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1
Division of Abdominal Imaging and Interventional Radiology, Ellison 234,
Massachusetts General Hospital, Boston, MA 02114.
2
Present address: Department of Medical Imaging, Toronto General Hospital, 200
Elizabeth St., Toronto, Ontario, M5G 2C4 Canada.
3
Decision Analysis and Technology Assessment (DATA) Group, Massachusetts
General Hospital, Zero Emerson PI., Ste. 2H, Boston, MA 02114.
Received September 15, 1999;
accepted after revision December 15, 1999.
Address correspondence to M. E. O'Malley.
Abstract
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MATERIALS AND METHODS. The survey was distributed to 70 members (36 institutions) of the Society of Computed Body Tomography/Magnetic Resonance. The survey included general questions related to abdominal and pelvic helical CT and also asked the members to write a protocol for 12 hypothetical requisitions.
RESULTS. Thirty-two members (46%) responded, representing 28 institutions (78%). The number of protocols for helical CT of the abdomen and pelvis at each institution ranges from 2 to 35 (median, 11). IV contrast material is administered for 90% (median) of abdominal and pelvic CT examinations. Nonionic contrast material is used for 68% (median) of these examinations. IV contrast material is used by 100% of institutions for tumor staging protocols except for one institution that does not use IV contrast material for lymphoma staging. Fifty percent of the institutions obtain two- or three-phases of liver images for breast cancer staging. For all protocols, the average collimation and reconstruction interval is 7 mm except for renal (5 mm) and adrenal (4 mm) protocols. Rectal contrast material is administered most commonly for colon cancer staging (39% of institutions).
CONCLUSION. There is a wide range in the number of protocols used for helical CT in the abdomen and pelvis among the responding institutions. Most protocols include use of nonionic IV contrast material injected at a rate of 3 ml/sec and a collimation of 7 mm.
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Instructions mailed with the surveys asked that the survey be completed by the designated Society of Computed Body Tomography/Magnetic Resonance member, the radiologist responsible for abdominal and pelvic CT protocols at the institution, or the chief CT technologist. The survey asked the respondent general questions including the following: the number of active CT protocols; the percentage of examinations performed with IV contrast material; the percentage of examinations performed using nonionic IV contrast material; the number of helical CT scanners at the institution; whether cases were checked by a radiologist before the patient left the radiology department or the scanning suite; and whether the institution had CT scanners that were dedicated to imaging specific organ systems.
The survey included 12 hypothetical requisitions and the respondents were asked to provide details about how such patients would be scanned at their institution. The hypothetical requisitions were as follows: breast cancer staging, colon cancer staging, lymphoma staging, prostate cancer staging, other cancer staging, evaluate renal mass, evaluate adrenal mass, renal colic, abdominal pain, rule out abscess, rule out diverticulitis, and rule out appendicitis. For each requisition, the respondent was instructed to assume that this was the first radiologic study for the patient at their institution, the patient had no allergies, the patient's renal function was normal, no further information about the patient was available, and the study was to be performed on the institution's most frequently used helical CT scanner.
For each hypothetical requisition, the respondent was asked to provide the following scanning parameters: scan mode, collimation (mm), reconstruction interval (mm), use of oral contrast material, use of rectal contrast material, use of IV contrast material, volume of IV contrast material injected (ml), rate of IV injection (ml/sec), and scan delay after IV injection (sec). For scan mode, the options were conventional, helical, or combined. These responses are reported as "% helical" in Tables 1,2,3; this figure represents the percentage of institutions that chose helical or combined for "scan mode." For the use of oral contrast material, the result was recorded as "yes" if either standard radiopaque contrast material or water was used. For the use of rectal contrast material, the result was recorded as "yes" if standard radiopaque contrast material, water, or air was administered rectally. Below the list of scanning parameters, a space was left for "comments."
