Radiology
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Published online before print October 2, 2007, 10.1148/radiol.2451061585
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
2451061585v1
245/3/779    most recent
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Chu, L. L.
Right arrow Articles by Yeh, B. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Chu, L. L.
Right arrow Articles by Yeh, B. M.
(Radiology 2007;245:779-787.)
© RSNA, 2007

Gastrointestinal Imaging

Patient-specific Time to Peak Abdominal Organ Enhancement Varies with Time to Peak Aortic Enhancement at MR Imaging1

Lisa L. Chu, BA, Bonnie N. Joe, MD, PhD, Antonio C. A. Westphalen, MD, Emily M. Webb, MD, Fergus V. Coakley, MD, and Benjamin M. Yeh, MD

1 From the Department of Radiology, University of California-San Francisco, 505 Parnassus Ave, Box 0628, C-324C, San Francisco, CA 94143-0628. Received September 13, 2006; revision requested November 11; revision received January 5, 2007; final version accepted February 5. B.M.Y. received the ARRS/Philips Medical Systems Scholarship. Address correspondence to B.M.Y. (e-mail: ben.yeh{at}radiology.ucsf.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
Purpose: To retrospectively evaluate the relationship between the times to peak enhancement of the liver, pancreas, and jejunum with respect to the time to peak aortic enhancement at magnetic resonance (MR) imaging.

Materials and Methods: The committee on human research approved this study and waived written informed consent. This study was HIPAA compliant. The study retrospectively identified 141 patients (63 men, 78 women; mean age, 57 years) who underwent abdominal MR imaging by using a test bolus that was monitored approximately every second for 2 minutes with a spoiled gradient-echo T1 transverse section through the upper abdomen. The times to peak enhancement of the aorta, liver, pancreas, and jejunum were recorded and correlated with the time to peak aortic enhancement, age, and sex by means of univariate and multivariate linear regression analyses.

Results: The mean time to peak aortic enhancement was 21.1 seconds (range, 8.7–41.8 seconds). The times to peak enhancement of the liver, pancreas, and jejunum were positively and linearly correlated with the time to peak aortic enhancement (r = 0.69, 0.86, and 0.80, respectively, all P < .001) and were 3.39, 1.64, and 2.04 times longer than the time to peak aortic enhancement, respectively. Age, sex, and history of heart disease did not give additional predictive information for determining the time to peak visceral enhancement.

Conclusion: The times to peak enhancement of the liver, pancreas, and jejunum are linearly related to that of the aorta. These results could potentially allow tailored patient- and organ-specific scan delay optimization at contrast material–enhanced MR image evaluation.

© RSNA, 2007


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
Intravenous contrast material is commonly given to improve the diagnostic yield of both computed tomography (CT) and magnetic resonance (MR) imaging of the abdomen. It is well known that the choice of scan delay time influences the conspicuity of lesions in the liver (1–10) and pancreas (11–14). For certain cancers, such as primary or metastatic adenocarcinoma, it is thought that peak organ enhancement will provide the maximum contrast between normal enhancing tissue and less enhancing hypovascular tumors (11–14).

A problem with determining delays for MR and CT imaging is that blood circulation times may vary dramatically between individuals. For example, the time and magnitude of peak aortic enhancement vary with left ventricular ejection fraction, coronary artery disease, age, and weight (15–18). For these reasons, fixed scan delays may result in imaging when enhancement of abdominal organ parenchyma is not ideal and may decrease the conspicuity of hypovascular cancers. To account for interpatient variability in blood circulation times, timing bolus and bolus-triggered techniques have been introduced to optimize arterial scan delays for MR angiography (19–24), CT angiography (25,26), and the arterial phase of hepatic MR (9,10,27–29) and CT imaging (4,30–32). However, these methods do not address optimization of parenchymal enhancement for the liver, pancreas, and bowel. Optimization of bowel wall enhancement is becoming of interest as increased focus is directed toward MR and CT enterography.

