Radiographic Positioning of the Large Intestine

Radiographic Positioning of the Large Intestine


In this presentation, we will be reviewing
the positioning criteria for the large intestine as it relates to the performance of barium
enemas. Barium Enema Series consists of these typical
views: Routine views include: PA and/or AP Sigmoid RAO and LAO LPO and/or RPO Lateral rectum R and L lat decub (double-contrast) Cross table lateral rectum PA postevac Special views include: AP axial or AP axial oblique (Sigmoid) PA axial or PA axial oblique (Sigmoid) Upright positions Positioning for upright positions are the
same as for recumbent, except IR is placed slightly lower to compensate for drop of anatomy PA Large Intestine: Position the patient prone. The CR enters at the level of the iliac crests
at the MSP. Use 14 x 17 collimation and expose on suspended
expiration. The entire colon should be visualized. Here we can see the difference between double-contrast
on the left, single contrast in the middle, and a post-evacuation image on the right. You’ll notice variation in shape of the
large intestine between patients radiographically as well. Keep this in mind during the fluoroscopic
routine to help you adjust positioning appropriately for these overhead images to include the entire
colon. AP Large Intestine: The positioning criteria
is the same as for the PA with two distinct differences. The patient is supine of course, but also,
place the table in slight Trendelenberg position to aid in contrast retention. When viewing your radiographs for quality
control, make sure to check for rotation with the bony anatomy such as the wings of the
pelvis and vertebral column, and ensure the entire colon is visualized. From the top, the splenic flexure is usually
most superior. Some patients with hypersthenic body habitus
may also need crosswise IR placement. If that’s the case, then one upper abdomen
and one lower abdomen exposure may be required for the AP, PA and/or Obliques. PA Axial Large Intestine: This view can be
performed AP or PA. Here we’ll look at the PA method. Angle the CR 30-40 degrees caudad and center
midline to the level of the ASIS. Use a 10×12 collimated field, and make sure
to include the rectosigmoid colon. This view provides less superimposition of
the sigmoid and rectum over each other than the straight AP or PA views. This view should include the entire sigmoid
colon, all the way down to the rectum, with the balloon visible inferiorly on the radiograph. Notice how the extreme angle elongates the
bony structures of the pelvis. For the AP Axial Large Intestine, you will
need to apply the same 30-40 degree angulation to the x-ray tube, only cephalic this time,
with the patient supine. Center midline approximately 2 inches below
the ASIS, restricting the beam to a 10×12 field. This provides a similar view of the rectosigmoid
colon free of superimposition, and the superior portions of the colon (ascending, descending
and transverse) are not required to include on this view. Though the image on the left is one of the
textbook examples, collimation could have been applied to a greater degree here. The image on the right is more appropriate
to visualize the necessary anatomy. Notice how much of the pelvis is visible on
the right compared to nearly the entire pelvis and large intestine (minus the superior portion
of the splenic flexure) on the left. For the Oblique Large Intestine, this can
be done anteriorly or posteriorly. Practice the entire BE routine views as a
series, and find out what works best for you, considering what may be easiest for the patient
each time. I personally prefer the LPO view, but the
RAO will demonstrate the same anatomy. Consult your departmental routine for double-contrast
studies as contrast displacement will be different between LPO and RAO views. The patient should be rotated between 35 and
40 degrees either way, with the central ray directed 1-2 inches lateral to midline toward
the elevated side at the level of the iliac crest. Collimate to a 14 x 17 field to include the
entire colon. This view should demonstrate the right colic,
or hepatic flexure in profile, as well as the ascending colon free of superimposition
and the sigmoid colon. Let’s take a look at these single-contrast
images. There’s a significant difference between
the position of the transverse colon between these images. Remember, the transverse colon curves anteriorly
from the hepatic flexure to midline, then starts curving posteriorly again as it leads
toward the splenic flexure. We’ll give you a great study tool to remember
this structure in lab this week, but you will need to remember this in order to determine
which oblique to perform to demonstrate each portion of the colon, as well as the flexures. Here we see some double-contrast views. Notice how the contrast is distributed differently
between the RAO view on the left and the LPO view on the right. Another detail to note is how far away from
midline the colon extends in the oblique position. The textbook CR states 1-2 inches lateral
from midline, however, with hypersthenic patients with large abdomens, the CR may need to be
adjusted more laterally. You can see in the image on the left that
the descending colon and splenic flexure are closer to the edge of the IR. Also note that there is similarity on the
patient’s right, regardless of patient size, showing that the ascending colon typically
doesn’t move far left-to-right from the bony landmark of the ASIS. You should always make sure the exposure field
on the patient’s right side includes the ASIS to ensure you don’t clip anatomy. Looking at the opposite oblique, we can utilize
the same criteria for the LAO and RPO views, rotating the patient 35-45 degrees and centering
1-2 inches lateral to midline toward the up-side. This view will best demonstrate the left colic,
or splenic flexure and the descending colon free of superimposition. One common positioning error performed with
these obliques, that also applies to the lumbar spine, is unequal rotation between the shoulders
and hips. I find that using a 45 degree wedge sponge,
supporting both shoulders and hips, is a great way to make sure you are not over or under
rotated when comparing these two sections. Again we have the single contrast views of
the LAO on the left and the RPO on the right. While we’re primarily looking for the splenic
flexure to be in profile here, you can also note the position of the pelvis, which should
be pretty close to the oblique lumbar spine. You can also see the scotty dogs, and can
