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\begin{document}

\title{Diffusion MRI of Parathyroid Adenomas using a Distortion Reduction
Scheme}



\author[1]{Hirotaka Yamamoto}%
\author[2]{Mami Iima}%
\author[2]{Yo Kishimoto}%
\author[2]{Ayami Kishimoto}%
\author[2]{Sho Koyasu}%
\author[2]{Akira Yamamoto}%
\author[2]{Yoshitaka Kawai}%
\author[2]{Akira Yoshizawa}%
\author[3]{Koichi Omori}%
\affil[1]{Tenri Hospital}%
\affil[2]{Kyoto University Graduate School of Medicine Faculty of Medicine}%
\affil[3]{Kyoto University}%


\vspace{-1em}



  
  \date{May 28, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
Objectives: To evaluate whether readout-segmented echo-planar imaging
(RS-EPI) diffusion-weighted imaging (DWI) can reduce image distortion
and improve the lesion identification in parathyroid adenomas (PTAs)
compared to single-shot EPI (SS-EPI) DWI, and to determine whether PTAs
can be differentiated from other soft tissue structures of the head and
neck region by using the apparent diffusion coefficient (ADC) value.
Design: Retrospective study. Setting: Kyoto University Hospital.
Participants: 24 patients who underwent a magnetic resonance imaging
(MRI) scan for the preoperative diagnosis of PTAs from January 2012 to
March 2020 were enrolled. Main outcome measures: MRI was performed with
the acquisition of a 1.5T MR imaging system (Avanto or Trio, Siemens,
Erlangen, Germany) or a 3T MR imaging system (Prisma or Skyra, Siemens).
Image quality and distortion of PTAs on RS-EPI and SS-EPI was evaluated
using a reported five point score, and the ADC values of PTAs, thyroid
glands and cervical neck lymph nodes were compared. Results: RS-EPI
provided significantly less distortion but did not improve the lesion
identification compared to SS-EPI. On SS-EPI, the PTAs had significantly
higher ADC values compared to the cervical lymph nodes. On RS-EPI, the
PTAs had significantly higher ADC values compared to the thyroid glands
and cervical lymph nodes. Conclusions: RS-EPI reduces the DWI distortion
in PTAs. The ADC value obtained using RS-EPI enables the differentiation
of PTAs from nearby structures, such as thyroid glands and cervical
lymph nodes.%
\end{abstract}%



\sloppy


\textbf{Article type:} Original Article

\textbf{Abstract}

\textbf{Objectives:} To evaluate whether readout-segmented echo-planar
imaging (RS-EPI) diffusion-weighted imaging (DWI) can reduce image
distortion and improve the lesion identification in parathyroid adenomas
(PTAs) compared to single-shot EPI (SS-EPI) DWI, and to determine
whether PTAs can be differentiated from other soft tissue structures of
the head and neck region by using the apparent diffusion coefficient
(ADC) value.

\textbf{Design} : Retrospective study.

\textbf{Setting} : \begin{CJK}{UTF8}{gbsn}〈\end{CJK}\selectlanguage{english}Blinded for review\begin{CJK}{UTF8}{gbsn}〉

\end{CJK}\selectlanguage{english}\textbf{Participants} : 24 patients who underwent a magnetic resonance
imaging (MRI) scan for the preoperative diagnosis of PTAs from January
2012 to March 2020 were enrolled.

\textbf{Main outcome measures} : MRI was performed with the acquisition
of a 1.5T MR imaging system (Avanto or Trio, Siemens, Erlangen, Germany)
or a 3T MR imaging system (Prisma or Skyra, Siemens). Image quality and
distortion of PTAs on RS-EPI and SS-EPI was evaluated using a reported
five point score, and the ADC values of PTAs, thyroid glands and
cervical neck lymph nodes were compared.

\textbf{Results:} RS-EPI provided significantly less distortion but did
not improve the lesion identification compared to SS-EPI. On SS-EPI, the
PTAs had significantly higher ADC values compared to the cervical lymph
nodes. On RS-EPI, the PTAs had significantly higher ADC values compared
to the thyroid glands and cervical lymph nodes.

