Respiratory Motion Reduction in PET/CT Using Abdominal Compression for Lung Cancer Patients
Kao C-H (2014) Respiratory Motion Reduction in PET/CT Using Abdominal Compression for Lung Cancer Patients. PLoS
ONE 9(5): e98033. doi:10.1371/journal.pone.0098033
Respiratory Motion Reduction in PET/CT Using Abdominal Compression for Lung Cancer Patients
Tzung-Chi Huang 0
Yao-Ching Wang 0
Yu-Rou Chiou 0
Chia-Hung Kao 0
Juri G. Gelovani, Wayne State University, United States of America
0 1 Department of Biomedical Imaging and Radiological Science, China Medical University , Taichung City, Taiwan , 2 Department of Biomedical Informatics, Asia University , Taichung City, Taiwan , 3 Department of Radiation Oncology, China Medical University Hospital , Taichung City, Taiwan , 4 Department of Nuclear Medicine, China Medical University Hospital , Taichung City , Taiwan
Purpose: Respiratory motion causes substantial artifacts in reconstructed PET images when using helical CT as the attenuation map in PET/CT imaging. In this study, we aimed to reduce the respiratory artifacts in PET/CT images of patients with lung tumors using an abdominal compression device. Methods: Twelve patients with lung cancer located in the middle or lower lobe of the lung were recruited. The patients were injected with 370 MBq of 18F-FDG. During PET, the patients assumed two bed positions for 1.5 min/bed. After conducting free-breathing imaging, we obtained images of the patients with abdominal compression by applying the same setup used in the free-breathing scan. The differences in the standardized uptake value (SUV)max, SUVmean, tumor volume, and the centroid of the tumors between PET and various CT schemes were measured. Results: The SUVmax and SUVmean derived from PET/CT imaging using an abdominal compression device increased for all the lesions, compared with those obtained using the conventional approach. The percentage increases were 18.1% 614% and 17% 616.8% for SUVmax and SUVmean, respectively. PET/CT imaging combined with abdominal compression generally reduced the tumor mismatch between CT and the corresponding attenuation corrected PET images, with an average decrease of 1.961.7 mm over all the cases. Conclusions: PET/CT imaging combined with abdominal compression reduces respiratory artifacts and PET/CT misregistration, and enhances quantitative SUV in tumor. Abdominal compression is easy to set up and is an effective method used in PET/CT imaging for clinical oncology, especially in the thoracic region.
Funding: This study was financially supported by National Science Council of Taiwan (NSC 102-2221-E-039-010-MY3) and by Taiwan Ministry of Health and
Welfare Clinical Trial and Research Center of Excellence (DOH102-TD-B-111-004). The funders had no role in study design, data collection and analysis, decision to
publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Respiratory motion causes image artifacts in PET/CT images
and misalignment between PET and CT. In PET imaging,
respiratory motion may give cause image blurring, degradation in
the image contrast, and an overestimation of the lesion volume. In
CT, respiratory motion may distort the tumor shape and volume
. In addition, when using CT images to correct for attenuation
in PET data, the mismatch between PET and CT images caused
by respiration may result in errors in localizing the tumor in PET,
leading to an inaccurate standardized uptake value (SUV) because
of the large difference in the acquisition time of CT and PET. An
overestimation of the volume and underestimation of the SUV of a
lung lesion caused by respiratory motion were reported by
Nehmeh et al and Erdi et al . Liu et al reported the
increased uncertainty of the SUV for lung tumors when
attenuation correction (AC) was performed using misaligned
PET/CT . Huang et al demonstrated that increased tumor
motion is closely associated with the SUV maximum (SUVmax)
decrease in patients with lung cancer . These artifacts and the
misalignment could cause potential misdiagnoses when combined
with the PET/CT imaging modality for lung cancer diagnosis .
Several techniques have been investigated to correct the PET/
CT misalignments and reduce artifacts to improve the quantitative
accuracy. The respiratory gating of PET and CT, in which the
collected data were binned into certain respiratory phases, was
used to reduce the motion artifacts and SUV errors . The
results of applying 4-dimensional (4D) PET/CT using 4D-CT
data with the gated PET images indicated improved lesion
registration and appropriate internal tumor volumes [1,9].