Determination of patient-specific scan delays for these abdominal organs depends on understanding the relationship between time to peak aortic enhancement and the time to peak abdominal organ enhancement, but this relationship has not been previously described by using high temporal resolution. Thus, the purpose of our study was to retrospectively evaluate the relationship between the times to peak enhancement of the liver, pancreas, and jejunum with respect to the time to peak aortic enhancement at MR imaging.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
Patients
Our retrospective single-institution study was approved by the Committee on Human Research at the University of California-San Francisco (San Francisco, Calif). This study was compliant with the Health Insurance Portability and Accountability Act, and written informed consent was waived. An electronic database search was performed to identify all patients who underwent timing bolus transverse imaging of the midabdominal aorta as part of their routine abdominal MR imaging study between June 2004 and June 2006. In June 2004, we introduced a test bolus injection for calculation of patient-specific arterial imaging delays as part of our routine abdominal MR imaging protocol.

One-hundred forty-one patients were identified, of which 78 were women (age range, 12–92; mean age, 56 years) and 63 were men (age range, 15–95; mean age, 58). The primary indications for imaging included suspected renal artery stenosis (n = 38), evaluation of liver lesions (n = 27), screening for possible hepatocellular carcinoma (n = 18), abdominal pain (n = 17), suspected other malignancy (n = 13), metastases (n = 7), suspected or known pancreatitis (n = 6), venous thrombosis (n = 5), kidney lesions (n = 4), suspected biliary disease (n = 4), and abdominal mass (n = 2). To determine the presence of clinical disease of the liver, pancreas, jejunum, and heart, one author (L.L.C.) reviewed all available medical records and, for each patient, recorded the history of cirrhosis, noncirrhotic chronic liver disease, pancreatitis, pancreatic cancer, jejunal disease (eg, Crohn disease, ulcerative jejunitis, neoplasms), and cardiac disease (eg, coronary artery disease, valvular heart disease, myocardial infarction, congestive heart failure).

MR Technique
All patients underwent MR imaging with a phased-array coil performed with a 1.5-T scanner. Of the 141 patients, 114 patients were examined by using a 1.5-T imager (Gyroscan Intera; Philips, Best, the Netherlands), and 27 patients were imaged by using a 1.5-T imager (Magnetom Vision; Siemens Medical Solutions, Erlangen, Germany).

A timing examination was performed by using a test bolus injection of 2 mL of gadodiamide (Omnipaque; GE Healthcare, Madison, Wis) followed by injection of 10 mL of normal saline into an antecubital vein at a rate of 2 mL/sec with an MR-compatible power injector (Spectris; Medrad, Pittsburgh, Pa). The volumes of the power injector tubing and angiocatheter were 3 mL and less than 1 mL, respectively. All patients were instructed to breathe quietly during the examination. A transverse T1 spoiled gradient-echo image (Philips 1.5-T: repetition time msec/echo time msec 14.75/1.47; flip angle, 60°; field of view, 30–40 cm; section thickness, 10 mm; matrix, 256 x 96; and Siemens 1.5-T: 4.5/2.2; flip angle, 8°, field of view, 30–38 cm; section thickness, 10 mm; matrix, 128 x 96), centered on the midabdominal aorta, was repeated approximately every second from the start of injection for up to 2 minutes. The intervals between images were recorded and varied depending on the field of view that was used and ranged from 0.90 to 1.20 seconds per image.

Data Analysis
The images were transferred to a desktop computer (Dimension 4700; Dell, Round Rock, Tex) for data analysis by using a commercially available image analysis software program (MIStar; Apollo Medical Imaging, Melbourne, Australia). Two authors (B.M.Y., an attending radiologist with 6 years experience in abdominal MR imaging, and L.L.C., a trainee) reviewed all MR images by consensus, and circular or polygonal regions of interest (ROIs) were manually drawn over the aorta, pancreas, jejunum, and liver.

