DOI:10.2214/AJR.04.1812
AJR 2005; 185:1180-1184
© American Roentgen Ray Society
Effect of Adjusted Positioning on Gastric Distention and Fluid Distribution During CT Gastrography
Se Hyung Kim1,
Jeong Min Lee1,2,
Joon Koo Han1,2,
Jae Young Lee1,2,
Han Kwang Yang3,
Hyuk-Joon Lee3,
Kyung-Sook Shin4 and
Byung Ihn Choi1,2
1 Department of Radiology, Seoul National University Hospital, 28, Yongon-dong,
Chongno-gu, Seoul 110-744, Korea.
2 Institute of Radiation Medicine, Seoul National University Hospital, Seoul,
Korea.
3 Department of Surgery, Seoul National University Hospital, Seoul, Korea.
4 Department of Radiology, Chungnam National University Hospital, Daejeon,
Korea.
Received November 23, 2004;
revised January 10, 2005;
Address correspondence to J. M. Lee
(leejm{at}radcom.snu.ac.kr).
Abstract
OBJECTIVE. We hypothesized that performing CT gastrography with the
patient in the left posterior oblique (LPO) position would provide better
distention and less residual fluid for the lower part of the stomach than CT
gastrography with the patient in the standard supine position.
CONCLUSION. The LPO position for CT guaranteed the distensibility of
and minimal residual fluid in the lower part of the stomach, thus resulting in
excellent 3D CT gastrographic images.
Introduction
With the recent advances in MDCT technology, the use of 3D applications to
examine the gastrointestinal tract, such as CT colonography, CT enterography,
and CT gastrography, is dramatically increasing. Optimizing patient
preparation for gastrointestinal tract CT examinations is an important
consideration to increase the performance of CT in various diagnostic fields.
In particular, in the field of CT colonography, there has been considerable
interest in achieving better preparation including maximizing distention,
minimizing residual fluid or feces, patient positioning, use of hypotonia, and
optimal choice of inflating agent (room air or carbon dioxide)
[1–4].
By comparison, the necessity for refining CT gastrography techniques has been
unnoticed. The recent popularity of minimally invasive surgery, such as
laparoscopy-assisted gastrectomy, has required accurate 3D reconstruction of
the stomach and its surrounding structures to avoid complications caused by a
limited field of view during laparoscopic surgery. Moreover, at many
institutions, 3D CT gastrographic images, including surface-shaded or
transparent volume-rendered images, have decreased the need for conventional
double-contrast barium studies for global assessment of gastric diseases.
In previous 3D CT studies of the stomach performed with the patient in the
supine or prone position, tumors located at the antrum were not well
delineated because of poor stomach distention or fluid retention
[5,
6]. To circumvent this problem,
we performed CT gastrography with the patient in the 30° left posterior
oblique (LPO) position, which we defined as the CT LPO position. We
hypothesized that performing CT gastrography with the patient in the LPO
position would provide better distention of and less residual fluid in the
lower part of the stomach than performing the examination with the patient in
the standard supine position.
Materials and Methods
From February to July 2004, 85 consecutive patients with pathologically
proven early gastric cancer (57 men, 28 women; mean age, 59 years; age range,
39–78 years) who underwent CT gastrography were enrolled in our study.
Eighty-five early gastric cancers were identified on histopathology. Among
them, 40 lesions were confined in the mucosal layer and the remaining 45
lesions in the submucosal layer. The lesions were located on the fundus in
three patients, the upper body in 10, the lower body in 20, the proximal
antrum in 24, and the distal antrum in 28 patients. According to the
morphologic classification, 45 of the 85 lesions were classified as early
gastric cancer type IIc; 10 as stage I; seven each as IIa + IIc and stage IIc
+ IIa; four each as stage IIa, IIb + IIc, and stage IIb + IIa; and two each as
stage IIa + IIb and III.
Before CT examination, 10 mg of butyl scopolamine (Buscopan, Boehringer
Ingelheim) was administered IV to decrease bowel peristalsis and to facilitate
hypotonia. Then, to attain gastric distention, two packs of effervescent
granules with minimal water (< 5 mL) were administered orally while the
patient was on the CT table just before scanning. CT was performed using a
16-MDCT scanner (Sensation 16, Siemens Medical Systems). The CT parameters
used were as follows: 120 kVp, 100 effective mAs, 16 x 0.75 mm detector
configuration, 15 mm/sec table feed (beam pitch of 1.25), and 1-mm
reconstruction with 30% overlap.
