Radiopaque Marker Techniques

The most frequently used test for measurement of colonic transit involves radiopaque markers ingested in a medication capsule. In the original design of this method, a defined number of radiopaque markers were given orally at one time and excretion in the feces was monitored,30 thus providing an estimate of mouth-to-anus transit time. This approach is generally accepted as an inexpensive and suitable evaluation of total colonic transit, since the latter accounts for the major (but undefined) proportion of overall mouth-to-anus transit time.

This widely used method to quantify colonic transit has been modified by several groups,31-34 and the modifications are summarized in Table 7.4. An estimate of regional or segmental colonic transit is also obtained.34 For these purposes, radiopaque markers are given on several consecutive days in order to reach steady-state conditions, and abdominal radiographs are taken 4 days after the start of marker ingestion. In practice, a 7-day radiograph is also taken. The distribution of the markers in the right and left colon and rectosigmoid region provides some information about regional function. However, it must be emphasized that a disturbance in mechanics of defecation would also delay transit through one or more regions, irrespective of the method chosen. Hence, colonic transit data need to be interpreted with due consideration of other information, as discussed elsewhere in this book.

Table 7.4. Comparison of different radiopaque marker methods

Types of

Size range

Transit time

Transit normal (h)

Series

n

markers

(mm)

X-ray

calculated

(mean ± SD)

Hinton et al 196930

25

3

2.7-4.5 x 3

Stools, serially

Mouth to anus

95 percentile <66

1st marker in stool

95 percentile

80% markers in stool

<114

Cummings and

15

4

1.1 x 4.5

Stool, day 4

Mouth to anus

60.3 ± 3.6

Wiggins 197631

Single stool transit

(3-marker analysis)

Read et al 198013

14

1

2 x4

Stools, serially

Mouth to anus

48.5 ± 10.1

1st marker in stool

78.6 ± 15.1

50% markers in stool

100.3 ± 25.4

All markers in stool

Arhan et al 198132

37

1

3 x 6

Abdomen, serially

Colon

39 ± 5

(days 1-7)

Right colon

13

Left colon

15

Rectosigmoid

11

Chaussade et al

22

3

3 x 3 to 1 x 10

Abdomen, serially

Colon

34.4 ± 16.2

198633

(days 4,7,10)

Right colon

6.9 ± 7.8

Left colon

9.1 ± 10.3

Rectosigmoid

18.4 ± 12.5

Metcalf et al 198734

49

3

1 x 6 to 6 x 6

Abdomen, day 4

Mouth to anus

53.3 ± 3.7

Colon

35.0 ± 2.1

Right colon

11.3 ± 1.1

Left colon

11.4 ± 1.4

Rectosigmoid

12.4 ± 1.1

Bouchoucha et al

174

Several

Various

Abdomen, single and

Total

20.7 ± 1.9

199241

multiple

Counting the number of markers found in three segments of the large bowel (Fig. 7.5) has been useful in clinical practice to differentiate patients with constipation-predominant irritable bowel syndrome from those with colonic inertia or pseudo-obstruction who might benefit from subtotal colectomy with ileorectostomy.35-38 These methods are fairly reproducible in carefully selected patients (Fig. 7.6).

Using this method, investigators showed an association between colonic transit and stool consistency—hard stools were correlated with slow transit and loose stools with fast transit through the colon,39 suggesting a complementary role or utility of stool form scale (Bristol stool form scale) as a possible simple method of assessing intestinal transit rate.40

A simple approach is to ingest 20 markers on day 1 and take a radiograph on day 3. The presence of greater than eight markers remaining in the colon implies delayed colonic transit.41 Although one plain abdominal radiograph could sufficiently measure colonic transit at an acceptable radiation exposure, this technique would not be applicable in motor disturbances associated with accelerated colonic transit. To identify and quantitate accelerated transit, earlier,

Colon Transit Radiopaque
Figure 7.5. Abdominal radiograph showing radiopaque markers in three segments of colon: right, left, and rectosigmoid.
0 25 50 75 100 125

Second MCTT, hr

Figure 7.6. Reproducibility of radiopaque marker method in patients with severe idiopathic constipation.Note that one patient has a great discrepancy in measured colonic transit time (MCTT) on two occasions, approximately 1 year apart.

Table 7.5. Comparison of methods for measurement of colonic transit

Method

Advantages

Disadvantages

Precautions

Radiopaque markers Scintigraphy

"VDTPA liquid transit

Simple, inexpensive, and reproducible No increased radiation exposure with increased number of scans Simple

Follow emptying of liquid throughout gut Noninvasive

Identifies onset of colonic transit Labels solid phase No preparation needed Applicable for fast or slow transit

Day 4 x-ray may miss transit profile Needs gamma camera

Needs gamma camera

Supplement diet with 10g fiber Radiation exposure acceptable

Radiation exposure acceptable

Delayed-release capsule

5% failure of capsule dissolution 1 hour preparation of materials

Requires use of 111In to measure prolonged transit in constipation

Adapted from von der Ohe M, Camilleri M. Measurement of small bowel and colonic transit; indications and methods. Mayo Clin Proc 1992;67:1169-1179.

repeated radiographs would be necessary, thereby increasing the radiation exposure. This simple test is easy to follow; thus, patients can easily be given instructions to perform the test at home and mail the radiographs to a referral center during follow-up. Table 7.5 compares the advantages and disadvantages of both radiopaque marker and scintigraphic tests.

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Constipation Prescription

Constipation Prescription

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