Regions of interest encompassed at least 20 voxels and were drawn to avoid any visible blood vessels, ducts, cysts, or prominent artifacts. Because of respiratory motion and peristalsis, the ROIs for the pancreas and jejunum occasionally required manual adjustment for each section. The ROIs of the organs of interest could not be obtained in some patients due to excessive respiratory movement, variable section selection, and motion artifact. Signal intensity–time curves were then automatically generated by using the image analysis software. The time to peak enhancement was determined to be the maximum signal intensity of each curve and was tabulated for each patient.

Statistical Analysis
Statistical analysis was performed by using a software program (Stata, version 8.0; Stata, College Station, Tex). Univariate linear regression analysis was performed by using a weighted least-squares approach to describe the relationship between the time to peak aortic enhancement and the times to peak enhancement of the liver, pancreas, and jejunum. To adjust for the heterogeneous variance, which was roughly proportional to time to peak enhancement, we used a weighted form of least-squares where the least-squares weights were modeled as inversely proportional to the square of the time to peak enhancement (33).

A Pearson correlation (r) was calculated to determine the degree of linear correlation between the times to peak enhancement of the aorta and each of the organs of interest, and the strength of the correlations were compared. Analysis of variance was performed to assess for any significant differences in the times to peak enhancement among patients without known liver disease, with noncirrhotic liver disease, and with cirrhosis. Multivariate linear regression models were also used to assess whether patient age, sex, or presence of cardiac disease provided predictive information beyond that given by the time to peak aortic enhancement for determination of the times to peak enhancement of the liver, pancreas, and jejunum, respectively. For all tests, a P value of less than .05 was considered to indicate a significant difference.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
Patients and Measurements
In 134 patients, hepatic time to peak enhancement could be measured (Table) from the T1-weighted MR images of the abdomen (Fig 1) by its corresponding graph of signal intensity versus time for the ROI (Fig 2). Ninety-one of these patients did not have liver disease, 30 patients had noncirrhotic liver disease, and 13 had cirrhosis as per the available medical records. The noncirrhotic liver disease resulted from liver metastases (n = 7), hepatitis C (n = 5), hepatitis B (n = 5), steatosis (n = 5), primary sclerosing cholangitis (n = 2), liver transplantation with prior history of cirrhosis (n = 2), hepatocellular carcinoma (n = 1), congestive hepatopathy (n = 1), nodular regenerative hyperplasia (n = 1), and hemochromatosis (n = 1). For the 13 patients with cirrhosis, the cause was attributed to hepatitis C (n = 4), alcohol (n = 2), primary biliary cirrhosis (n = 2), hepatitis B (n = 1), hepatitis C and alcohol (n = 1), primary biliary atresia (n = 1), and unknown cause (n = 2).


View this table:
[in this window]
[in a new window]

  		Patients Studied for Time to Peak Enhancement

 

Figure 1A
View larger version (125K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1a: Transverse dynamic gadolinium-enhanced MR images (4.5/2.2; flip angle, 8°; field of view, 30–38 cm; section thickness, 10 mm; matrix, 128 x 96) of 58-year-old woman show ROIs drawn on the aorta (A), liver (L), pancreas (P), and jejunum (J). Images obtained at (a) 3.0 seconds prior to contrast material arrival in the abdomen and (b) 16.8 seconds (time of peak aortic enhancement), (c) 22.4 seconds (time of peak pancreatic enhancement), (d) 24.3 seconds (time of peak jejunal enhancement), and (e) 51.3 seconds (time of peak hepatic enhancement) after contrast material injection.