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For purposes of statistical analysis, numeric results were rounded to the first decimal point and the results are reported to the nearest whole number. If the respondent indicated a range of numbers for a given parameter, the mean value was used for analysis. Data were analyzed using software (SAS Institute, Cary, NC). The Student's t test was used to compare continuous data, and the chi-square test was used to compare categoric data. A correlation was made between the number of protocols used and the number of helical scanners at each institution; the use of IV contrast material at institutions that did and those that did not check examinations before patients left the department; and the frequency of nonionic contrast material use and the frequency of IV contrast material administration.
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The median number of helical CT scanners at each institution is three (range, 1-12). At 14 institutions (50%), the scans are routinely checked while the patient is still on the table. At 11 institutions (39%), the scans are not routinely reviewed before the patient leaves the department, and at the other three institutions (11%), only certain examinations are checked before the patient leaves the department. Twenty-three institutions (82%) have scanners that are used for all organ systems on an as-needed basis, whereas two institutions (7%) have devoted specific scanners to one or more particular organ system (e.g., chest or abdomen).
Six institutions (21%) commented that they use a computer-assisted, automated technique such as Smartprep (General Electric Medical Systems, Milwaukee WI) for timing the delivery of IV contrast material for at least one of their protocols or for certain patients (e.g., patients with decreased cardiac output).
One institution (4%) calculates the volume of IV contrast material to be delivered based on the patient's weight. For example, if the patient weighs less than 180 pounds (<82 kg), 100 ml of IV contrast material is given; 180-250 pounds (82-114 kg), 150 ml of IV contrast material is given; and more than 250 pounds (>114 kg), 150-200 ml of IV contrast material is given. For statistical purposes in this study, we assumed the average patient weighs less than 180 pounds (81 kg) and that therefore the institution routinely uses 100 ml of IV contrast material.
The results of our survey are summarized in Tables1,2,3. In the rows "Collimation," "Reconstruction," "Volume," "Rate," and "Scan delay," the mean value is reported first, followed by the range of values reported. Most institutions reported using a thinner collimation for the abdomen and a thicker collimation for the pelvis. However, the average collimation used in the abdomen and the average collimation used in the pelvis differ by less than 1 mm for each protocol. Therefore, for simplicity, the values reported for "Collimation" represent the collimation used for the abdomen unless otherwise stated.
Some respondents indicated that contrast material (oral, rectal, or IV) is administered only in certain patients or "as needed" (i.e., selective). This is reflected in the table rows entitled "Routine," indicating the routine administration of contrast material, and "Selective," indicating the selective use of contrast material.
To condense the results and discussion, protocols for staging breast, colon, prostate, and other cancer and lymphoma are grouped together under the heading of "Cancer Staging Protocols" in Table 1. Evaluation of a renal or adrenal mass is dealt with under the heading of "Renal and Adrenal Mass Protocols" in Table 2, and the protocols for abdominal pain, renal colic, rule out abscess, rule out diverticulitis, and rule out appendicitis are dealt with under "Abdominal Pain Protocols" in Table 3.
IV contrast material is routinely administered by only 22% of responding institutions for evaluating adrenal mass and 4% for renal colic. Because IV contrast material is not routinely used for these protocols by most institutions, the volume, rate, and scan delay for these protocols are not reported. When asked about the scan delay used after the administration of IV contrast material, some respondents merely indicated "arterial phase" or "portal venous phase"; thus, specific values are not reported for "Scan delay" in Table 1 ("Breast Cancer") or Table 2 ("Renal Mass").
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The results of the survey indicate a wide range in the number of protocols used for helical CT of the abdomen and pelvis. There is no correlation between the number of protocols used and the number of scanners at each institution (p = 0.77). One possible explanation for the wide range in the number of protocols is the fact that the survey population is a select group of academic institutions that likely perform CT for a large number of patients and for a wide range of indications. In the institutions with more protocols, an effort may have been made to design protocols to address specific clinical questions common to their institutional practice.
CT scans are not routinely reviewed before the patient leaves the CT suite at 39% of the institutions. The advantage of this approach is improved throughput of patients, whereas the possible disadvantage is that patients may need to return for additional imaging because of suboptimal technique or to clarify a finding seen on routine scans. One might assume that institutions that do not routinely check scans before the patient leaves the department use more IV contrast material, whereas those checking examinations might routinely check unenhanced scans before determining whether to administer IV contrast material. However, there is no significant difference between the use of IV contrast material at institutions that do and those that do not routinely check examinations before the patient leaves the department (86% versus 83%, respectively; p = 0.46).
