Versatile flexible spatial temporal resolution Modified Rosette Novel PETALUTE

This article highlights a collaborative effort between Purdue University, the University of North Carolina at Chapel Hill’s Biomedical Research Imaging Center, and the University of Cambridge aimed at advancing the capabilities of preclinical MRI through the development and validation of novel acquisition strategies—most notably
the PETALUTE sequence—for high-res- olution, multicontrast imaging of both
1H and X-nuclei (eg, 23Na, 31P) signal components. These efforts are designed
to enhance sensitivity, minimize artifacts, and facilitate detailed visualization of short-transverse relaxation time
(T2*) species and metabolic processes
crucial to translational neuroscience
and disease modeling.

1. MRI Monitor By Uzay Emir, PhD, and Stephen Sawiak, PhD
In Sequence
Novel MRI Sequence Enhances
Preclinical Imaging
A
s global health care systems
face mounting challenges
from pervasive labor short-
ages and escalating costs,
the 2024 Deloitte Global Healthcare
Sector Outlook
1
highlights the increas-
ing demand for technological advance-
ments that enhance and expedite
analytical capabilities. In this context,
MRI is transforming its role beyond
traditional diagnostics, establishing
itself as a powerful tool for investigat-
ing molecular and cellular mecha-
nisms in living organisms.
Against this backdrop, a 2025 pro-
jection by Nature Medicine
2
estimates
that the number of individuals liv-
ing with dementia in the United States—
currently the seventh leading cause
of death and a major contributor to
global disability, according to the
World Health Organization
3
—will
nearly double over the next 35 years,
resulting in nearly 10 million new
cases annually. This growing bur-
den underscores the urgent need for
advanced imaging technologies that
can detect early microstructural and
biochemical brain changes before
clinical symptoms emerge.
Recent advances in MRI, especially
at high and ultrahigh field strengths,
have greatly expanded the ability to
noninvasively study neurotransmitter
dynamics, microstructure, and energy
metabolism in the brain. These devel-
opments are accelerating discoveries
across various pathologies—including
epilepsy, neurodegenerative diseases,
brain tumors, and conditions involv-
ing autonomic and neuroendocrine
dysfunction—by allowing functional,
structural, and metabolic imaging
within a single modality.
While MRI has traditionally played
specific roles in clinical diagnostics
and research, its integration into
preclinical imaging pipelines has
gained momentum as a valuable link
between molecular mechanisms and
translational results. Preclinical MRI
provides a platform for high-resolu-
tion validation of new techniques,
enabling the improvement of contrast
methods, acquisition strategies, and
reconstruction algorithms before they
are applied in humans. In this con-
text, methods such as PETALUTE not
only promote preclinical science but
also help reduce risks and accelerate
clinical translation by enabling quan-
titative, artifact-resistant imaging
at the molecular and cellular levels
(Figure 1).
This article highlights a collabora-
tive effort between Purdue University,
the University of North Carolina at Cha-
pel Hill’s Biomedical Research Imaging
Center, and the University of Cam-
bridge aimed at advancing the capa-
bilities of preclinical MRI through the
development and validation of novel
acquisition strategies—most notably
the PETALUTE sequence—for high-res-
olution, multicontrast imaging of both
1
H and X-nuclei (eg,
23
Na,
31
P) signal
components. These efforts are designed
to enhance sensitivity, minimize arti-
facts, and facilitate detailed visualiza-
tion of short-transverse relaxation time
(T2*) species and metabolic processes
crucial to translational neuroscience
and disease modeling.
Improving Image Capture
The researchers aimed to overcome
longstanding limitations in ultrashort
echo time (UTE) MRI for molecular
imaging. Their goal was to improve
signal-to-noise ratio (SNR), spatial
resolution, and acquisition speed for
both
1
H-based metabolic imaging and
X-nuclei modalities, including
23
Na,
31
P,
2
H, and
13
C.
Traditional molecular MRI and MR
spectroscopic imaging techniques
often involve compromises between
spatial resolution, scan time, and
sensitivity, especially when targeting
low-abundance metabolites, rapidly
decaying signals, or nonproton nuclei.
Single-voxel or localized spectroscopic
methods typically require lengthy
acquisition times and have limited
spatial coverage. In contrast, conven-
tional techniques may insufficiently
sample central or peripheral regions of
FIGURE 1
Abdominal imaging in mouse (A) and man (B) with the same dual-echo PETALUTE
protocol. Comparison of the first (top) and second echo (bottom) shows the novel
contrast opportunities of ultrashort imaging, particularly around the liver, kidney,
stomach, skeletal muscle, and the mouse. The trajectory is robust to motion,
facilitating self-navigated gated reconstruction, vital for translational studies and
noncooperative patients. The mouse image was acquired at 7 T (BioSpec 70/30,
Bruker Instruments, FA 4°). The human image was acquired using a clinical 3 T MRI
system (Siemens Prisma). Together, these illustrate PETALUTE’s translational potential
across species and field strengths.