However, the long acquisition and processing time required to
conduct the examination was inevitable. The deep-inspiration
breath-hold technique has been proposed to improve the
inaccurate quantification of both SUVmax and metabolic volume,
but this method is not practical for all patients because it requires
patient compliance and may not be feasible for patients with
limited pulmonary function [6,10]. Cine average CT (CACT) was
proposed for AC in PET and the images exhibited considerably
less misalignments and artifacts compared with those obtained
using conventional helical CT (HCT)-based AC . The main
problem of CACT is that it requires the administration of a
relatively high radiation dose. Recently, the interpolated average
CT used for PET/CT AC corrected the PET/CT misregistration
and enhanced lesion quantitation accompanied by radiation
deduction. However, the complicated postimaging process is still
a concern regarding the use of these techniques in clinical practice
Abdominal compression is commonly used for reducing
thoracic tumor motion during treatment delivery in radiation
oncology. The use of abdominal compression for lung radiation
treatments efficiently reduces motion amplitude for lesions close to
the diaphragm . In this study, we demonstrated respiratory
motion correction in PET/CT by using an abdominal
compression device, and investigated the potential improvement of the
results compared with those produced using conventional CT
(HCT) on patients with lung cancer.
Materials and Methods
The current study was conducted from August 2013 to October
2013. Twelve patients (5 male, 7 female; average age, 60 years; age
range, 4377 years) with a diagnosis of lung cancer confirmed by a
physician at China Medical University Hospital were recruited.
The lung lesions had a size ranging from 3 to 44 cm. All the
patients who were selected had a tumor in the middle or lower
lobe of the lung, which are regions in which respiratory motion
clearly occurs. A summary of the clinical characteristics of the
patients is shown in Table 1. Written informed consent was
obtained from all the patients. All the data collection and analyses
performed in this study were approved by the Institutional Review
Board of China Medical University Hospital.
Imaging Acquisition Protocol
The patients were all injected with 370 MBq of 18F-FDG.
During the uptake phase that lasted for approximately 40 minutes,
the patients remained in a still position. The first whole-body
image was obtained when the patients were in a supine position
and the acquisition time per bed position was 1.5 min.
Freebreathing whole-body CT was conducted at 120 kV in helical
Right lower lobe
Right lower lobe
Right lower lobe
Right middle lobe
Right lower lobe
Right lower lobe
mode with a smart mA (range 30210 mA), 1.75:1 pitch, and 0.5-s
gantry rotation. For the thoracic PET, the patients assumed two
bed positions with 1.5 min/bed. After performing free-breathing
imaging (,5 min), we obtained images of the patients with
abdominal compression by using the same setup as that used in the
All the scans were acquired using a GE PET/CT-16 slice and a
Discovery STE (GE Medical System, Milwaukee, Wisconsin USA)
combined with an abdominal compression device (BodyFix
Diaphragm Control, Elekta) in 3-dimensional mode with
transaxial field-of-views (FOVs) of 70 and 50 cm for PET and CT,
respectively. The imaging protocol and the patient setup including
the abdominal compression device are shown in Figures 1a and
We used the same clinical reconstruction parameters for both
the free-breathing PET and abdominal-compression PET images.
The PETFB and PETab images were reconstructed using iterative
algorithms (Fourier rebinning and attenuation-weighted
orderedsubset expectation maximization, two iterations, 20 subsets, and a
6-mm Gaussian filter) and AC using HCT and
abdominalcompression CT (CTab), respectively. The data were reconstructed
using a 1286128 matrix and a 3-mm-thick slice. All the PET and
CT images were transferred to a GE workstation from which
fusion PET/CT images were constructed.
In the 3-dimensional (3D) PET/CT images, a 3D
volume-ofinterest (VOI) was manually drawn by an experienced physician
for each lesion in the PET images . The maximal value and
the mean SUV value in the VOI were defined as SUVmax and
SUVmean, respectively. The corresponding delineation of the VOI
in the CT images was performed by a radiation oncologist.
SUVmax was obtained for all lesions shown in the PETFB and
PETab images. The values of the SUVmax, SUVmean, and VOI
were compared. The continuous variables were expressed as the
mean 6 the standard deviation (SD). Statistical analyses were
conducted using the unpaired Students t test and paired t test. A P
value of ,0.05 was considered to be statistically significant. In
addition, the coordinates of the centroid of the lesion in the
PETFB, CT and PETab, and CTab images were determined based
on the chosen VOIs. The distances d between the tumor centroid
The SUVmax and SUVmean for all the tumors are summarized
in Table 2. The PETab image generally showed increased SUVmax
and SUVmean for all the lesions compared with those shown in the
PETFB image. The percentage increase (%diff) was 18.1% 614%
and 17% 616.8% for SUVmax and SUVmean, respectively. The
percentage difference of tumor volume in PET was in the range of
0.1% to 41%. PET/CT imaging combined with abdominal
compression generally reduced tumor mismatch d between the CT
image and the corresponding attenuation corrected PET images,
as shown in Table 2, with an average decrease of 1.961.7 mm
across all the tumors.
