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Commentary
Dynamic Hepatic CT Scanning
W. Dennis Foley1
Contrast-enhanced hepatic CT scan techniques used to enhancement reflecting renal filtration. Contrast material dif-
evaluate suspected metastatic disease vary widely, largely fuses into the interstitial spaces of tumors during all three
because of a lack of consensus on contrast load, scanning phases. With bolus contrast delivery, tumor enhancement
sequence, and factors affecting lesion detectability. occurs during the relatively short time of contrast delivery and
In contrast-enhanced studies, the rate and amount of con- nonequilibrium or redistribution. With bolus contrast, there is
trast material delivered to normal hepatic parenchyma and to less time for tumor enhancement to occur during the relatively
focal tumors should depend on local blood supply and the short contrast delivery and nonequilbrium or redistribution
degree of cellularity, fibrosis, and necrosis in each region. phases than with the sustained nonequilbrium phase induced
Normal hepatic parenchyma is best enhanced by rapid and by an infusion. As Paushter et al. point out, in the preceding
sustained delivery of a large contrast bolus (45-50 g iodine article [3], persistent “nonequilibrium” achieved by infusion
administered over 2_21/2 mm), not by an infusion technique techniques does not guarantee lesion detectability equivalent
(42 g iodine delivered over 5-1 0 mm). Most hepatic metas- to that achieved with bolus contrast delivery.
tases are hypovascular in relation to hepatic parenchyma and In order to obtain complete hepatic CT coverage via bolus
have areas of fibrosis and necrosis into which contrast media contrast delivery, an incremental dynamic scan technique with
diffuse at relatively slow rates. Better liver-to-lesion contrast short scan times, short interscan delays, and technical factors
is achieved with bolus than infusion techniques because to optimize image quality is necessary. The combination of
parenchyma is more enhanced and less contrast medium bolus contrast delivery and incremental dynamic scan should
diffuses into the interstitial spaces of tumors. ensure greater lesion detectability than an infusion technique.
In order to understand the pharmacokinetics of contrast This working hypothesis, which has been assumed correct
material delivery and diffusion following sustained bolus injec- for several years, has been tested by Paushter et al. [3]. Their
tion (42-50 g iodine over 2_2h/2 mm), three distinct phases comparison of noncontrast, bolus dynamic, and bolus-plus-
can be considered [1, 2]. During the bolus phase, there is drip-infusion nondynamic techniques confirms the superiority
marked vascular and parenchymal enhancement, which Of the bolus dynamic approach in terms of the number of
peaks at the end of injection. This is followed by a short lesions detected, delineation of lesion margins, determination
“nonequilibrium phase” in which vascular enhancement de- of lesion size, and overall conspicuity. Significantly, Paushter
clines relatively rapidly before equilibrating with parenchymal et al. found that noncontrast scanning resulted in slightly
enhancement. The rapid drop in vascular enhancement re- more detected lesions than the loading bolus-plus-drip-infu-
sults from continuing intravascular to extravascular contrast sion technique and that some lesions were smaller on the
redistribution in liver parenchyma. The third, or equilibrium, loading bolus-plus-drip-infusion technique than on the non-
phase is one of gradually declining vascular and parenchymal contrast study. Thus, the loading bolus-plus-drip-infusion
This articleis a commentary on the preceding article by Paushter et al.
‘Department of Radiology, Medical College of Wisconsin, 8700 W. Wisconsin Ave., Milwaukee, WI 53226. Address reprint requests to W. D. Foley.
AJA 152:272-274, February 1989 0361 -803X/89/1 522-0272 C American Roentgen Ray Society
AJA:152, February 1989 DYNAMIC HEPATIC CT SCANNING 273
technique was even less efficacious than a noncontrast scan. injected over 140 sec (5 mI/sec for 10 sec and 1 mI/sec for
Obviously, contrast-enhancement techniques should be used 1 30 sec). For routine hepatic CT scanning, Paushter et aI.
to improve, not diminish, lesion detectability. advocate 1 00-1 50 ml of contrast material injected at 1 ml/
The incremental dynamic hepatic CT scan with bolus con- sec. Many years of angiographic experience has shown
trast delivery should be used in a broad range of patients with clearly that 3 mI/kg/hr is a tolerable load of contrast material
suspected hepatic metastasis, which is most common in when given to patients with normal renal function. In our
patients with primary malignancies involving the colon, lung, practice, the formula is adjusted to 3 mI/kg in 2 mm. Rate of
breast, pancreas, or endometrium and in those with mela- delivery has no deleterious effect on renal function, as we
noma or sarcomas. Tumors that may be hypervascular in have demonstrated with serial postprocedure determinations
relation to normal hepatic parenchyma (e.g., primary hepa- of serum creatinine at 24, 48, and 72 hr and 7 days after the
toma and metastases from pancreatic islet cell tumor, carci- procedure [2]. In addition, patients with normal cardiac func-
noid, and renal carcinoma) may be isodense during an incre- tion can tolerate an acute intravascular volume expansion of
mental dynamic hepatic CT scan obtained during bolus con- 1 I. One hundred eighty milliliters of 60% ionic contrast
trast administration [4]. material is equivalent to approximately 750 ml of normal
Paushter et al. describe their dynamic CT scan as being saline. In our practice, only a few patients with cardiac decom-
acquired during the “early bolus phase” and state that hyper- pensation have required evaluation for suspected hepatic
vascular lesions are less likely to be isodense with their metastases. Evaluation of these patients should be tailored
approach than with dynamic techniques in which the onset of to each individual by using noncontrast CT and other alter-
scanning is delayed for 45 sec rather than 1 5 sec after the native imaging techniques including sonography and isotope
beginning of bolus injection. However, a 45-sec scan delay scans.