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Fig. 1A —CT gastrographic images of 64-year-old man in left posterior
oblique (LPO) position. Axial CT scan obtained with patient in 30° LPO
position for distention of distal half of stomach shows markedly distended
lower body (arrowhead) and distal antrum (arrow) without any
residual fluid within those segments. Grade 4 (> 75%) was assigned to those
three segments with regard to both distention and residual fluid.
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Fig. 1B —CT gastrographic images of 64-year-old man in left posterior
oblique (LPO) position. 3D CT gastrography images resulting from use of
surface-shaded (B) and transparent (C) volume-rendering
technique show good distention of stomach except in gastric fundus. Note
bubbly fluid (arrow, B) in fundus.
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Fig. 1C —CT gastrographic images of 64-year-old man in left posterior
oblique (LPO) position. 3D CT gastrography images resulting from use of
surface-shaded (B) and transparent (C) volume-rendering
technique show good distention of stomach except in gastric fundus. Note
bubbly fluid (arrow, B) in fundus.
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The patients were randomly allocated into one of two groups according to
the intended scanning position. The first group (n = 52) included
patients undergoing CT in the CT LPO position. For this position, patients
were first positioned in the left lateral decubitus position to shift the
gastric contents from the lower two thirds to the fundus of the stomach; they
were then immediately placed on the scanning table in a 30° LPO position
by placing a pillow at their back
[7] (Fig.
1A,
1B,
1C). The second group of
patients (n = 33) included those who underwent CT in the standard
supine position (Fig. 2A,
2B,
2C). Each scan was completed
within 12–17 sec. CT images regardless of scanning position were
obtained 70 sec after injection of 120 mL of nonionic contrast material
(iopromide [Ultravist 370, Schering]) at a rate of 3–4 mL/sec. CT
gastrographic images were created using a surface-shaded and transparent
volume rendering technique by experienced 3D technicians using dedicated 3D
software (Rapidia, Infinitt).
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Fig. 2A —CT gastrographic images of 48-year-old man in standard supine
position. CT scans obtained with patient in standard supine position show
distal antrum (arrow, A) is severely collapsed and contains
substantial amount of fluid within that segment; it was assigned grade 1 (<
25%) for both parameters. Note also slightly collapsed proximal antrum with
small amount of fluid (arrow, B). Grade 3 (51–75%) was
assigned to this segment regarding residual fluid.
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Fig. 2B —CT gastrographic images of 48-year-old man in standard supine
position. CT scans obtained with patient in standard supine position show
distal antrum (arrow, A) is severely collapsed and contains
substantial amount of fluid within that segment; it was assigned grade 1 (<
25%) for both parameters. Note also slightly collapsed proximal antrum with
small amount of fluid (arrow, B). Grade 3 (51–75%) was
assigned to this segment regarding residual fluid.
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Fig. 2C —CT gastrographic images of 48-year-old man in standard supine
position. 3D CT gastrography image resulting from use of surface-shaded
volume-rendering technique shows severely collapsed gastric antrum
(arrow). This image provides only suboptimal quality for evaluation
of that segment.
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Two reviewers evaluated the CT gastrographic data in consensus for the
degree of gastric distention and the presence of residual fluid. For the sake
of recording data, the stomach was divided into five segments—that is,
the fundus, upper body, lower body, proximal antrum, and distal antrum.
Gastric distention and residual fluid were ranked on a 4-point scale. Gastric
distention was recorded as 1 for less than 25% of the expected maximal luminal
dimension, grade 2 for 25–50%, grade 3 for 51–75%, and grade 4 for
more than 75%. Residual fluid in a gastric segment was measured relative to
the maximum anteroposterior diameter of the segment: grade 1 for an
air–fluid level greater than 50% of the maximum anteroposterior diameter
of the segment; grade 2 for 25–50%; grade 3 for 1–25%; and grade 4
for no residual fluid (Figs.
1A,
1B,
1C and
2A,
2B,
2C). The two groups were
compared using the Mann-Whitney U test with respect to the two
parameters. A p value of less than 0.05 was considered to indicate a
statistically significant difference.
Results
The total grades for the two parameters to determine the adequacy of CT
gastrography are summarized in Table
1 with the p values of the intergroup statistical
analysis. For statistical analysis, scores of both gastric distention and
residual fluid were averaged and assigned a total score.
