Ultrasound microscopy through a fine fiber for renal tissues

Abstract

To the Editor: Renal pathological assessment involves renal tissue examination using light microscopy (LM); however, there is an unavoidable bleeding risk. In addition, diagnosis is complicated when resected renal tissues contain a few glomeruli. Ultrasound (US) microscopy enables histopathological observations in real time using high-frequency US (≧ 100 MHz) [1, 2]. However, it has not been used clinically. We have been developing the US microscopy through a fine quartz fiber (1 mm in diameter) [3–5] to observe renal tissues in vivo; thereby, we could potentially perform safe and precise renal biopsy. For this purpose, we examined that this technology could obtain equivalent images of renal tissues with LM ex vivo. We prepared slide specimens of renal tissues from patients with glomerulonephritis using unstained US microscopic slides and periodic acid-schiff stained slides derived from paraffin-embedded tissue. Figure 1a shows the US microscopy imaging system through the fine fiber. This system consisted of a pulser/receiver (5900PR, Panametrics, USA), a transducer with frequency bandwidth 95–278 MHz (V2113, Panametrics), an imaging unit (JD5520DT-ATX, SonixTM, Inc, USA), a fine-tapered quartz fiber with a concave tip (length 33.2 mm, diameter of the large surface side 0.95 mm, diameter of the small surface side 0.81 mm), and an oscilloscope (Tektronix TDS 5104B, Test Equipment Connection, USA). We measured the focusing point of an ultrasonic beam radiated from the end of the fiber and obtained images of the slide specimens placed in water. An ultrasonic pulse (approximately 50 Vp-p amplitude) with frequency bandwidth of 95–278 MHz was transmitted into the fiber. In contrast to a B-mode image obtained with the conventional ultrasonic diagnostic equipment, a planar image perpendicular to an ultrasonic beam is obtained in the US microscopy. The planar image of the US microscopy is called “C-mode image,” and is a similar image to LM. In C-mode imaging, the minimum scanning interval of the ultrasonic beam was 10 μm, and the minimum scanning widths in the Xand Y-directions were each 1 mm. Figure 1b, c shows the images obtained by the US microscopy (US frequency: 125 MHz) and LM. We could identify mesangial cell proliferation, increased matrix, and fibro-cellular crescent as well as discriminate between glomeruli and renal tubules using the US microscopy. This was sufficient information to diagnose the patient. We succeeded in obtaining renal tissue images using US microscopy through a fine quartz fiber ex vivo. Furthermore, these images were similar to those of LM. This preliminary study provides a first step toward clinical application of US pathological observation in renal diseases. In addition, we could obtain equivalent images up to depth of approximately 5 mm by adjusting the ultrasonic beam radiation. Renal biopsy is usually performed as a percutaneous closed procedure under the US guidance. The risk of the procedure includes bleeding. Meanwhile, the fine fiber US microscopy enables real-time imaging of renal tissues and avoids obtaining few glomeruli containing. This enables a safe and precise renal biopsy, and we can thereby make precise diagnoses of renal diseases. This study provides an important contribution to future diagnoses, and further development is expected.