\textbf{Conclusions:} RS-EPI reduces the DWI distortion in PTAs. The ADC
value obtained using RS-EPI enables the differentiation of PTAs from
nearby structures, such as thyroid glands and cervical lymph nodes.

\textbf{Keywords:} parathyroid adenoma, readout-segmented echo-planar
imaging, diffusion-weighted-MRI, apparent diffusion coefficient

\textbf{Wordcount main article:} 2278

\textbf{Key points:}

\begin{itemize}
\tightlist
\item
  The Kappa values between the two readers revealed
  substantial-to-perfect agreement.
\item
  RS-EPI provided significantly less distortion compared to SS-EPI,
  however the structure identification scores were not significantly
  different from SS-EPI.
\item
  The PTAs exhibited relatively high signal intensity on DW-MRI with
  either SS-EPI or RS-EPI.
\item
  On SS-EPI, the PTAs had significantly higher ADC values compared to
  the cervical lymph nodes.
\item
  On RS-EPI, the PTAs had significantly higher ADC values compared to
  the thyroid glands and cervical lymph nodes.
\end{itemize}

\textbf{Introduction}

Primary hyperparathyroidism (PHPT) is a clinical condition characterized
by elevated serum parathyroid hormone (PTH), followed by increased serum
calcium (Ca). Patients with PHPT frequently manifest symptoms such as
hypercalcemia, anorexia, nausea, and nephrocalcinosis. The treatment for
PHPT used to be a total parathyroidectomy, but PHPT is usually caused by
a single parathyroid adenoma (PTA)(1, 2), and selective
parathyroidectomy has been recently preferred for the treatment of
single adenomas as a less invasive option(3, 4). For a successful
selective parathyroidectomy, accurate imaging techniques are required
for the preoperative localization of PTAs. Ultrasonography and
technetium 99mTc-sestamibi scintigraphy have often been accepted as
first-line imaging to localize PTAs. When first-line imaging fails to
localize the parathyroid lesion, or PHPT is recurrent or persistent
after surgery, computed tomography (CT) and magnetic resonance imaging
(MRI) are considered as second-line imaging techniques (1, 5). Recently,
the multiphasic CT (4D CT) has made it possible to identify PTAs through
their hypervascular perfusion pattern compared with lymph nodes and
thyroid gland(5), however CT has the disadvantage of ionizing radiation.

MRI has the advantage of lack of ionizing radiation, and with the
introduction of high field magnetic systems, the use of MRI for the
localization of parathyroid adenomas has been re-assessed as a
supplemental imaging modality. The sensitivity of 1.5T MRI for the
detection of PTAs was reported to be 43\%--71\%(6-8), but since 3T
scanners were introduced into clinical practice in the early 2000s, the
higher signal-to-noise and contrast-to-noise ratios have improved the
sensitivity of MRI to 97.8\%.(1) However, some limitations remain
because the MR appearance of PTAs overlaps considerably with those of
cervical lymph nodes and an ectopic thyroid gland, which leads to
difficulties in distinguishing PTAs from other structures in the neck.

The measurement of the apparent diffusion coefficient (ADC) value in
diffusion-weighted imaging (DWI) has been reported to be helpful in
distinguishing parathyroid tissues from other soft-tissue structures of
the head and neck region.(9) Single-shot echo-planar imaging (SS-EPI)
has been the most widely used DWI sequence, but SS-EPI suffers from
susceptibility artifacts which manifest as geometric distortion and
image blurring,(10) and the detection of PTAs by DWI thus remains
challenging. To overcome this weakness, readout-segmented echo-planar
imaging (RS-EPI) was developed; with this imaging modality, there is a
substantial reduction in the distortion and blurring caused by T2* decay
during the readout(11, 12). RS-EPI is expected to improve the diagnostic
accuracy of detecting PTAs on DWI as it provides less distortion, and
its advantages are reported in some organs including the head and
neck(13-15).

