Kiyohisa Kamimura1, Masanori Nakajo1, Yoshihiko Fukukura1, Takashi Iwanaga2, Tomonori Saito2, Masashi Sasaki2, Takuro Fujisaki2, Atsushi Takemura3, Tomoyuki Okuaki 3, and Takashi Yoshiura1
1Radiology, Kagoshima University Medical and Dental Hospital, Kagoshima, Japan, 2Clinical Engineering Department Radiation Section, Kagoshima University Hospital, Kagoshima, Japan, 3Philips Electronics Japan, Tokyo, Japan
Synopsis
Our purpose was to evaluate the
feasibility of intravoxel incoherent motion (IVIM) assessment based on turbo
spin-echo diffusion-weighted imaging (TSE-DWI) in the normal pituitary gland.
In a validation study using normal brain white matter (WM), Bland-Altman
analyses revealed fair to good agreement with conventional echo-planar-based
DWI (EP-DWI) in the true diffusion coefficient (D) and perfusion fraction (f).
In 7 volunteers, both D and f in the anterior pituitary lobe were significantly
higher than those in WM, being consistent with high microvascular density in
the pituitary gland. Results demonstrated that IVIM assessment based on TSE-DWI
in the pituitary gland is feasible.PURPOSE
The intravoxel incoherent motion (IVIM)
imaging is an advanced diffusion-weighted imaging (DWI) technique that allows
for a separate quantitative evaluation of all the microscopic random motions
that contribute to DWI, which are essentially represented by molecular
diffusion and blood microcirculation (perfusion)
1). Single-shot
echo-planar (EP)-DWI is most commonly used for IVIM imaging. However, EP-DWI is
associated with strong susceptibility artifacts that cause image distortions in
the skull base, making it difficult, if not impossible to measure the IVIM
parameters in the anterior pituitary lobe accurately. Turbo spin-echo (TSE)-DWI
was reported to mitigate such problems in the skull base and sinonasal cavities
2). The purpose of this study was to evaluate the feasibility of IVIM assessment
based on TSE-DWI in the normal anterior pituitary lobe.
MATERIALS and METHODS
First, we performed
an in-vitro experiment for validation of TSE-DWI sequence on a GDTPA-doped
water phantom by comparing the signal decay according to b values between
EP-DWI and TSE-DWI using the concordance correlation coefficient (CCC). The
imaging conditions were as follows: 3T MR imager and a 15-channel receiver head
coil; TR/TE 3,000/52 ms; flip angle 90°; 3 MPG directions; FOV 180 mm; imaging
matrix 100 x 100; number of excitations 6. We used13 different b values (0, 10,
20, 30, 50, 80, 100, 200, 300, 400, 600, 800, and 1,000 s/mm
2). A 3
mm-thick sagittal slice was placed. Second, in-vivo validation study for IVIM
based on TSE-DWI was conducted using 5 healthy volunteers. For the TSE-DWI
sequence, peripheral pulse triggering was utilized to reduce signal variability
due to CSF pulsation (resultant TR 2,400-3,000 ms). For each subject, an
additional IVIM imaging based on conventional EP-DWI was performed for
comparison. The true diffusion coefficient (D), perfusion fraction (f), and
pseudo-diffusion coefficient (D*) were calculated by fitting the IVIM model to
the measured signal changes for each voxel. Agreement of D, f, and D* measured
with the 2 methods in 4 regions-of-interests (ROIs) in the brain white matter
(WM) regions (pons, vermis, and genu and splenium of the corpus callosum) was
assessed using the Bland-Altman plot. Finally, the three IVIM parameters (D, f,
and D*) in the anterior pituitary lobe were compared with those in the 4 ROIs
in the WM using Dunnett's test in 7 healthy volunteers.
RESULTS
The phantom experiment
revealed complete accordance in the signal decay between EP-DWI and TSE-DWI
(CCC>0.9999). In all subjects, TSE-DWI visualized the pituitary gland with
acceptable image distortion (Fig. 1). The Bland-Altman analysis showed that the
agreement between TSE-DWI and EP-DWI was good (95% limits of agreement ranged
from -0.1086 to 0.0786 x10
-3 mm
2/s) for D, fair (-5.03 to
4.32 %) for f, and poor (-8.41 to 5.79 x10
-3 mm
2/s) for
D* (Fig. 2). No obvious systematic bias was shown for any parameter. The mean D
(x10
-3 mm
2/s) in the normal
anterior pituitary lobe was 0.960±0.097, which was significantly higher than
those in the pons (0.711±0.024), vermis (0.666±0.027), and genu (0.699±0.042)
and splenium (0.749±0.038) of the corpus callosum (P < .001, respectively. Fig.
3A). The f (%) in the normal anterior pituitary lobe was 13.15±2.37, which was
significantly higher than those in the pons (5.56±1.45), vermis (3.94±1.36),
and genu (5.32±1.24) and splenium (5.15±1.00) of the corpus callosum (P <
.001, respectively. Fig. 3B). The D* (5.81±2.15 x10
-3 mm
2/s)
in the normal anterior pituitary lobe was not significantly different from
those in the pons (5.96±2.75), vermis (3.75±3.02), and genu (7.72±1.32) and
splenium (5.35±2.39) (Fig. 3C), which may be due to high variability.
DISCUSSION
and CONCLUSION
Our results for the agreement showed that IVIM
assessment based on TSE-DWI can provide similar information regarding D and f,
but not D* to that provided by conventional EP-DWI. Moreover, the values of D
and f in the brain WM measured with TSE-DWI were in good agreement with previously
published values obtained with EP-DWI
3) .The normal anterior
pituitary lobe was shown to have higher f than the brain WM, which is
consistent with high histological microvascular density in the anterior
pituitary lobe
4). Taken together, our study suggests that IVIM assessment based on TSE-DWI in the
normal anterior pituitary lobe is feasible. It may be useful
to characterize pituitary lesions such as microadenoma.
Acknowledgements
No acknowledgement found.References
1. Le Bihan D, et
al. MR imaging of intravoxel incoherent motions: application to diffusion and
perfusion in neurologic disorders. Radiology 1986;161(2):401-7.
2. Raya JG, et al. Methods
and applications of diffusion imaging of vertebral bone marrow. J Magn Reson
Imaging 2006;24(6):1207-20.
3. Federau C, et al.
Measuring brain perfusion with intravoxel incoherent motion (IVIM): initial
clinical experience. J Magn Reson Imaging 2014;39:624-32.
4. Vidal S, et al. Vascularity
in nontumorous human pituitaries and incidental microadenomas: a morphometric
study. Endocr Pathol 2000;11(3):215-27.