9
IMAGE COURTESY OF PURDUE UNIVERSIT Y, INDIANAPOLIS, AND THE UNIVERSIT Y OF NORTH
CAROLINA AT CHAPEL HILL’S BIOMEDICAL RESEARCH IMAGING CENTER.
28RADIOLOGY TODAY • OCTOBER 2025

2. k-space, thereby reducing quantifica-
tion accuracy and anatomical detail.
The PETALUTE sequence, a novel
3D dual-echo UTE MRI sequence,
tackles these issues with a multi-
echo UTE design based on a modified
rosette k-space trajectory that stra-
tegically oversamples both the center
and edges of k-space. This approach
allows for efficient volumetric imag-
ing of short-T2* species across vari-
ous nuclei, offering improved SNR
and spatial accuracy. Additionally,
PETALUTE incorporates a golden-
angle rotation scheme, which intro-
duces temporal incoherence between
repetitions—enabling compressed
sensing reconstruction, retrospec-
tive temporal binning, and self-gated,
motion-resolved imaging (such as
respiratory or cardiac gating) with-
out requiring external hardware.
By combining multinuclear com-
patibility, UTE, and robust self-gating
features, PETALUTE creates a versatile
and high-quality platform for exam-
ining tissue microstructure, ionic
environments, and dynamic metabolic
activities, pushing the boundaries of
preclinical and translational MRI.
In contrast to traditional radial
and Cartesian or rosette schemes,
PETALUTE increases sampling den-
sity in two strategically important
regions of k-space: the center, which
enhances the SNR and supports self-
gated, motion-resolved imaging, and
the outer periphery, which improves
spatial resolution. Each petal read-
out starts and ends at the k-space
center, allowing two or more echoes
per repetition time. This inherent
multiecho setup allows for flexible,
interleaved contrast generation,
quantitative T2* mapping, and com-
pressed sensing-accelerated recon-
struction (Figure 2).
Implemented on Bruker’s preclini-
cal MRI platform, PETALUTE showed
significant improvements in imag-
ing efficiency and accuracy (Figure 3).
The sequence enables high-resolution
volumetric imaging with much shorter
scan times, while maintaining sensi-
tivity to rapidly decaying signals. By
capturing subvoxel contrast details
across large tissue volumes, PETA-
LUTE supports comprehensive evalua-
tion of microstructural and metabolic
changes with strong translational rel-
evance for neurological, musculoskel-
etal, and oncological studies.
Accurate Brain Imaging
A 2023 study published in Magnetic
Resonance in Medicine
4
demonstrated
the effectiveness of the PETALUTE
sequence in capturing signal compo-
nents with ultrashort transverse relax-
ation times in brain tissue—signals
that are usually inaccessible to conven-
tional
1
H MRI methods. Standard gra-
dient-echo and spin-echo sequences
are inherently biased toward long T2
components, resulting in poor sensi-
tivity for rapidly decaying structures,
such as tightly bound water pools,
macromolecules, or myelin.
PETALUTE, by contrast, operates at
echo times in the tens of microseconds,
enabling direct imaging of short-T2* spe-
cies. One of its most promising applica-
tions is visualizing the myelin bilayer—a
lamellar lipid structure that insulates
axons and is crucial for neural conduc-
tion and plasticity. Because myelin-
associated water signals decay rapidly,
traditional MRI sequences cannot cap-
ture its signal. PETALUTE’s multiecho
FIGURE 2
Multiecho brain imaging using the PETALUTE rosette trajectory acquisition. Coronal and
sagittal slices from a rodent brain scan demonstrate image quality across four echoes
acquired using the dual-repetition PETALUTE sequence. Data acquired from the UNC at
Chapel Hill’s BRIC.
IMAGE COURTESY OF PURDUE UNIVERSIT Y, INDIANAPOLIS, AND THE UNIVERSIT Y OF NORTH
CAROLINA AT CHAPEL HILL’S BIOMEDICAL RESEARCH IMAGING CENTER.
FIGURE 3
Multiecho PETALUTE fMRI: Echo-specific and combined activation maps during 1 Hz and 10
Hz visual stimulation.
10
IMAGE COURTESY OF PURDUE UNIVERSIT Y, INDIANAPOLIS, AND THE UNIVERSIT Y OF NORTH
CAROLINA AT CHAPEL HILL’S BIOMEDICAL RESEARCH IMAGING CENTER.
OCTOBER 2025 •WWW.RADIOLOGYTODAY.NET 29

3. UTE framework, combined with center-
out rosette sampling, allows reliable
detection and spatial localization of
myelin signal components.
In addition to
1
H-based applica-
tions, another recent study
5
highlighted
PETALUTE’s performance in
31
P MR
spectroscopic imaging (MRSI), where it
showed superior spatial coverage and
sensitivity compared with conventional
methods. This enables high-resolution
mapping of phosphorus-containing
metabolites such as adenosine tri-
phosphate (ATP) and phosphocre-
atine (PCr)—key indicators of cellular
energy metabolism—further expanding
PETALUTE’s potential in neurological,
oncological, and metabolic imaging.