However, to our knowledge, there is no literature focusing on the
usefulness of RS-EPI for the localization and distinction of PTAs. We
conducted the present retrospective study to determine whether RS-EPI
can reduce image distortion and improve the lesion identification in
PTAs compared to SS-EPI, and to determine whether PTAs can be
differentiated from other soft-tissue structures of the head and neck
region by using the ADC value.

\textbf{Materials and Methods}

\emph{MRI examination}

The MRI examinations in this study were performed with a 1.5T MR imaging
system (Avanto or Trio, Siemens, Erlangen, Germany) or a 3T MR imaging
system (Prisma or Skyra, Siemens). The parameters for the DWI sequences
are summarized in \textbf{Table 1} .

\emph{Setting and Participants}

This study was approved by the institutional review board of \begin{CJK}{UTF8}{gbsn}〈\end{CJK}\selectlanguage{english}Blinded
for review\begin{CJK}{UTF8}{gbsn}〉. \end{CJK}\selectlanguage{english}A total of 34 patients with PTA who underwent an MRI
examination for the preoperative diagnosis of PTA at \begin{CJK}{UTF8}{gbsn}〈\end{CJK}\selectlanguage{english}Blinded for
review\begin{CJK}{UTF8}{gbsn}〉 \end{CJK}\selectlanguage{english}during the period from January 2012 to March 2020 were
examined. SS-EPI at 1.5T was performed in eight patients during the
period Jan. 2012 to Nov. 2017, and RS-EPI at 3.0T was performed in 26
patients during the period July 2014 to March 2020. All patients
underwent a parathyroidectomy, and the resected specimens were
histologically evaluated. Of the 34 patients, 10 patients were excluded
from this study for the following reasons: the lesion was not detectable
on MRI (n=3), DWI data were obtained using a different protocol (n=5),
and the presence of severe motion or susceptibility artifacts (n=2). The
remaining 24 patients were enrolled. Their clinical information
including the results of imaging examinations was retrospectively
reviewed.

\emph{Analysis of image quality and distortion}

Board-certified radiologists A and B independently evaluated the image
quality and the distortion of parathyroid lesions on DWI. They had
access to other MR images (T2- or T1-weighted images or STIR image) for
a reference. They were informed that the DWIs were acquired for the
preoperative evaluation of PTA, and they were unaware of any other
radiologic information. Structural identification and geometric
distortion were evaluated using a reported five-point scale (Table
2).(13)

\emph{Measurements of ADC values}

ADC measurements of the lesions were performed on the ADC map that
contained the largest lesion cross-section, using circular
regions-of-interest (ROIs) with a mean area of 10 mm\textsuperscript{2}.
Each ROI was carefully drawn within the solid part of the lesion to
exclude artifacts and areas of cyst and/or necrosis. The ADC values of
each patient's cervical lymph nodes and thyroid glands were also
measured.

\emph{The DWI statistical analysis}

The inter-observer variability between the wo radiologists was evaluated
using inter-rater agreement (Kappa coefficient). As described,(16) the
results were interpreted as follows: values [?]0 indicate no agreement;
0.01--0.20 indicate none to slight agreement, 0.21--0.40 = fair
agreement, 0.41--0.60 = moderate, 0.61--0.80 = substantial, and
0.81--1.00 = almost perfect agreement.(17) The ADC values of the
parathyroid lesions, thyroid glands, and cervical lymph nodes were
analyzed using the Friedman test with Bonferroni correction, and the
scores of structure identification and geometric distortion on SS-EPI
and RS-EPI were compared using the median test. In both tests, p-values
\textless{}0.05 were accepted as significant. All statistical analyses
were performed with EZR (Saitama Medical Center, Jichi Medical
University), which is a graphical user interface for R (The R Foundation
for Statistical Computing, Vienna, Austria, ver. 2.13.0).(18)

\textbf{Results}

\emph{Patients and lesions}

The patient and lesion characteristics are summarized in \textbf{Table
3} . The SS-EPI group was two males and six females (mean age 64 years,
range 48--76 years), and the RS-EPI group was six males and 10 females
(mean age 55.6 years, range 25--80 years). All lesions were
pathologically diagnosed as parathyroid adenomas, and there were no
significant differences in patient or lesion characteristics between the
two groups.

