Diagnostic ultrasound imaging
A probe of piezoelectric elements sends short acoustic pulses into tissue and listens for echoes; the system beamforms them into real-time images and Doppler flow data.
Principle
The transducer contains an array of piezoelectric elements (or, in some designs, single crystal or capacitive micromachined elements) that convert electrical pulses into ultrasound, typically in the low-megahertz range for deep imaging and higher frequencies for superficial work, and convert returning echoes back into voltages. Because the system assumes a fixed average speed of sound in tissue (about 1540 m/s), the time of arrival of each echo gives its depth. A beamformer applies precise delays to the elements on transmit and receive to steer and focus the beam; after amplification, time-gain compensation, digitisation and envelope detection, each scan line becomes a column of brightness values (B-mode). Doppler modes measure the frequency or phase shift of echoes from moving blood to display velocity (colour, pulsed and continuous-wave Doppler). Most of the electronics is low voltage, but transmit pulses reach high voltage inside the system and probe. For the field engineer, the probe is by far the most frequent point of failure.
The chain, block by block
| Block | What it does | How it fails |
|---|---|---|
| Probe (transducer) | Piezoelectric array with matching layers, acoustic lens and backing, connected by a multi-coax cable to a connector with many pins. | Most common failure: dead elements give vertical dropout lines or shadow stripes; delaminated or cracked lens causes artefacts and an electrical safety risk; damaged cables, bent connector pins, worn strain reliefs. |
| Probe connector and probe select relays | Connect the chosen probe to the system's channels; on many systems relays or multiplexers switch elements to channels. | Probe not recognised, intermittent image when the cable is moved, single-channel faults on all probes connected to that port. |
| Transmit (pulser) and HV supply | Generates high-voltage drive pulses with controlled timing and amplitude for each channel. | No image on all probes, weak penetration, specific modes (e.g. CW Doppler) failing, HV supply errors. |
| Receive front end and beamformer | Low-noise amplifiers, time-gain compensation, ADCs and digital beamforming (delay and sum or software beamforming). | Channel-related artefacts on every probe, noise bands, loss of sensitivity; failures in a front-end board affect a set of channels. |
| Signal and image processing | B-mode detection, Doppler processing, scan conversion, image enhancement, measurements. | Mode-specific failures (e.g. colour Doppler noise or missing), software crashes after updates, wrong presets. |
| System power supply and cooling | Converts mains into the internal rails, often with a battery for transport or standby on portable systems; fans and filters cool the electronics. | Random shutdowns, failure to boot, overheating from clogged filters, battery degradation on portable units. |
| Display, user interface and peripherals | Monitor, touch panel, control panel, trackball, printers and recorders. | Stuck keys, trackball wear and dirt, touch panel failures, monitor backlight or cable faults. |
| Storage, network and DICOM | Local hard drive or SSD, DICOM transfer to PACS, worklist, structured reports. | Full disk, DICOM configuration lost after updates, network faults. |
Symptom → where to look first
| Symptom | Suspect first |
|---|---|
| Vertical dark lines or dropout in one sector of the image, one probe only | Probe dead elements or cable conductors; confirm on another port and with a probe tester. |
| Same dropout pattern on all probes | System side: probe select relays or receive front-end channels, not the probes. |
| Probe not recognised | Connector pins, probe ID circuit, port; try other port and another probe. |
| Image flickers or changes when cable is moved | Probe cable or strain relief damage near the handle or connector. |
| Poor penetration on all probes | Transmit power supply or pulser, or acoustic output settings; check with phantom. |
| Colour Doppler noise or flash artefacts only | Doppler processing, filters and presets first, then external electrical interference. |
| Random shutdown or fails to boot | Power supply, battery, overheating from blocked fans/filters, then storage drive. |
| Trackball or keys unresponsive | Dirt and wear on control panel components; clean before replacing. |
Safety
Site and infrastructure
- Grounded mains outlet with correct voltage; in areas with unstable supply, power conditioning or UPS recommended by the manufacturer.
- Room temperature and humidity within manufacturer limits; adequate airflow around the system vents.
- Network connection for PACS and worklist where used.
- Safe, tidy routing of probe cables and probe holders to prevent cable crushing and drops.
- Approved disinfectants and probe reprocessing area (including high-level disinfection for endocavity and TEE probes).
Preventive maintenance basics
- Inspect every probe: lens for cracks, swelling or delamination, housing, cable and strain relief, connector pins.
- Check each probe for dead elements using an image of air or a phantom, or a dedicated probe tester; keep a record per serial number.
- Perform electrical safety tests per IEC 62353 (or the locally required standard), including patient-leakage on applied parts; TEE probes need extra attention.
- Clean air filters and check fans; review temperature and error logs.
- Check image quality with a tissue-mimicking phantom: penetration, resolution, uniformity, compared with baseline.
- Check trackball, controls, touch screen, display, and printers.
- Verify disk space, backup of presets, DICOM and network configuration.
Safety
- Damaged probe lens or housing can expose the patient to electrical leakage; take such probes out of service and tag them.
- Internal transmit circuits carry high voltage; disconnect mains and allow discharge before opening the system.
- Treat all probes as potentially contaminated; clean and disinfect according to the reprocessing instructions before handling, especially endocavity and TEE probes.
- Observe ESD precautions when handling boards and probe connectors.
- Battery-powered portable systems: handle lithium batteries per manufacturer guidance; swollen batteries are a fire risk.
Manufacturers
GE HealthCare · Philips · Siemens Healthineers · Canon Medical Systems · Samsung Medison · Mindray · Fujifilm (incl. Sonosite) · Esaote · SonoScape · Hitachi/Fujifilm (former Aloka) · Chison