In Figure 2, the coronal views of the PETFB/CT and PETab/
CTab fusion images show the tumor in the right lower lobe for a
selected patient, Patient 4, who was used as a representative
example. Misalignment around the tumor (red arrow) was
observed in the PETFB/CT fusion images and the misalignment
was substantially improved in the PETab/CTab image, as shown in
Fig. 2(a) and Fig. 2(b), respectively. The values for PETab were
greater than those for PETFB by 8% and 13%. In addition, the
vertical profiles drawn in Fig. 2(c) demonstrate that the full width
at half maximum was smaller for the tumor shown in the PETab
image, indicating less blurring around the edges of the tumor in
the image, and a greater SUVmax was also easily observed in the
PETab image, thereby enabling more accurate and precise tumor
An abdominal compression device can be used to reduce lung
tumor motion . The efficiency of abdominal compression for
reducing lung tumor motion depends on the tumor location within
the lung. The significant effects of abdominal compression was
assessed by Bouilhol et al . The present study further
demonstrated that PET/CT imaging incorporating abdominal
compression potentially improved reconstructed PET image
quality and produces increased SUVs of the tumors and reduced
the respiratory artifacts containing spatial match in the PET and
CT fusion images. Several concerns that may arise are that the
increased SUV in the abdominal-compression images was caused
by abdominal compression, or that in reality, the SUV will
increase in active tumors with time postinjection because
abdominal-compression PET acquisition was performed after
conducting free-breathing PET acquisition on all of the patients.
However, the results of this study revealed that the mean PD of
SUVmax was 18%, which is too high to achieve time postinjection
on the tumor within less than 5 minutes. In addition, the
additional preparation time required to set up the abdominal
compression device was typically less than 5 minutes in our clinical
practice. Therefore, using the abdominal compression device for
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thoracic PET/CT acquisition is feasible for routine clinical use.
There are two concerns regarding the use of abdominal
compression: First, imaging combined with abdominal
compression may cause discomfort and possible anxiety for some patients
and is also unusable for obese patients. Second, abdominal
compression might be a potential source of increased tumor
motion variability, leading to inconsistencies in tumor delineation
during simulation CT for radiation treatment planning . To
solve this problem, concatenating the deformable image
registration to the abdominal compression is a possible option for linking
simulation CT and CTab for delineating tumors .
Several studies have reported that a decrease in SUV in 3D
PET scans is caused by the amount of displacement that occurs
and the pattern of respiration motion. The 4D PET scan can be
used to reduce the decrease in SUV induced by respiratory motion
[6,2122]. This study demonstrated that PET imaging combined
with abdominal compression device can also improve the SUV.
Increases in both the SUVmax and SUVmean for PETab compared
with those for PETFB were observed in this study. Tumors closer
to the diaphragm clearly moved with a large amplitude in the
superior-inferior direction; therefore, large SUVmax differences
between 4D PET and 3D PET scans exist and have been reported
in numerous studies. In this study, patient with tumors located in
the middle to lower lobes of the lung were recruited and the
SUVmax was successfully improved by approximately 7%54%.
The movement of the structures in the thorax is highly
correlated to the diaphragm motion that occurs during respiration
. This movement typically causes a larger tumor volume size
to appear in PET images, compared with the actual size of the
tumor, leading to PET/CT misalignment . The motion is
even more complex when the lesions are attached to the rigid
structure of the thorax, (eg, the pleura near the ribcage (Patients 3
and 10) and the diaphragm (Patient 5)). In this study, we observed
significant differences in the quantification results, which indicated
that the lesions attached to the rigid structure of the thorax
demonstrated large volume changes (Fig. 3) between the images
obtained with and without the use of abdominal compression.
However, the effects of using abdominal compression on the lesion
size, location, uptake ratio, and movement pattern are being
further investigated in our current study.
Figure 3. Percentage difference (PD %) in tumor volume derived from PET images of the patients.
We provided the preliminary results regarding the differences in
tumor motion caused by respiration in 12 lung cancer patients
imaged using an abdominal compression device, compared with
the images obtained using the conventional approach. The results
demonstrated that the reduction in overall PET image quality
resulted from respiratory motion and the mismatch between PET
and CT caused by using CT for AC in PET to incorporate the
abdominal compression device in PET/CT imagining.
Conceived and designed the experiments: TH YW. Performed the
experiments: TH YC. Analyzed the data: TH YW YC. Contributed
reagents/materials/analysis tools: CK. Wrote the paper: TH.
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