has two purposes. First, hepatic parenchymal enhancement A volume flow rate injector that can be operated by a
is greater at 45 sec than 1 5 sec and reaches a relative plateau technologist from the CT scan console is an integral compo-
at that time. Second, hepatic veins are positively enhanced nent of an incremental dynamic bolus contrast-enhanced
at 45 sec and not at 15 sec, allowing detected lesions in the hepatic CT study. Contrast given by hand injection is not as
cephalad portion of the liver to be localized to specific lobes accurate in its timing, not as reproducible, and not as conven-
and segments. In the timing sequence used by Paushter et ient. With volume flow rate injectors, contrast material is
al. [3], most of the hepatic scans are obtained after the end delivered through standard angiographic catheters (1 9 or 20
of injection, during the phase of intravascular to extravascular gauge) either 1 1/4 in. (3.2 cm) or 2 in. (5.1 cm) in length
contrast redistribution before contrast equilibrium is obtained. preferably into antecubital veins, at rates that vary between
In essence, they used a smaller bolus and earlier dynamic 5 mI/sec (initial 1 0 sec) and 1 mI/sec (subsequent 130 sec).
scan than Bressler et al. [4] or Alpern et al. [5], but they still A volume flow rate injector ensures consistent contrast deliv-
obtained scans both during contrast material delivery and in ery, an important feature in patients having sequential CT
the early nonequilibrium phase. The consensus, as Paushter scans to assess tumor response to chemotherapy or radiation
et al. state, is that patients with suspected hypervascular therapy.
tumors should have both a noncontrast and a dynamic post- Given the convenient feature of a volume flow rate injector
contrast study. The dynamic postcontrast study still may operated by the CT technologist, the radiologist can supervise
detect hypervascular metastases or other multifocal sites of to ensure that the examination is tailored to the particular
hepatoma not apparent on the precontrast examination. patient’s circumstances. For example, a patient with sus-
A number of practical issues affect the choice of hepatic pected recurrent carcinoma of the rectum would best be
CT scan technique in individual practices. The CT scanner evaluated with an abdomen/pelvis CT technique in which the
should be capable of rapid repetitive scanning at contiguous initial component of the study is a dynamic hepatic sequence.
levels with scan techniques that can detect low-contrast A patient undergoing staging CT for carcinoma of the lung
lesions equal in diameter to the slice thickness used. The could be evaluated with an abdomen/thorax CT study in
scan repetition rate should be between 7 and 1 0 contiguous which the initial scan sequence is a dynamic hepatic CT,
scans per minute so that the liver can be evaluated over 1 V2- programmed in a caudal to cephalic sequence from the tip of
21/2 mm, depending on hepatic size. Relatively rapid incre- the right hepatic lobe to the dome of the right hemidiaphragm.
mental dynamic scanning requires the cooperation of the The radiologist or a designated assistant, such as a second
patient for controlled breathing between individual scans or technologist or nurse, must palpate the injection site to ensure
between sequences of scans obtained during one breath- that the contrast material delivered through the plastic venous
hold. This prevents slice misregistration due to unequal res- cannula does not extravasate. If extravasation occurs, the
piration, which can result in lesions being missed because of injection should be stopped immediately.
overlapping slices and missing segments in scans that are The optimal method for delivering IV contrast through an-
contiguous in space but not contiguous anatomically. tecubital veins is to position the patient’s arm at a right angle
If the radiologist has access to suitable CT equipment and to the chest by placing the palm of the hand against the face
a cooperative patient, the second issue affecting the use of of the CT gantry. This ensures that injected contrast material
dynamic scanning with bolus contrast delivery is the amount is not constricted at the thoracic outlet.
of contrast material used. In our practice, we administer 50 g If the four factors discussed above (CT scanner perform-
of iodine load to patients with normal cardiorenal function. ance, a proper understanding of contrast material tolerance
One hundred eighty milliliters of 60% contrast material is and toxicity, availability of a volume flow rate injector, and
274 FOLEY AJR:152, February 1989
adequate supervision of the injection site) are all available and 2. Foley WD, Beriand LL, Lawson TL, Smith DF, Thorsen MK. Contrast-
enhancement technique for dynamic hepatic CT scanning. Radiology
attended to properly, dynamic hepatic CT scanning can be
1983;147:797-803
implemented on a routine basis. This approach will improve 3. Paushter DM, Zeman AK, Scheibler ML, Choyke PL, Jaffe MH, Clark
lesion detectability on enhanced hepatic CT scans. LA. CT evaluation of suspected hepatic metastases: comparison of
techniques for IV contrast enhancement. AJR 1989;1 52:267-271
4. Bressler EL, Alpern MB, Glazer GM, et al. Hypervascular hepatic metas-
REFERENCES
tases: CT evaluation. Radiology 1987;1 62:49-51
1. Burgener FA, Hamlin DJ. Contrast-enhancement of hepatic tumors in CT: 5. Alpem MB, Lawson TL, Foley WD, et al. Efficiency of contrast-enhanced
comparison between bolus and infusion techniques. AJR 1983;140: incremental dynamic computed tomography in the detection of focal
291-295 hepatic masses and fatty infiltration. Radiology 1986;1 58:45-50
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