 

Figure 1B
View larger version (128K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1b: Transverse dynamic gadolinium-enhanced MR images (4.5/2.2; flip angle, 8°; field of view, 30–38 cm; section thickness, 10 mm; matrix, 128 x 96) of 58-year-old woman show ROIs drawn on the aorta (A), liver (L), pancreas (P), and jejunum (J). Images obtained at (a) 3.0 seconds prior to contrast material arrival in the abdomen and (b) 16.8 seconds (time of peak aortic enhancement), (c) 22.4 seconds (time of peak pancreatic enhancement), (d) 24.3 seconds (time of peak jejunal enhancement), and (e) 51.3 seconds (time of peak hepatic enhancement) after contrast material injection.

 

Figure 1C
View larger version (129K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1c: Transverse dynamic gadolinium-enhanced MR images (4.5/2.2; flip angle, 8°; field of view, 30–38 cm; section thickness, 10 mm; matrix, 128 x 96) of 58-year-old woman show ROIs drawn on the aorta (A), liver (L), pancreas (P), and jejunum (J). Images obtained at (a) 3.0 seconds prior to contrast material arrival in the abdomen and (b) 16.8 seconds (time of peak aortic enhancement), (c) 22.4 seconds (time of peak pancreatic enhancement), (d) 24.3 seconds (time of peak jejunal enhancement), and (e) 51.3 seconds (time of peak hepatic enhancement) after contrast material injection.

 

Figure 1D
View larger version (130K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1d: Transverse dynamic gadolinium-enhanced MR images (4.5/2.2; flip angle, 8°; field of view, 30–38 cm; section thickness, 10 mm; matrix, 128 x 96) of 58-year-old woman show ROIs drawn on the aorta (A), liver (L), pancreas (P), and jejunum (J). Images obtained at (a) 3.0 seconds prior to contrast material arrival in the abdomen and (b) 16.8 seconds (time of peak aortic enhancement), (c) 22.4 seconds (time of peak pancreatic enhancement), (d) 24.3 seconds (time of peak jejunal enhancement), and (e) 51.3 seconds (time of peak hepatic enhancement) after contrast material injection.

 

Figure 1E
View larger version (132K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1e: Transverse dynamic gadolinium-enhanced MR images (4.5/2.2; flip angle, 8°; field of view, 30–38 cm; section thickness, 10 mm; matrix, 128 x 96) of 58-year-old woman show ROIs drawn on the aorta (A), liver (L), pancreas (P), and jejunum (J). Images obtained at (a) 3.0 seconds prior to contrast material arrival in the abdomen and (b) 16.8 seconds (time of peak aortic enhancement), (c) 22.4 seconds (time of peak pancreatic enhancement), (d) 24.3 seconds (time of peak jejunal enhancement), and (e) 51.3 seconds (time of peak hepatic enhancement) after contrast material injection.

 

Figure 2
View larger version (13K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 2: Graph of signal intensity versus time shows times to peak enhancement for the aorta (16.8 seconds), pancreas (22.4 seconds), jejunum (24.3 seconds), and liver (51.3 seconds) for patient in Figure 1.

 
Time to peak pancreatic enhancement could be measured in 102 patients. Of these, 96 did not have pancreatic disease, five had pancreatitis (three chronic, one acute, and one unspecified), and one had lung metastases to the pancreas. Time to peak jejunal enhancement could be measured in 66 patients, none of whom had a record of bowel disease in the available medical records. Eighteen patients had a history of cardiac disease.

Individual Time to Peak Organ Enhancement
The distribution of times to peak enhancement of the aorta, liver, pancreas, and jejunum showed wide interpatient variation (Figs 3 and 4). The mean time to peak aortic enhancement was 21.1 seconds (standard deviation, 6.5 seconds; range, 8.7–41.8 seconds). By using univariate linear regression, the time to peak aortic enhancement was significantly and positively correlated with increasing age (P = .001), male sex (P = .003), and presence of heart disease (P < .001).


Figure 3
View larger version (16K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 3: Box plots of times to peak enhancement for the aorta, liver, pancreas, and jejunum. The time to peak enhancement varies widely for each structure. The horizontal line through each box represents mean time to peak enhancement. The top and bottom of each box represent interquartile range (75% and 25%), and the whiskers mark the 5% and 95% range. No significant difference was found in mean times to peak hepatic enhancement for patients without record of liver disease, noncirrhotic disease, or cirrhosis (P = .43, analysis of variance).

