Medical Design Briefs - October 2024 - 17

sures the extent to which those x-rays
were absorbed by different tissues. Dense
materials like bone absorb more x-rays
than softer tissues.
Trends in Imaging
Fixed Mirror
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 crosssectional
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
Tunable Laser
Beam Splitter
Eye
Signal = Light
Fig. 3 - Optical coherence tomography diagram.
Balanced Photodetector
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.
Digital X-Ray Detector
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- todigital
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.
Power
Supply
X-Ray
Source
Sample
Signal = X-Ray Radiation
Low Noise Amplifer
ADC
Fig. 4. - X-ray diagram.
Medical Design Briefs, October 2024
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