Medical Imaging: Trends Shaping Diagnostic Advancements

The integration of advanced technologies is driving significant improvements in medical imaging and diagnostic capabilities. This article explores key modalities like ultrasound, MRI, OCT, x-ray, CT, and PET, as well as several emerging trends that are driving performance improvements (see Table 1).

Ultrasound

Noninvasive diagnostic ultrasound is used to imagine tissues inside the body. Ultrasound probes (i.e., transducers) produce sound waves, and when placed on the skin or inside the body, they transmit those waves into the body and detect returning echoes (see Figure 1). Based on the speed of sound and the timing of echo returns, the system calculates the distance between the transducer and the tissue. These distances are used to create two-dimensional images of the tissues of interest. Diagnostic ultrasound includes images of internal organs and functional maps to visualize changes happening inside the body.

Ultrasound systems include three main components: a transmitter, a transducer, and a receiver. The transmitter and receiver are electronic components while the transducer is mechanical. The transducer is responsible for generating and receiving ultrasound waves. With the help of piezoelectric quartz, like PZT and ceramics, transducers convert electrical energy into mechanical (i.e., sound) energy. Capacitive micromachined transducers (cMUTs) and piezoelectric micromachined transducers (pMUT) are growing in popularity as a cost-effective alternative.

The transmitter is responsible for amplifying signals from the transducer; inside the transmitter, power amplifier design plays a significant role in overall performance. Receivers amplify weak signals from the transducer for the sake of transmission. Inside the receiver, the low-noise amplifier (LNA) determines the signal-to-noise ratio (SNR), and by extension, performance.

Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) leverages a magnetic field and computer-generated radio-frequency pulses to generate detailed 2D or 3D images of organs and tissues inside the body. This technology operates on the principles of nuclear magnetic resonance (NMR) (see Figure 2).

An MRI machine generates a magnetic field that typically ranges in strength from 1.5 to 3 T. The field varies across the sample to form a gradient, and detection algorithms determine precisely where the signal is coming from. The machine emits RF pulses that disturb the gradient, and the coils in the MRI machine detect the rate at which it returns to its original state once the RF pulse is turned off (i.e., relaxation). That data is collected and processed to create detailed images based on relaxation times and signal intensities from different tissues.

MRI functionality relies on its magnet system, gradient coils, RF system, and control computer. The superconducting magnet generates the magnetic field and maintains superconductivity with the help of cryogenics. Gradient coils create the variable magnetic field that enables image creation; amplifiers power the coils and determine the strength and timing of gradients.

RF coils transmit RF pulses to disrupt the gradient and detect returning signals during relaxation. Meanwhile, an RF transmitter and receiver support their function by generating, detecting, and amplifying the RF signals for further analysis. A control computer is responsible for both managing these operations and storing image data.

Optical Computed Tomography

The principle behind optical computed tomography (OCT) is white light interferometry, also known as low-coherence interferometry. This measurement technique requires an interferometer (e.g., Michaelson Interferometer) to make precise distance measurements. OCT leverages these measurements to form precise maps of surface details. For example, OCT makes it possible for cardiologists to image the microstructures of coronary arteries at a higher resolution than other existing imaging modalities (e.g., intravascular ultrasound, x-ray angiography) (see Figure 3).

The system traditionally includes a low-coherence light source, interferometry, a scanning system, high-sensitivity detectors, and image reconstruction algorithms; however, there are a variety of scanning techniques available depending on speed and resolution requirements.

Mechanical scanning, more common in time-domain optical coherence tomography (TD-OCT), involves physically moving the mirrors in an interferometer setup to change the path length of the light. Mirror adjustments make it possible to measure optical path differences. The other approach to scanning involves altering the wavelength of the light source without mechanical movements. This method is made possible by highly sensitive tunable lasers, and it’s more common in Fourier-domain optical coherence tomography (FD-OCT).

X-Ray and Computed Tomography (CT)

Both x-ray and computed tomography (CT) rely on x-rays to create images of internal body structures by leveraging radiation. In x-ray imaging, x-rays pass through the body, and the system measures the extent to which those x-rays were absorbed by different tissues. Dense materials like bone absorb more x-rays than softer tissues.

The pattern of x-ray absorption is recorded as a 2D image of internal body structures in silhouette. CT imaging takes this a step further by rotating the x-ray source to capture 2D images at different angles. Once reconstructed, healthcare professionals have access to cross-sectional 3D images for a more comprehensive view of soft tissues, blood vessels, and organs, not just bones and other dense structures (see Figure 4).