 

Figure 4
View larger version (24K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 4: Graph shows times to peak enhancement for representative sample of patients. Each curve represents one patient's times to peak enhancement of the aorta, pancreas, jejunum, and liver. Wide interpatient variability is seen in times to peak enhancement for each structure. As the time to peak aortic enhancement increases, the corresponding times to peak enhancement of the pancreas, jejunum, and liver increase. Note that ordering of organs from left to right was chosen on the basis of increasing mean times to peak enhancement.

 
Similarly, the mean times ± standard deviation to peak hepatic, pancreatic, and jejunal enhancement were 56.6 seconds ± 16.5 (range, 26.5–119 seconds), 31.7 seconds ± 10.3 (range, 14.4–68.4 seconds), and 36.5 seconds ± 13.8 (range, 15.5–91.2 seconds), respectively. There was no significant difference in the mean times to peak enhancement (Fig 3) among patients without known liver disease (55.7 seconds), with noncirrhotic liver disease (57.1 seconds), and with cirrhosis (62.0 seconds; P = .43, analysis of variance). The mean times ± standard deviation to peak pancreatic enhancement for patients with or without pancreatitis were 31.5 seconds ± 10.2 and 38.2 seconds ± 9.8, respectively.

Correlation and Regression Analysis
Scatterplots of the aorta versus the liver, pancreas, and jejunum (Fig 5) revealed a positive linear correlation between times to peak aortic enhancement and times to peak enhancement of the liver, pancreas, and jejunum. In univariate linear regression analysis, the times to peak enhancement of the liver, pancreas, and jejunum were all positively and linearly correlated with that of the aorta (r = 0.69, 0.86, and 0.80, respectively, all P < .001), and the relationships could be described by using the following equations: TTPL = 3.39·TTPA – 15.0 seconds, TTPP = 1.64·TTPA – 3.42 seconds, and TTPJ = 2.04·TTPA – 7.44 seconds, where TTPA, TTPL, TTPP, and TTPJ refer to the time to peak enhancement of the aorta, liver, pancreas, and jejunum, respectively. The correlation between the time to peak aortic and hepatic enhancement (r = 0.69) was significantly lower than that of aortic enhancement and either pancreatic (r = 0.86, P < .005) or jejunal (r = 0.80, P < .05) enhancement.


Figure 5A
View larger version (11K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 5a: Graphs show time to peak aortic enhancement relative to those of the (a) liver, (b) pancreas, and (c) jejunum. The time to peak aortic enhancement was linearly correlated to times to peak enhancement of the liver, pancreas, and jejunum (r = 0.69, 0.86, and 0.80, respectively, all P < .001). The correlation between the times to peak aortic and hepatic enhancement was not as strong as that between peak aortic and either peak pancreatic (P < .05) or jejunal (P < .001) enhancement.

 

Figure 5B
View larger version (9K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 5b: Graphs show time to peak aortic enhancement relative to those of the (a) liver, (b) pancreas, and (c) jejunum. The time to peak aortic enhancement was linearly correlated to times to peak enhancement of the liver, pancreas, and jejunum (r = 0.69, 0.86, and 0.80, respectively, all P < .001). The correlation between the times to peak aortic and hepatic enhancement was not as strong as that between peak aortic and either peak pancreatic (P < .05) or jejunal (P < .001) enhancement.

 

Figure 5C
View larger version (9K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 5c: Graphs show time to peak aortic enhancement relative to those of the (a) liver, (b) pancreas, and (c) jejunum. The time to peak aortic enhancement was linearly correlated to times to peak enhancement of the liver, pancreas, and jejunum (r = 0.69, 0.86, and 0.80, respectively, all P < .001). The correlation between the times to peak aortic and hepatic enhancement was not as strong as that between peak aortic and either peak pancreatic (P < .05) or jejunal (P < .001) enhancement.