apply knowledge of over/under rotation for the spinal anatomy here. After a few exams, you’ll begin to notice
that even if scotty dogs are visible, the flexures will vary in demonstration with body
habitus, sometimes requiring more or less rotation compared to the bony anatomy. And again we see the LOA and RPO comparisons
with double-contrast. These views should be performed based on where
the radiologist would like to see the contrast distributed, while the single-contrast views
are selected more for patient comfort and/or technologist’s preference since the contrast
looks the same. For the lateral rectum, the patient needs
to be placed in the true lateral position with knees bent. Hips and shoulders should be perpendicular
to the table with the pelvis lateral. The CR enters the midcoronal plane at the
level of the ASIS. This view can be performed for both single
and double-contrast exams, however, sometimes the double-contrast exam calls for a cross-table
lateral, which I’ll cover next. Regardless of patient position, a 10 x 12
field of view can be used. I’m a huge supporter of collimation for
this view since the field of view lies so close to the genitals. Keep in mind the rectum does not extend superior
of L5, so you can place the top of your light field around the iliac crest. It also lies just anterior to the sacrum,
so simply include the sacrum in your collimated field. Inferiorly, if you collimate to the anus where
the visible enema tip is protruding, you will never clip the anatomy. The cross-table lateral is not included in
the textbook, but it is popular for double-contrast routines and would typically be the last view
to perform once you’ve identified all of your other images do not require repeats or
additional views. Essentially the positioning criteria is the
same with the patient prone, however, some routines require removal of the enema tip
immediately before exposing the image. Make sure to have all of your equipment set
up with a receptacle nearby for when you remove the enema tip, along with some towels for
the patient. Set up your technical factors at the control
panel, align your x-ray tube and image receptor, and instruct the patient that you are going
to deflate the balloon and remove the tip, and they need to attempt to hold in the contrast
as much as possible for a few seconds to obtain the exposure. When ready, deflate the balloon and toss the
bag and tip into the receptacle, then make your exposure. As soon as you can, return to the patient
and provide them with a towel to take care of any leakage, then escort them to the restroom
to evacuate. You can use this time to clean your x-ray
table if needed and prepare for your post-evac image if required. The other views you may be required to perform
include lateral decubitus images. These views are only performed during double-contrast
studies and timing is key. If you are going to perform them at the end
of your overhead routine, the air sometimes dissipates and you may need to ask the radiologist
if additional air needs to be added. For this reason, I like to perform them at
the beginning of the overhead routine, but again, do what works for you… there’s no perfect order for every situation,
but many things to consider. For the right lateral decubitus, the patient
is in right lateral position with radiolucent support if needed under the abdomen. Center to the MSP at the level of the iliac
crests with a horizontal beam. Place your marker on the up-side. This view displays the medial aspect of the
ascending colon and lateral aspect of the descending colon. The idea is that the best-demonstrated portions
are those that have been coated by contrast, but filled with air. Remember, contrast is going to follow gravity,
so the up-side of each portion of the colon will be demonstrated. For the left lateral decubitus, the positioning
criteria is the same, although the CR may be entering posteriorly. Don’t forget to change your marker on the
image receptor and mark the up-side. Center to the MSP at the level of the iliac
crest and include the entire colon. This view demonstrates the lateral aspect
of the ascending colon and the medial aspect of the descending. The textbook shows the decubitus views hung
as-shot, however, I’ve seen some radiologists who prefer this versus some who prefer these
images to be hung in the anatomical position. Make sure you know which way is preferred
for the radiologists you work with. Occasionally, a double-contrast routine may
call for upright views to demonstrate the transverse colon. While these are more rare to perform, keep
in mind when centering whether or not you are required to include the entire colon or
just the transverse for your routine. Also remember that the colon may migrate inferiorly
with gravity in the upright position. After the overhead views have been completed
and you have verified that no additional views are required by the radiologist, a PA or AP
Postevac film may be requested. This should be positioned the same way a KUB
is positioned, but with high kVp as used with contrast studies. Center to the MSP at the level of the iliac
crests and expose on suspended expiration. Include the entire large intestine. The patient should be encouraged to evacuate
as much as possible prior to this image, and they make take a little bit of time in the
restroom before coming back out. As previously stated, you can be cleaning
your x-ray table, the exam room, documenting pertinent details about the procedure, or
annotating your previous views while the patient is in the restroom, but don’t forget to
check on the patient frequently, keeping in mind that this exam is physically exerting
and they have been NPO on top of it. There’s risk for dizziness and fatigue at
the end of the exam. I also find that having a clean gown, 2-3
towels and 2-3 wash cloths already in the restroom for the patient is helpful. This is typically part of my room setup before
the procedure, but they should be encouraged to clean all of the barium off their skin,
and to change gowns if any barium leaked on their first one. Excess barium that was spilled can cause unwanted
artifacts on your images, and the patient really doesn’t want to continue on with
soiled linen at this point. As a side note, when the post-evac image is
complete, the patient should be informed that they should be drinking plenty of water to
flush out any remaining barium, and to expect their stool to be chalky in appearance. If they experience constipation that an over-the-counter
laxative doesn’t resolve, they need to contact their physician.

Leave a Reply

Your email address will not be published. Required fields are marked *