An x-ray machine typically features an x-ray vacuum tube where the x-rays are generated. The tube includes a cathode and anode to facilitate the electron collisions that produce x-rays. A high-voltage power supply serves as a generator, supplying the voltage to accelerate the electrons. Modern systems have collimators for beam shaping and film or digital detectors to process the electronic signals used to produce digital images. CT imaging builds on this technology with a rotating x-ray source, multi-detector arrays, and more sophisticated image reconstruction software to facilitate the creation of cross-sectional images.

Positron Emission Tomography (PET)

Positron emission tomography (PET) relies on nuclear medicine techniques to better understand metabolic processes in the body. To start, a biologically active, radioactive tracer is injected into the patient’s body. The tracer typically accumulates in areas with high metabolic activity (e.g., cancer cells, areas of inflammation). The radioactive isotope in the tracer is subject to positron emission decay, where it emits a positively charged electron (i.e., a positron). When a positron encounters an electron in the body, annihilation occurs, converting their combined energy into gamma photons. The PET scanner, consisting of a ring of detectors surrounding the patient, is lined with crystals that convert the gamma photons into light that can be detected by solid-state detectors. The PET system uses this information to construct 3D images for diagnosing and monitoring different disease states. PET can also be used for quantitative analysis; tracking the concentration of the tracer indicates metabolic rates in tissues (see Figure 5).

PET relies on radioactive tracers, a PET scanner, which includes scintillation crystals and solid-state detectors, data acquisition and processing (i.e., ADCs, data processing units), and image reconstruction algorithms. Together, these technologies enable PET to provide a detailed picture of metabolic processes in the body.

Trends in Imaging

Medical professionals rely on these imaging techniques for diagnosing diseases and injuries, monitoring treatment performance, and surgical planning. Improving medical imaging technologies leads to advancements in patient outcomes and access to care. Each imaging modality is designed with different clinical use cases in mind, but these trends show up in different ways across modalities. Below are a few examples.

Higher Resolution Imaging. In imaging applications, higher performance means sharper image quality and more accurate information for healthcare professionals looking to make diagnostic and treatment decisions.

For example, while 3T is still common, researchers have access to MRI systems with field strength up to 7T now. Higher field strength enhances signal-to-noise ratio (SNR) for clearer, more detailed results. With higher resolution and higher frequency analog-to-digital converters (ADCs) available, MRI receivers are also becoming more digital, representing yet another opportunity to reduce noise and SNR when power consumption is well managed. On the patient side, performance improvements translate to reduced scan times and cost reduction.

Designing for Portability. Many different types of imaging equipment used for patient assessment and treatment started out in controlled environments to preserve functionality (e.g., MRI suite). While modalities like MRI and CT are effective for diagnosis, they can be physically demanding for critically ill patients. Technological development is moving these diagnostic services to where patients are rather than expecting them to come to a treatment center.

Design for portability means considering factors like size, weight, power, magnetic field strength, cost, image quality, and safety. Component selection becomes very important for maintaining stable and efficient power generation and signal processing in a smaller footprint.

Synergy of Technologies. It’s becoming more common to see hybrid imaging technologies designed for a more detailed view of the body. For example, PET/MRI scans integrate PET scans and MRI scans. MRI contributes detailed images of internal body structures and PET highlights functional abnormalities using tracers. This is particularly useful for cases of Alzheimer’s disease, epilepsy, and brain tumors. In the past, this kind of holistic analysis wasn’t possible because MRI magnets interfered with PET’s imaging detectors.

Ultrasound and OCT are another complementary pair. When combined, healthcare professionals can gather high-resolution images of both superficial and deep tissues and structures. Since ultrasound is useful for capturing functional images and dynamic processes and OCT provides structural imaging with fine details, combining them offers a detailed structural and functional assessment in a single scan. This is particularly useful in specialties like ophthalmology, cardiology, dermatology, and oncology.

Advancements in medical imaging technologies are changing the way healthcare professionals approach diagnoses and patients receive care. These imaging modalities offer increasingly detailed, accurate, and comprehensive insights into the human body. The ongoing trends toward higher resolution, greater portability, and hybrid imaging are part of a larger trend toward precision medicine and more personalized, efficient, and effective healthcare.

This article was written by Peter Matthews, Product Director, Knowles Precision Devices, Itasca, IL. For more information, visit here  .

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