How High-Frequency Coaxial Cable Supports Cleaner Signals in Advanced Imaging Probes

Transmitting these highly complex signals—including those used in IVUS ultrasound imaging, ICE intracardiac imaging, and high-definition (HD) endoscopy systems — requires highly sensitive analog signal transmission from the probe transducer to the imaging processor. Most of these signals operate above 5 MHz, with some exceeding 50 MHz, enabling the high-resolution imaging required to identify potential abnormalities and support accurate diagnosis and intervention. However, high-frequency signal transmission is susceptible to attenuation, impedance mismatch, phase distortion, and electromagnetic interference, all of which can reduce image clarity. At Hotten, we manufacture high-frequency coaxial cable assemblies for advanced imaging probes. The following four core technologies enable reliable signal transmission and support high-quality diagnostic imaging.

Ultra-Low-Loss Dielectrics for Minimal Attenuation Across Frequency Bands

Signal attenuation of coaxial cable depends on the frequency due to the skin effect and loss of signal in the dielectric of the cable. Low-level return signals from deep tissue can experience more than 1.5 dB/m of signal loss when transmitted through conventional cables at 20 MHz. Advanced low-loss dielectric materials, such as expanded PTFE (e-PTFE) and microporous polyethylene with a dissipation factor below 0.0005 at 10 MHz, are used by Hotten. These materials help maintain weak reflected signals above the noise floor in IVUS and ultrasound probe cables while achieving an insertion loss below 0.3 dB/m at 30 MHz. The permittivity is very stable even in the e-PTFE's porous microstructure, thus avoiding attenuation drift during the course of a long scanning session. This directly contributes to improved image resolution and enhanced tissue penetration.

Precision Impedance Matching to Eliminate Signal Reflections

Discontinuities in characteristic impedance at cable splices, connector interfaces, or due to manufacturing variations can introduce image artifacts, including ghosting and range sidelobes. Every component is verified using Hotten’s patented closed-loop extrusion control and time-domain reflectometry (TDR) systems, which will achieve an impedance tolerance of less than 2% (when used in medical imaging, it is considered 50 ohm nominal cable). Our attention is also focused on the interface of the cable to the internal flex circuit of the probe for our ICE catheter cables and endoscope imaging harnesses—as we custom design the transition boards to match the impedance of the cable, instead of a sharp transition. The continuity in impedance eliminates ring down artifacts that could be confused with disease. All measurements show a VSWR of < 1.2:1 for the entire band.

Phase-Stable Construction for Consistent Delay Characteristics

The relative phase alignment of multiple signal paths within phased-array or multi-element imaging probes is critical for accurate beamforming. With a varying geometry and/or material of the cable between channels, the reconstructed image will be misregistered and/or blurred because of the differences in the timing of arrival of the signal. Hotten achieves phase stability through three key approaches: (1) High dielectric constant uniformity within each production batch; (2) High-precision signal path length matching of signal path (e.g. tolerances within ±1 mm) for multi-coaxial bundles; (3) A dense braid shield provides uniform capacitance, even when flexed. We also do thermal equalization on our robotics wire harnesses for automated imaging systems in order to remove internal stresses that may lead to phase drift. This provides coherent beamforming, with phase errors of less than 2° at 10 MHz.

Comprehensive Shielding for Rejection of External and Internal Noise

In a few instances imaging probes are employed together with other radiative technologies including electrosurgical systems and the well-known device causing noise in poorly-shielded coaxial cables, the fluoroscopes. Other causes of noise could be generated internally as in, for example, the effects produced in cables due to movements being picked up. By using a three-layer shielding design, Hotten protects your device with a combination of a semiconductive layer inner (retaining triboelectric charges), a highly braided silver-plated copper shield (95% shielding effectiveness, reducing magnetic interference from external sources) and an outer shield foil (100% shielding of electrical field coupling). In order to reduce common mode currents, a stranded ground return conductor for the IVUS and ICE cable of intravascular catheters is provided. The overall result is transfer impedance of less than 3 mΩ/m at 30MHz providing for clean signals that will yield high contrast, artifact-free images.

Conclusion

Not only do the advanced imaging probes yield cleaner signals, they are the result of careful selection of the dielectric material, the impedance control applied and design of the phases and shields of the probes. High-frequency coaxial cable assemblies are utilized in ultrasound probes, ICE catheters, IVUS harnesses, and endoscope systems to preserve the integrity of acoustic and optical signals at the probe tip. We have developed more than 400 cable variants and operate over 40 cable production lines annually, with more than 10,000 meters of manufacturing capacity dedicated to supporting imaging systems that enable accurate clinical diagnoses and achieve excellent patient outcomes.