This unique ability to detect ultrashort
T2* signals with high spatiotemporal
accuracy positions PETALUTE as a
transformative tool for microstructural
and metabolic brain imaging, with
significant implications for both basic
research and preclinical disease models.
Beyond the Brain
While initially developed for neuro-
imaging, the PETALUTE sequence
has demonstrated significant transla-
tional potential across multiple organ
systems, including musculoskeletal
and abdominal imaging, especially in
tissues characterized by rapid signal
decay, such as cartilage, bone, and liver.
By utilizing UTEs ranging from tens to
hundreds of microseconds, PETALUTE
enables the direct detection of short-T2*
components that are typically invisible
to conventional sequences.
One key application is osteoarthri-
tis, a degenerative joint disease affect-
ing over 528 million people worldwide,
according to the World Health Orga-
nization.
6
Early-stage osteoarthritis
involves the loss of glycosaminogly-
cans from cartilage. Sodium (
23
Na) MRI
provides a noninvasive way to measure
glycosaminoglycan content, but tra-
ditional sodium imaging faces chal-
lenges such as long scan times and low
spatial resolution. A clinical study in
Skeletal Radiology
7
showed that PETA-
LUTE enables in vivo sodium imag-
ing at 3 T with accuracy comparable
to standard methods, while reducing
scan time by 41%, and it enhances SNR
and central k-space sampling for better
spatial detail in thin cartilage layers.
Furthermore, PETALUTE has
proven effective in
31
P MRSI, where
rapid signal decay and low resolution
have historically limited the ability to
quantify metabolic intermediates such
as ATP, PCr, and inorganic phosphate. A
study by Bozymski et al
8
demonstrated
that PETALUTE achieves superior point
spread function, SNR, and acquisition
uniformity compared with traditional
31
P-MRSI approaches—advancing non-
invasive assessments of energy metabo-
lism in the brain and skeletal muscles.
Importantly, PETALUTE’s design
incorporates self-gating through
frequent central k-space sampling,
enabling retrospective motion cor-
rection in anatomies affected by
physiological motion, particularly
the abdomen, where respiration and
peristalsis commonly impair image
quality. This makes PETALUTE highly
suitable for imaging the liver, kidneys,
and gastrointestinal structures and
also supports its integration into
dynamic imaging protocols.
Specifically, PETALUTE facilitates
dynamic contrast-enhanced (DCE)
MRI, with its high temporal resolution
and multiecho setup enabling track-
ing of contrast kinetics in vascular and
perfusion studies. The sequence’s UTE
capabilities allow early-phase contrast
detection with enhanced sensitivity to
T1 changes, making it ideal for quan-
titative DCE studies in oncology, liver
fibrosis, and renal function evaluation.
In summary, the advances behind
PETALUTE, combining ultrashort TE
acquisition with efficient k-space sam-
pling, enable detailed multiparamet-
ric and multinuclear imaging across
various tissues for a wide range of bio-
medical applications. Its versatility in
supporting
23
Na,
31
P, and, potentially,
2
H
and
13
C imaging; resilience in motion-
prone contexts; and suitability for both
structural and DCE protocols establish
it as an all-in-one UTE platform for high-
impact translational research.
With robust preclinical results and
proven clinical feasibility, PETALUTE
bridges the gap between basic science
and clinical practice, supporting a uni-
fied approach to imaging fast-decaying
molecular signals, energy metabolism,
and perfusion dynamics. Its combina-
tion of motion resilience, multinuclear
capabilities, and dynamic imaging posi-
tions it as a next-generation framework
for both early-phase clinical studies and
mechanistic research in animal models.
The potential for PETALUTE to drive
discoveries in both clinical and preclini-
cal imaging is increasingly evident. As
adoption of this methodology expands
across the imaging research commu-
nity, PETALUTE is being integrated into
a growing range of applications, includ-
ing multiecho spectroscopic imaging,
balanced steady-state free precession
contrast strategies, and iron oxide
nanoparticle quantification in oncology
models. Its compatibility with a wide
array of pulse sequences and contrast
mechanisms, combined with its motion
resilience and rapid acquisition, makes
PETALUTE a versatile platform capable
of accelerating biomarker development
and translational imaging pipelines. By
enabling high-resolution, multinuclear,
and artifact-resistant imaging, PETA-
LUTE supports a new generation of non-
invasive tools for tackling global health
challenges through earlier diagnosis,
treatment monitoring, and mechanistic
insight across disease models. ■
Uzay Emir, PhD, recently joined the
University of North Carolina department of
radiology with a joint appointment in the
department of biomedical engineering. He
is a member of the Biomedical Research
Imaging Center as an associate professor
from Purdue University.
Stephen Sawiak, PhD, is a senior research
associate and fellow of Fitzwilliam College
of the University of Cambridge in the
United Kingdom.
MRI Monitor
!e potential for
PETALUTE to drive
discoveries in
both clinical and
preclinical imaging is
increasingly evident.
For references, view this article on our
website at www.RadiologyToday.net.
30!RADIOLOGY TODAY • OCTOBER 2025