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TABLE 1: Gastric Distention and Residual Fluid Grades Assigned to Images Obtained
with Patients in the Left Posterior Oblique (LPO) Position Compared with Those
Assigned to Images Obtained with Patients in the Supine Position and
Comparative Statistical Analysis
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In terms of gastric distention, the mean scores for most of the segments
were larger in the LPO group than in the supine group. The differences between
the mean scores of the two groups were statistically significant in the lower
three segments—that is, the lower body, proximal antrum, and distal
antrum (p < 0.004). Regarding residual fluid, the mean scores for
the proximal and distal antrum were significantly larger in the LPO group than
in the supine group (p < 0.03). For the remaining three segments,
the mean scores in the LPO group tended to be larger than those for the supine
group, but these differences were not statistically significant (p
> 0.05). For the LPO group, the total scores averaged for both parameters
were significantly higher than for the standard group in the lower three
segments (p < 0.002). For the LPO group, the total score averaged
for all five segments in both parameters was 3.6 ± 0.8 (mean ±
SD), but was 3.2 ± 1.0 for the supine group. The difference was also
statistically significant (p < 0.0001). Representative examples
are shown in Figures 1A,
1B,
1C and
2A,
2B,
2C.
Discussion
In this study, CT gastrography with the patient in the LPO position
provided better gastric distention and less residual fluid in the lower part
of the stomach than CT gastrography with the patient in the conventional
supine position. On double-contrast barium study, it is well known that images
obtained with the patient in the LPO position give an excellent
double-contrast view of the distal half of the stomach
[8]. In addition to good
distention, no residual fluid should be retained for CT gastrography because
if residual fluid is present, clinically important lesions could potentially
be obscured due to interference from the proper lumen–wall interface
caused by the administration of effervescent agents.
Unlike double-contrast barium studies in which imaging can be performed in
multiple projections to allow the fluid to redistribute, scanning for CT
gastrography should be limited to only one or two projections—that is,
the supine or LPO position and the right decubitus position. As shown in the
Results section, positioning toward one's back in the LPO position just after
turning onto one's left side can shift fluid in the gastric antrum to the
gastric fundus and subsequently allow a clean image of the lower gastric
portion to be obtained.
The combined interpretation of axial and 3D volume-rendered images in CT
gastrography is necessary to make an accurate diagnosis by allowing viewing of
the intraluminal morphology and extraluminal characteristics of various
gastric diseases [7]. In
addition, during preoperative planning, accurate localization of the lesion is
as important as tissue characterization. Conventional gastroscopy is extremely
sensitive for gastric mucosal lesions. However, additional studies, such as
double-contrast barium study or CT, are frequently needed to perform the full
structural examination and to evaluate extraluminal conditions preoperatively.
In the 3D volume-rendered images we used, simultaneous evaluation of the local
and the global views is possible during a single examination. These images
allow the surgeon to perform preoperative planning including accurate
localization. This information is more important for laparoscopy-assisted
gastric surgery due to the lack of information usually obtained on tactile
assessment. Therefore, appropriate preparation—that is, good distention
and minimal fluid for the distal half of the stomach in which most of lesions
occur—is necessary to obtain good CT gastrographic images.
Several limitations of this study should be mentioned. First, we were not
able to determine the exact volume of the residual fluid present within
gastric segments at the time of CT gastrography. However, we think that our
method for quantifying residual fluid provides a reasonable representation of
the relative amounts. Second, because the position of the patients on the CT
couch is obviously visible on the 2D CT gastrographic data set, the reviewers
could not be totally blinded to scanning position. Third, although our results
showed that the LPO position is helpful in obtaining good distention and
minimal residual fluid for the gastric lower portion, it cannot be applied for
the gastric upper portion. Theoretically, the evaluation of the fundus and the
cardia would be potentially limited in both the LPO and standard supine
positions. Therefore, further studies regarding the effect of other positions,
such as the right decubitus or prone position, on the adequate preparation of
the gastric upper portion will be needed.
Finally, the objective of our study was not to evaluate the diagnostic
performance of CT gastrography for detecting gastric lesions. Rather, our goal
was to evaluate the feasibility of CT gastrography with the patient in a new
position to achieve better gastric distention with less residual fluid
compared with studies performed with the patient in the supine position.
Although our initial results seem to be promising, further prospective studies
with larger numbers of patients will be needed to assess the diagnostic
performance of CT gastrography with the patient in the LPO position and to
confirm the feasibility of performing CT gastrography with the patient in the
LPO position.
In conclusion, CT with the patient in the LPO position guarantees
distention of the lower part of the stomach and retention of minimal residual
fluid in the lower part of the stomach, thereby resulting in excellent 3D CT
gastrographic images.
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Abstract
Introduction
