Multispectral optoacoustic tomography

To the Editor: In chronic inflammatory diseases, uncontrolled inflammation is associated with increased rates of hospitalization, complications, and death. Because of the potential severity of these conditions, there is an increased demand for new diagnostic approaches.1,2 Multispectral optoacoustic tomography (MSOT) is a new imaging technique that permits the noninvasive quantification of hemoglobin-dependent tissue perfusion and oxygenation as surrogates of inflammation.3 This approach uses the excitation of short-pulsed laser light with near-infrared wavelengths to induce the photoacoustic effect in targeted tissues, which results in detectable sound waves induced by thermoelastic expansion. In this single-center, cross-sectional diagnostic study (ClinicalTrials.gov number, NCT02622139), MSOT Acuity Echo (iThera Medical) was used to perform transabdominal evaluation of intestinal inflammation in 108 patients with Crohn’s disFigure 1 (facing page). MSOT Imaging for the Assessment of Crohn’s Disease Activity. Panel A shows the transabdominal imaging approach, which uses the same detector for laser light emission and ultrasonic detection of signal levels by means of multispectral optoacoustic tomography (MSOT). Erythrocytes are the target for laser-light absorption and ultrasonic emission. Six different wavelengths (700, 730, 760, 800, 850, and 900 nm) were used for MSOT data acquisition; MSOT measurements, such as total hemoglobin (Hb), oxygenated Hb, deoxygenated Hb, and oxygen saturation, are calculated from these measurements. These hemoglobin-based measurements permit the evaluation of tissue perfusion and oxygenation as surrogates of inflammation with MSOT. Panel B shows MSOT-derived total Hb signal levels in the intestinal wall (in both the large bowel and the small intestine) in 44 patients with Crohn’s disease with different degrees of endoscopic inflammation. Such evaluation was performed by means of the Simplified Endoscopic Score for Crohn’s Disease (SES-CD), which ranges from 0 to 56, with higher scores indicating a greater severity of intestinal inflammation; remission is defined as a score of less than 3, low disease activity as a score of 3 to 6, moderate disease activity as a score of 7 to 15, and high disease activity as a score of 16 or more. The signal levels are expressed as normalized z scores and transformed into a linear scale of arbitrary units (au). The red dots represent single measurements for each patient; the horizontal lines indicate medians, and I bars the interquartile range. A single asterisk denotes P<0.05 and a double asterisk P<0.001 for the comparison with remission. Panel C shows representative images of MSOT measurements of total Hb in the large bowel and small intestine in patients with different grades of endoscopic disease activity (as evaluated by means of SES-CD). The top row shows representative MSOT measurements of total Hb as color-coded maps with an overlay of B-mode ultrasonographic images. The middle row shows schematic representations of the images shown in the top row. The bottom row shows the corresponding endoscopic evaluation. this week’s letters