 
In multivariate linear regression analysis, the times to peak enhancement of the liver, pancreas, and jejunum were all positively and linearly correlated with that of the aorta (all P < .001). However, age, sex, and presence of heart disease were not significant independent predictors of times to peak enhancement of the liver, pancreas, and jejunum when time to peak aortic enhancement was included in the model. In other words, inclusion of demographic information did not improve the ability to predict time to peak organ enhancement beyond what could be predicted by using the time to peak aortic enhancement alone.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
Our results show that there is wide interpatient variability in the times to peak enhancement of the aorta, liver, pancreas, and jejunum. More importantly, we show that the length of time to peak enhancement of the liver, pancreas, and jejunum increases linearly with that of the aorta. In other words, a longer time to peak aortic enhancement can be used to predict a proportionally longer time to peak visceral enhancement. These results imply that scan delays that are proportional to the length of the time to peak aortic enhancement may improve the reproducibility and quality of contrast material–enhanced MR imaging of target abdominal organs in daily practice.

The most precise determination of the time to peak enhancement of a given organ by using a timing bolus would be obtained by placing an ROI directly on the organ of interest. Potentially, such an approach may be useful for the liver, as that organ is fairly large and homogeneous in most patients. However, placement of an ROI on the pancreas and bowel wall can be labor intensive due to the relatively narrow diameter of the organs and motion artifact due to respiration and would likely not be practical for routine imaging. In contrast, measurement of signal intensity–time curve from the aorta is simple because this structure is fairly fixed even with patient respiration and enhances homogeneously and intensely with contrast material administration.

Also, the time to peak aortic enhancement may be particularly useful for determining scan delays for the pancreas and jejunum because the times to peak enhancement for the pancreas and jejunum were more highly correlated than that of the liver with respect to the time to peak aortic enhancement. This finding may be explained by the fact that the blood supply to the pancreas and jejunum is entirely from arterial flow, but the blood supply to the liver is a combination of venous and arterial (75%–80% from the portal vein vs 20%–25% from the hepatic artery). Given the dual blood supply of the liver, the time to peak hepatic enhancement is likely influenced by several other considerations including the circulation time of blood in the bowel and spleen, the extent of portal hypertension, and the arterial fraction of the hepatic inflow. Nevertheless, we did find a linear relationship between the times to peak aortic and hepatic enhancement, suggesting that the time to peak aortic enhancement is a reasonable means with which to predict the time to peak hepatic enhancement.

Researchers in prior studies who looked at scan delay optimization for imaging visceral organs have primarily reported on two methods: (a) use of a fixed scan delay and (b) addition of a fixed image delay to either the peak aortic enhancement time or after a threshold aortic enhancement was reached. In both methods, conclusions regarding optimal scan delays were determined by using images of either a single group of patients with a few set scan delays (11,13,14,34–38) or a few patient groups, each imaged with slightly different sets of scan delays (3,34).

Investigators in prior studies who assessed fixed scan delays after the start of contrast material injection did not account for interpatient variations in time to peak aortic enhancement (reported range, 9–37 seconds) (29,39). These researchers reported a range of optimal enhancement times of 50–90 seconds for the liver (8,35,38,40) and 20–60 seconds for the pancreas (11,13,14,36). These wide ranges are similar to the interquartile ranges in our study for the liver (29.2–96.6 seconds) and pancreas (18.3–53.0 seconds), and our findings build upon the prior work by showing that the interpatient variation can be predicted on the basis of measurement of the time to peak aortic enhancement.