\emph{Assessments of structure identification and distortion}

The Kappa values between the two readers revealed substantial-to-perfect
agreement (structure identification provided by SS-EPI: 0.73, distortion
by SS-EPI: 1, identification by RS-EPI: 0.75, distortion by RS-EPI:
0.82). The mean scores of structure identification and geometric
distortion for SS-EPI and RS-EPI by the two readers are shown
in\textbf{Table 4} . The distortion scores for RS-EPI were significantly
higher than those for SS-EPI (all p-values were \textless{}0.05),
indicating lower distortion, and the image quality provided by RS-EPI
was better than that obtained with SS-EPI. However, the results of the
median test of the structure identification scores were not
significantly different between SS-EPI and RS-EPI.

\emph{Representative cases}

Representative cases of SS-EPI and RS-EPI are shown in \textbf{Figures
1} and \textbf{2} . A 67-year-old female was diagnosed as having a PTA
of the right inferior gland and presented high intensity mass on STIR;
however, there was considerable distortion on SS-EPI (Fig. 1). In
contrast, in the case of a 72-year-old female with a PTA at the left
inferior gland with DWI using RS-EPI, the lesion was identified with
less distortion (Fig. 2).

\emph{Discrimination of PTAs from the thyroid gland and cervical lymph
nodes using ADCs}

The PTAs exhibited relatively high signal intensity on DW-MRI with
either SS-EPI or RS-EPI, with high ADC values. On SS-EPI, the average
ADC values of the PTAs, thyroid glands, and cervical lymph nodes were
1.44, 1.07, and 0.80 \selectlanguage{ngerman}×\selectlanguage{english} 10\selectlanguage{english}\textsuperscript{-3} mm\textsuperscript{2}/s,
respectively, and a significant difference between the PTAs and lymph
nodes was observed. Moreover, the average ADC values of the PTAs,
thyroid glands, and cervical lymph nodes were 1.67, 1.46, and
0.95\selectlanguage{english} x\selectlanguage{english} 10\selectlanguage{english}\textsuperscript{-3} mm\textsuperscript{2}/s on RS-EPI, and the
PTAs exhibited significantly higher ADC values compared to those of the
thyroid glands and lymph nodes (Fig. 3).

\textbf{Discussion}

We evaluated the clinical utility of DWI for the pre-operative
localization of PTAs. While the PTAs were faintly identified with
intense distortion on SS-EPI, they were fairly identified with moderate
distortion on RS-EPI. The inter-rater reliability was substantial or
perfect, and the validity of DW-MRI for the localization of PTAs was
demonstrated. In addition, the PTAs could be discriminated from cervical
lymph nodes and thyroid glands by measuring the ADC values, and thus
RS-EPI is expected to become the optimal diagnostic modality for the
localization of PTAs.

With the introduction of 3T MRI, improved diagnostic performance for the
detection of PTAs has been reported in relation to the higher spatial
resolution and contrast-to-noise ratio.(1) PTAs are usually T2
hyperintense, and fat suppression is effective to achieve an accurate
depiction.(1) However, fat suppression is not easy to use in the neck
region, especially in the mediastinum, because of the magnetic field
inhomogeneities due to the proximity of lungs and upper airways. It thus
remains challenging to obtain good images of PTAs with MRI, and there is
currently no consensus on the optimal MRI protocol for the evaluation of
PTAs.

