesions’.
quantitative information about molecular composition.
31–33
Raman
spectroscopy has shown acceptable correlation compared with Focal Therapy
histology (r=0.68 for cholesterol and r=0.71 for calcification)
33
and Myocardial infarctions are typically the result of focal complex or
with IVUS in vitro.
32
vulnerable lesions, and it is quite reasonable that many interventionalists
108 EUROPEAN CARDIOLOGY
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