Investigators in prior reports have accounted for patient-specific arrival time of contrast material in the aorta in their scan delays by adding a fixed amount of time to the test bolus or automatic bolus triggering to detect peak or threshold aortic enhancement, respectively (4,28–30,34,37,39,41–43). However, by adding a fixed rather than proportionally lengthened amount of time to the time to peak aortic enhancement as the scan delay, these prior methods do not account for the longer time to organ enhancement that we observed in patients that have a longer aortic time to peak enhancement. Notably, some studies (44,45) on these methods have noted variability in the success of capturing adequate visceral organ enhancement.

In our study, we only reported data on the relationship of aortic time to peak enhancement to hepatic, pancreatic, and jejunal times to peak enhancement and do not assess the value of proportionally adjusting scan time delays to the time to peak aortic enhancement in actual clinical MR or CT examinations. However, our results are encouraging in that they show a simple relationship between the time to peak enhancement of the aorta to those of the viscera and therefore enable a potentially improved method for capturing images at a more appropriate time after contrast material injection. It should be noted that many variables can affect the time to peak enhancement of the aorta and abdominal organs, and we evaluated only a few. Faster injection rates have been shown to yield earlier times to peak enhancement of the aorta (46–48) and liver (47,49).

Also, longer injection durations, such as those of full-dose contrast material administration, will lengthen the time to peak enhancement (19). Findings in some studies (50–52) suggest that variations in peak aortic times and enhancements can be decreased by using a fixed injection duration with adjustment of flow velocity on the basis of patient size. However, these studies still showed substantial interpatient variation (50–52), and alternative imaging delay techniques were recommended (30). Our study did not assess these factors, and further work will be needed to refine methods of scan delay optimization on the basis of injection rate and duration.

Other variables that can affect the time to peak enhancement include patient physiologic factors such as size, weight, cardiac output, metabolic status (35,37), and organ-specific disease. Our preliminary results show that these considerations did not contribute additional information beyond the time to peak aortic enhancement for predicting the time to peak visceral organ enhancement.

Patient-specific imaging delays from timing bolus studies have been evaluated for optimal imaging of the arterial phase of the liver for the detection of hypervascular lesions (7,9,10,27,29,39,53–55). These studies were performed with a temporal resolution of up to 60 seconds (1 second per image) (27) in up to 201 patients (mean, 77 patients; range, 29–201 patients) (53). Our study builds upon this work by presenting data for additional organs and showing the time to peak hepatic enhancement, which generally occurs in the portal venous phase of enhancement rather than in the arterial phase.

Potentially, imaging during the time of peak organ enhancement may improve our ability to detect hypovascular lesions, such as adenocarcinomas, which have been problematic in the pancreas (11–14,36,39). Similarly, as MR enterography develops, more precise timing of imaging may help evaluate inflammatory bowel disease and detect tumors.

Unfortunately, little has been published regarding improvement in lesion detection or lesion conspicuity with optimized imaging delays (3,5–7,9,10,56). Assessment of changes in lesion detection with scan time optimization is still based largely on expert opinion and a priori assumptions, and future work will be needed to show the importance of such optimization in patient care. We hope our findings will help lay a foundation for future studies to assess the clinical value of proportionally lengthened image delays for organ- and patient-specific abdominal imaging.

Our study had several limitations. First, it was focused primarily on describing the relationship between times to peak visceral and aortic enhancement, so we did not use our results to perform MR imaging with scan delays for optimization of organ parenchymal enhancement.

Second, we had a limited number of patients with known visceral organ disease; therefore, we were not able to determine whether specific diseases affect the time to peak visceral enhancement. Such assessments will require much larger sample sizes in the future.

Third, in our study, we assessed only timing boluses. Since full-dose contrast material injections involve larger volumes of contrast material given over a longer duration, the times to peak enhancement for these injections will be longer than those of the small timing boluses. Similarly, contrast material injections of different rates will result in different times to peak enhancement.

Finally, we could measure time to peak jejunal enhancement in only 66 of 141 patients due to both the narrow jejunal diameter and motion artifact from respiration and peristalsis, which frequently moved the jejunum out of the field of view.