The diagnostic value of 4D MRI and of the IDEAL sequence for the
detection of PTAs has been reported.(19, 20) Although the use of these
imaging techniques improved the diagnostic sensitivity for the detection
of PTAs, false-positive diagnoses are occasionally attributed to
cervical lymph nodes or adjacent/ectopic thyroid tissues. To distinguish
PTAs from lymph nodes and thyroid tissues, Yildiz et al. used
conventional DWI provided by a 1.5T system, and they reported higher ADC
values in parathyroid lesions compared to lymph nodes and thyroid
tissues; however, the statistical significance of these differences was
not reported.(9)

Although SS-EPI is a well-established conventional method for the
acquisition of DWI data with short scan times, it suffers from geometric
distortion, signal dropout, and image blurring. Alternatively, RS-EPI is
a multi-shot sequence that reduces susceptibility artifact and blurring
arising from T2* decay, and thus lower distortion can be achieved.(21)
The clinical utility of RS-EPI has been well documented in some regions,
including the head and neck.(13) In our present case series, the
acquisition parameters were quite different between RS-EPI and SS-EPI,
because they were independently set to optimize their image quality
within clinically acceptable acquisition times (2--3 min). Since a
sufficient signal-to-noise ratio (SNR) was not expected for SS-EPI, the
number of excitations were increased to four. A sufficient SNR was
expected for RS-EPI, so we increased the number of readout segments to
five, to reduce the distortion. The results demonstrated that the PTAs
were well identified with less distortion by RS-EPI compared to SS-EPI,
and the conclusions of the two independent readers showed a good
correlation.

RS-EPI is thought to be a useful and reliable imaging technique for the
evaluation of PTAs. However, we observed herein that even with RS-EPI,
some PTAs were poorly identified with intense distortion, which might
mask the improvement in the lesion identification score. The distortion
might come from (1) the relatively large field of view (FOV) needed to
obtain whole neck images, (2) susceptibility artifact that remained even
with RS-EPI, and/or (3) motion artifact from respiration. In addition,
it is not still easy to obtain good-quality DW images at the upper
mediastinum due to the complex stricture facing the air, and the
establishment of a feasible imaging protocol of the cervical region to
the upper mediastinum using DW-MRI is expected.

In this study, we used ADC values for discriminating the PTAs and other
cervical organs, and the PTAs were well distinguished from the thyroid
glands and cervical lymph nodes. Cervical lymph nodes exhibit low ADC
values,(22) and benign neck pathologies including adenomas are reported
to show relative high ADC values,(23, 24) which is consistent with our
present observations. Higher ADC values were observed on RS-EPI compared
to SS-EPI in our case series. Differences in ADC values between RS-EPI
and SS-EPI are still controversial. Although higher ADC values on RS-EPI
have been reported in the human mammary gland and in a phantom
study,(21, 25) Koyasu et al. reported no significant differences in the
ADCs of salivary gland lesions.(13) In our present cases, the accurate
evaluation of lesions due to less distortion on 3T RS-EPI may have
contributed to the precise selection of the area, while more distorted
lesions on 1.5T SS-EPI might have been contaminated by surrounding fat
tissue and consequently resulted in a decreased ADC, which we observed
particularly in the thyroid glands. Adding DWI using RS-EPI to common
sequences such as STIR and T2WI could thus be beneficial for the
pre-operative evaluation of PTAs.

This is the first study to investigate the clinical utility of RS-EPI in
the pre-operative localization of PTAs, to our knowledge. One of the
limitations of our study was its retrospective design. In addition, the
acquisition protocols for SS-EPI and RS-EPI were independently set to
maximize their own features (rather than a comparison of the two
protocols), which resulted in different acquisition schemes. The sample
size was small, and there would be a selection bias because selected
patients with surgically confirmed pathologies were included. Further
prospective studies with larger sample sizes are warranted to clarify
the diagnostic utility, indications, and limitations of RS-EPI for the
localization of PTAs.

\textbf{Conclusion}

Our study demonstrated that RS-EPI produces images with less DWI
distortion than SS-EPI, which may provide clinical advantages in the
localization of PTA. And PTAs have higher diffusion properties compared
with thyroid glands, and cervical lymph nodes using RS-EPI. This feature
enables us to the differentiation of PTAs from nearby structures on MRI.