IV Contrast Material
In the survey conducted in 1993 of CT of the liver, 46% of the institutions
used nonionic IV contrast material for 76-100% of patients
[6], and in the survey
conducted in 1996, 39% of the institutions used low-osmolar contrast material
in more than 75% of patients
[7]. In our survey, when IV
contrast material is administered, 46% of institutions use nonionic contrast
material (which we are equating with low-osmolar contrast material) in more
than 75% of patients. The recent increase in the use of nonionic contrast
material may be because its cost is approaching that of ionic contrast
material or may reflect higher injection rates or increased concern about
contrast reactions. In our survey, there is no significant correlation
(p = 0.87) between the frequency of nonionic contrast material use
and the frequency of administration of IV contrast material.
Nonionic IV contrast material was used exclusively by 38%, 26% and 39% of institutions in the 1993, 1996, and current surveys, respectively [6, 7]. The exclusive use of nonionic contrast material may offer several advantages with respect to efficiency and the use of resources devoted to monitoring and treating contrast reactions. The fluctuations over time may also be related to changes in the cost of nonionic contrast material.
IV contrast material is used most commonly for cancer staging protocols and least commonly for renal colic (1/28 [4%]). When IV contrast material is prescribed, the average volume injected is 141 ml at a rate of 3 ml/sec. In 1993, most institutions used an injection rate of 1.5-2.0 ml/sec; in 1996, most used a rate of 2.5-3.0 ml/sec. The trend toward faster injection rates may be associated with access to faster scanners and a greater comfort among radiologists with using faster injection rates [8].
Collimation and Reconstruction Interval
The average collimation is 7 mm for all protocols except protocols for
renal colic (5 mm), evaluation of renal mass (5 mm), and evaluation of adrenal
mass (4 mm). One of the advantages of helical CT is that images can be
retrospectively reconstructed at thinner intervals than the prescribed
collimation and most institutions (86%) use a reconstruction interval that is
equal to or less than the collimation. However, 14% (4/28) of the institutions
routinely use a reconstruction interval that is greater than the
collimation.
Cancer Staging Protocols
Oral and IV contrast material are used by 100% of the responding
institutions for staging cancer of the breast, colon, and prostate; for
staging "other cancer"; and for staging lymphoma except for one
institution that does not routinely use IV contrast material for lymphoma
staging. This finding probably reflects the general consensus that the use of
IV contrast material is essential for detection of liver metastases and that
oral contrast material may be useful in differentiating an unopacified loop of
bowel from a soft-tissue mass or retroperitoneal lymph node. For cancer
staging protocols, rectal contrast material is routinely given most frequently
for colon cancer staging (39% of the institutions) and least frequently for
breast cancer staging (7%). One institution (4%) routinely referred patients
for prostate cancer staging to MR imaging rather than CT.
Multiphasic liver scanning is reported to be more sensitive than uniphasic scanning for the detection of so-called hypervascular liver metastases because some of these liver metastases may be better appreciated on either unenhanced or arterial phase images [9,10,11]. Although there is some controversy in the literature, breast cancer is usually categorized as a primary tumor that can produce hypervascular liver metastases [10, 12]. The controversy is reflected in the results of our survey. In addition to portal venous phase scans of the liver, which 100% of the institutions obtain, 21% of the institutions obtain unenhanced scans, and 39% of the institutions obtain arterial phase scans. Fifty percent of the institutions obtain scans during the portal venous phase only and 50% of the institutions obtain scans using two or three phases. It is possible that institutions that use multiphasic liver scanning may have a larger population of patients with breast cancer, but this correlation was not studied in our survey.
The average collimation and reconstruction interval used for cancer staging in the abdomen is 7 mm. This finding is consistent with the results of prior surveys that have shown a trend over time toward scanning the liver with thinner collimation [7].
