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					     Measurements of 3He Diffusivity in Human Lung: Preliminary Results from an Emphysema Patient


                  B. Saam, D.A. Yablonskiy”4 D.S. Gieradab,J.D. Cooper”,and M.S. Conradi”’
                                   Radiology, and “Surgery, Washington University, St. Louis, MO, USA
           Departmentsof “Physics, ‘

INTRODUCTION                                                     RESULTS
     In addition to spin-densityimaging, studiesof T,* and            ADC maps are shown in Fig. 1 for a 23-year-old
difhtsivity of 3Hein the lung using hyperpolarized-3He   MRI     healthy male subject (left) and the emphysemapatient
have potential clinical use. Mugler, et ial.[l] have             (right) at the initial breathhold. The ADC in the healthy
               that
demonstrated 3Hedifhtsion in the gas-exchange          regions   lung is relatively uniform. Among the different healthy
of the human lung is restricted by the walls of the alveoli.     subjects, the mean ADC varies between 0.25 and 0.40
The apparent diffusion coefficients @DC’ measureds)              cm2/s,but there is little variation in mean ADC for the two
were 0.2-0.3 cm2/s, about four times smaller than what           slice locations and two breathholds in any given healthy
                    for
would be expected unrestricted      diffusion of dilute 3He in   subject. The ADC in the tracheafor all subjects is between
oneatm of air. Restricteddiffusion in the alveoli may have       0.9 and 1.0 cm2/s,much closer to the expectedvalue for
                                             the
implications for the study of emphysema: mean ADC                free diffusion of dilute 3He in air (= 1 cm2/s).
in emphysematous      lung should be greaterthan in healthy                    of
                                                                      Because severe      ventilationdefectsevident during the
lung and should increasewith diseaseseverity as the walls        initial breathhold,only about half of the relevant pixels in
of the alveoli deteriorate. One should also observe an           the emphysema-patient     imagecould be analyzed. The mean
increasein the width of the regional ADC distribution for        ADC in these regions is about 0.8 cm2Jswith a 20%
patients with inhomogeneous      disease. We present here        standarddeviation.
                                              in
preliminary results of ADC measurements both healthy
and emphysema-patient    volunteers usinghyperpolarized3He
MRI.

METHODS
                            of
     ADC measurements 3Hein the lung were made for
five healthy volunteers (ages 19-30 yrs) and one patient
volunteer with severeemphysema(female, age 71). The
patient volunteer was imaged several days prior to
undergoing lung-volume reduction surgery. All images
were acquired with a 1.5 T whole body scanner (Vision
Magneto% Siemens Medical Systems, Iselin, NJ),
operating at the 3He resonancefrequency of 48.47 MHz.            Fig. 1: ADC maps of a 10 mm coronal slice in (left) a 25-
The RF chest coil was a homebuilt transmit/receive               year-oldhealthymale volunteer (meanADC = 0.28 f 0.11
Hehnholtz pair.                                                  cm2/s) and (right) a 71-year-old female with severe
                      2-D                     was
      A conventional FLASH sequence modified to                  emphysema  (meanADC = 0.83 f 0.19 cm2/s).
collect four interleaved (line-by-line in k-space) coronal
imagesat eachof two slice locations(mid-anterior and mid-        DISCUSSION
posterior). TR = 89 ms, TE = 4.2, 11.7, 11.7, 24.2 ms, flip                                     in
                                                                     The meanADC measured the lung of the emphysema
angle= 5”. FOV = 400 x 400 mm on a 64 x 64 matrix. A             patient is a factor of two larger than eventhe largest value
dithtsion sensitizing                         to
                      gradientcorresponding b = 1.9 s/cm2        measured for a healthy subject. One may reasonably
was applied in the phase-encoding      direction (head-to-foot   interpret the ventilation defects (observed previously in
anatomically) for the third of the four images. (The first       emphysemapatients[2]) as correspondingto regions of
and fourth interleavedimages were additionally used in a         severe disease.Yet the present  ADC measurements    indicate
simultaneousmeasurement T,*.)  of                                alveolar breakdown in the ventilated regions as well. It is
      After obtaining informed consent,volunteersinhaled a       uncertain whether the ventilated regions represent more
mixture of approximately 0.5 L of 20-25% polarized 3He           severely diseasedareashaving greater complianceor less
and 1.5-2-O L of nitrogen (about 1.0 L for the patient           severely diseased areas with greater patency of small
volunteer). The two lo-mm thick slices were each acquired        airways. Better interpretations await more patient data and
                                   and
first duringthe initial breathhold then again after partial      comparisonto other imaging modalities such as X-ray CT
exhalation.(The emphysema       patient was unable to resume     to determinethe preciselocation of diseased   tissue.
breathhold   after partial exhalation.) Total acquisition time       It was thought that the ADC might correlatewith lung
for a data set was 26 s, including a 3 s break to allow for      volume and/or slice position (via the dependenteffect)
the partial exhale.                                              becauseof a correspondingchangein alveolar size. We
      Image data were analyzedfor 3He diffusion by taking        havethus far found no significant correlation. The reasons
the ratio pixel-by-pixel of image pairs acquired with and        for the large variation in mean ADC among the healthy
without diffusion sensitization at TE = 11.7 ms. Both a          subjectsare not well understood.
map and a histogram of regional ADC in each slice was
then generated. Pixels with signal intensities below an          REFERENCES
appropriate minimum threshhold or with ADC values                [l] Mugler, et al., Proc. 6” ISMRM, p. 1906 (1998).
outside a physically reasonablerange were not analyzed.          [2] Kauczor, et al., J. Magn. Reson. Imag. 7, 538, 1997.

				
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posted:2/29/2012
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