\textbf{References}

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\textbf{Table 1.} Parameters for DWI\selectlanguage{english}
\begin{longtable}[]{@{}lll@{}}
\toprule
& \textbf{SS-EPI (1.5T)} & \textbf{RS-EPI (3T)}
\textsuperscript{\textbf{++}}\tabularnewline
\midrule
\endhead
b-value, sec/mm\textsuperscript{2} & 0, 1000 & 0, 1000\tabularnewline
FOV & 180*180 & 211*220\tabularnewline
Matrix & 192*192\textsuperscript{+} & 142*148\tabularnewline
TR & 5900 & 4100\tabularnewline
TE & 81 & 54\tabularnewline
Slice thickness, mm & 4 & 3\tabularnewline
Fat suppression & STIR & SPAIR\tabularnewline
Averages & 4 & 1\tabularnewline
Acquisition time, min:sec & 2 & 2:15\tabularnewline
\bottomrule
\end{longtable}

\textsuperscript{+}The matrix for SS-EPI is
interpolated.\textsuperscript{++}Five readout segments are used. FOV:
field of view.

\textbf{Table 2.} Scales for structure identification and geometric
distortion on DWI (modified from ref. 13)

Scales for structural identification\selectlanguage{english}
\begin{longtable}[]{@{}ll@{}}
\toprule
4 & Excellent: Perfectly demarcated contour and very good contrast with
surrounding structure\tabularnewline
3 & Good: Almost good contour, but partially (\textless{}50\%) mixed
with the background\tabularnewline
2 & Fair: Organ/node can be discriminated from surrounding structures,
while more than half of the contour is mixed with the
background\tabularnewline
1 & Faint: Structures of organ/nodes are ill-defined, but can be
identified by faint contrast with surrounding structures\tabularnewline
0 & Unidentifiable: Cannot identify any structures\tabularnewline
Scales for geometric distortion & Scales for geometric
distortion\tabularnewline
4 & High geometric accuracy and almost no distortion\tabularnewline
3 & Faint distortion: Organ/node slightly tilts, but its convexity is
almost the same as that of T2-weighted turbo spin-echo sequence (TSE)
image\tabularnewline
2 & Moderate distortion: Convexity is less pronounced or lost compared
to that of a T2-weighted TSE image\tabularnewline
1 & Intense distortion: Convexity is opposite compared to that of a
T2-weighted TSE image, or severe dislocation exists\tabularnewline
0 & Impossible to evaluate, or unidentifiable\tabularnewline
\bottomrule
\end{longtable}

\textbf{Table 3.} Patient and lesion characteristics\selectlanguage{english}
\begin{longtable}[]{@{}llll@{}}
\toprule
& \textbf{SS-EPI} & \textbf{RS-EPI} & \textbf{p-value}\tabularnewline
\midrule
\endhead
No. of patients & 8 & 16 &\tabularnewline
Sex & & & 0.667\tabularnewline
Male & 2 & 6 &\tabularnewline
Female & 6 & 10 &\tabularnewline
Mean age (range), years & 64.0 (48--76) & 55.6 (25--80) &
0.191\tabularnewline
Location of lesion & & &\tabularnewline
Right superior & 1 & 4 &\tabularnewline
Right inferior & 2 & 5 &\tabularnewline
Left superior & 1 & 0 &\tabularnewline
Left inferior & 4 & 7 &\tabularnewline
Size of lesion, mm & 19.3(10--25) & 19.0 (8--30) & 0.92\tabularnewline
Comparisons between the SS-EPI and RS-EPI were performed by Chi-square
test for sex, and by median test for age and size of lesion. &
Comparisons between the SS-EPI and RS-EPI were performed by Chi-square
test for sex, and by median test for age and size of lesion. &
Comparisons between the SS-EPI and RS-EPI were performed by Chi-square
test for sex, and by median test for age and size of lesion. &
Comparisons between the SS-EPI and RS-EPI were performed by Chi-square
test for sex, and by median test for age and size of
lesion.\tabularnewline
\bottomrule
\end{longtable}