Renal and Adrenal Mass Protocols
Although 100% of institutions administer IV contrast material for
evaluating a renal mass, only 82% of institutions indicated that a preliminary
unenhanced scan is routinely obtained. Unenhanced renal images are considered
extremely important for renal lesion characterization
[13,14,15],
permitting evaluation of renal calcifications and measurement of lesion
enhancement.
There was no consensus on how to protocol evaluate adrenal mass. For this hypothetical protocol, 30% of the institutions routinely obtain unenhanced scans only, 22% routinely obtain contrast-enhanced scans only, 33% routinely obtain both unenhanced and contrast-enhanced scans, and 15% give IV contrast material on a selective basis. One institution routinely refers these patients to MR imaging. Another institution commented that a specific protocol exists for the evaluation of an adrenal mass that includes a plan in the event of a hypertensive crisis.
Abdominal Pain Protocols
Helical CT has been shown to be more accurate and less time-consuming than
excretory urography in examining patients with renal colic
[16,
17]. Because virtually all
urinary tract calculi can be seen on unenhanced scans, one of the advantages
of using CT instead of excretory urography is that neither IV contrast
material nor oral contrast material is necessary to depict urinary tract
calculi and the changes of urinary tract obstruction. For renal colic, 75% of
the institutions do not routinely give IV contrast material and only one
institution (4%) routinely administers IV contrast material.
In our survey, the use of IV, oral, and rectal contrast material is similar for protocols for abdominal pain, to rule out abscess, and to rule out diverticulitis. For these hypothetical requisitions, IV and oral contrast material are almost always administered, whereas rectal contrast is routinely administered at a minority of institutions.
Several studies have documented a high accuracy for CT in the diagnosis of appendicitis using a variety of techniques [18,19,20]. These studies were performed with oral and IV contrast material [18], without IV or enteric contrast material [19], and with rectal contrast material only [20]. In our survey, to rule out appendicitis, IV, oral, and rectal contrast material are routinely given by 79%, 82%, and 32% of institutions, respectively. IV contrast material to rule out appendicitis is used somewhat less than for indications such as abdominal pain and rule out abscess; this finding may reflect the targeted nature of the examination and the fairly specific clinical presentation associated with this condition. Twenty-one percent of the institutions routinely use IV, oral, and rectal contrast material simultaneously. The variation among institutions is consistent with the range of techniques that have been proposed in the literature for CT evaluation of appendicitis.
There are limitations to our study. Although our institutional response rate was high (78%), the results do not represent all possible institutions and only reflect data from certain academic institutions in the United States. The responses to the survey were completed without using a method to verify all of them. However, if a given survey was returned and responses were unclear or inconsistent, the respondent was contacted to clarify the responses. Our survey did not take into consideration the fact that scanning parameters may be influenced by factors that are manufacturer-specific. Nevertheless, the basic principles of helical CT technology apply to all manufacturers and most currently available scanners have roughly similar scanning capabilities.
In summary, our survey results show a wide range in the number of protocols used for helical CT of the abdomen and pelvis. IV contrast material is routinely administered for 90% (median) of studies. When IV contrast material is administered, nonionic IV contrast material is used 68% (median) of the time. With the exception of evaluate adrenal mass, whenever there is a requisition for cancer staging or for evaluation of a mass, IV contrast material is almost always prescribed. When IV contrast material is administered, approximately 140 ml is given at an average rate of 3 ml/sec. Rectal contrast material is used most commonly for colon cancer staging but is used by a minority of institutions. Scans are typically obtained with a 7-mm collimation and a reconstruction interval of 7 mm. A thinner collimation is used when scanning the kidneys (mean, 5 mm) and adrenal glands (mean, 4 mm).
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1.5 cm) malignant hepatic neoplasms.
AJR
1995;164:879
-8843 cm)
hyperechoic renal masses: comparison of helical and conventional CT for
diagnosing angiomyolipoma. AJR
1996;167:877
-8813.0 cm) renal parenchymal tumor:
detection, diagnosis, and controversies. Radiology
1991;179:307
-317
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