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 10x12 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 10x12
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.