\textbf{Table 4.} Evaluation of structural identification and geometric
distortion using a five-point scale\selectlanguage{english}
\begin{longtable}[]{@{}llllllll@{}}
\toprule
& \textbf{Reader 1} & \textbf{Reader 1} & \textbf{Reader 1} & &
\textbf{Reader 2} & \textbf{Reader 2} & \textbf{Reader 2}\tabularnewline
\midrule
\endhead
& \textbf{SS-EPI} & \textbf{RS-EPI} & \textbf{p-value} & &
\textbf{SS-EPI} & \textbf{RS-EPI} & \textbf{p-value}\tabularnewline
Identification of structure & 1.63\selectlanguage{ngerman}±0.92 & 2.44\selectlanguage{ngerman}±1.09 & 0.085 & &
1.50\selectlanguage{ngerman}±0.93 & 2.38\selectlanguage{ngerman}±1.02 & 0.054\tabularnewline
Geometric distortion & 1.38\selectlanguage{ngerman}±0.92 & 2.38\selectlanguage{ngerman}±0.96 & 0.023* & & 1.38\selectlanguage{ngerman}±0.92 &
2.38\selectlanguage{ngerman}±0.89 & 0.017*\tabularnewline
Data are mean \selectlanguage{ngerman}± SD. Comparisons between SS-EPI and RS-EPI were performed
by median test. *p\textless{}0.05. & Data are mean \selectlanguage{ngerman}± SD. Comparisons
between SS-EPI and RS-EPI were performed by median test.
*p\textless{}0.05. & Data are mean \selectlanguage{ngerman}± SD. Comparisons between SS-EPI and
RS-EPI were performed by median test. *p\textless{}0.05. & Data are mean
\selectlanguage{ngerman}± SD. Comparisons between SS-EPI and RS-EPI were performed by median
test. *p\textless{}0.05. & Data are mean \selectlanguage{ngerman}± SD. Comparisons between
SS-EPI and RS-EPI were performed by median test. *p\textless{}0.05. &
Data are mean \selectlanguage{ngerman}± SD. Comparisons between SS-EPI and RS-EPI were performed
by median test. *p\textless{}0.05. & Data are mean \selectlanguage{ngerman}± SD. Comparisons
between SS-EPI and RS-EPI were performed by median test.
*p\textless{}0.05. & Data are mean \selectlanguage{ngerman}± SD. Comparisons between SS-EPI and
RS-EPI were performed by median test. *p\textless{}0.05.\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{ngerman}



\textbf{Figure Legends}

\textbf{fig. 1.} Representative SS-EPI images of a 67-year-old female
with primary hyperparathyroidism. \textbf{A:} STIR: A high-intensity
mass on STIR was detected behind the right lobe of the thyroid
gland.\textbf{B:} DWI with SS-EPI: A faint high-intensity lesion on DWI
was detected in the corresponding location on STIR. The image was scored
to be impossible to evaluate by two readers. \textbf{C:} ADC map: A high
value was detected on the ADC map. The lesion was diagnosed as a PTA of
the right superior gland. A 21\selectlanguage{english} x\selectlanguage{english} 16\selectlanguage{english} x\selectlanguage{english} 17 mm PTA was confirmed at surgery

\textbf{Fig. 2.} Representative RS-EPI images of a 72-year-old female
with primary hyperparathyroidism. \textbf{A:} STIR: A high-intensity
mass on STIR was detected behind the left lobe of the thyroid
gland.\textbf{B:} DWI with RS-EPI: A high-intensity lesion on DWI was
detected in the corresponding location on STIR. The lesion was evaluated
as showing almost no or faint distortion. \textbf{C:} ADC map: A high
value was detected on the ADC map. The lesion was diagnosed as a PTA of
the left inferior gland. A 28\selectlanguage{english} x\selectlanguage{english} 22\selectlanguage{english} x\selectlanguage{english} 5 mm PTA was confirmed at surgery

\textbf{Fig. 3.} The ADC values of the parathyroid lesions, thyroid
glands, and cervical lymph nodes. \emph{Left:} SS-EPI.
\emph{Right:}RS-EPI. *p\textless{}0.05\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Fig1/Fig1}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Fig2/Fig2}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Fig3/Fig3}

\end{center}
\end{figure}

\selectlanguage{english}
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\end{document}