In conclusion, we found that the times to peak enhancement of the liver, pancreas, and jejunum are linearly related to that of the aorta, potentially allowing patient- and organ-specific scan delay optimization at contrast-enhanced MR imaging.


   ADVANCES IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
IMPLICATIONS FOR PATIENT CARE
 References
 


   IMPLICATIONS FOR PATIENT CARE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
References
 


   FOOTNOTES
 

Abbreviations: ROI = region of interest

Author contributions: Guarantor of integrity of entire study, B.M.Y.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, L.L.C., B.M.Y.; clinical studies, all authors; statistical analysis, L.L.C., B.M.Y.; and manuscript editing, L.L.C., B.N.J., F.V.C., B.M.Y.

Authors stated no financial relationship to disclose.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 

  1. Mirowitz SA, Gutierrez E, Lee JK, Brown JJ, Heiken JP. Normal abdominal enhancement patterns with dynamic gadolinium-enhanced MR imaging. Radiology 1991;180:637–640. [Abstract/Free Full Text]
  2. Frederick MG, McElaney BL, Singer A, et al. Timing of parenchymal enhancement on dual-phase dynamic helical CT of the liver: how long does the hepatic arterial phase predominate? AJR Am J Roentgenol 1996;166:1305–1310.
  3. Goshima S, Kanematsu M, Kondo H, et al. MDCT of the liver and hypervascular hepatocellular carcinomas: optimizing scan delays for bolus-tracking techniques of hepatic arterial and portal venous phases. AJR Am J Roentgenol 2006;187:W25–W32. [Abstract/Free Full Text]
  4. Kim T, Murakami T, Hori M, et al. Small hypervascular hepatocellular carcinoma revealed by double arterial phase CT performed with single breath-hold scanning and automatic bolus tracking. AJR Am J Roentgenol 2002;178:899–904. [Abstract/Free Full Text]
  5. Materne R, Horsmans Y, Jamart J, Smith AM, Gigot JF, Van Beers BE. Gadolinium-enhanced arterial-phase MR imaging of hypervascular liver tumors: comparison between tailored and fixed scanning delays in the same patients. J Magn Reson Imaging 2000;11:244–249. [CrossRef][Medline]
  6. Murakami T, Kim T, Kawata S, et al. Evaluation of optimal timing of arterial phase imaging for the detection of hypervascular hepatocellular carcinoma by using triple arterial phase imaging with multidetector-row helical computed tomography. Invest Radiol 2003;38:497–503. [CrossRef][Medline]
  7. Shinozaki K, Yoshimitsu K, Irie H, et al. Comparison of test-injection method and fixed-time method for depiction of hepatocellular carcinoma using dynamic steady-state free precession magnetic resonance imaging. J Comput Assist Tomogr 2004;28:628–634. [CrossRef][Medline]
  8. Silverman PM, O'Malley J, Tefft MC, Cooper C, Zeman RK. Conspicuity of hepatic metastases on helical CT: effect of different time delays between contrast administration and scanning. AJR Am J Roentgenol 1995;164:619–623. [Abstract/Free Full Text]
  9. Van Beers BE, Materne R, Lacrosse M, et al. MR imaging of hypervascular liver tumors: timing optimization during the arterial phase. J Magn Reson Imaging 1999;9:562–567. [CrossRef][Medline]
  10. Yu JS, Kim KW, Jo BJ, et al. Test-bolus injection for optimization of arterial phase imaging during contrast-enhanced hepatic MR imaging. Yonsei Med J 2000;41:459–467. [Medline]
  11. Boland GW, O'Malley ME, Saez M, Fernandez-del-Castillo C, Warshaw AL, Mueller PR. Pancreatic-phase versus portal vein-phase helical CT of the pancreas: optimal temporal window for evaluation of pancreatic adenocarcinoma. AJR Am J Roentgenol 1999;172:605–608. [Abstract/Free Full Text]
  12. Diehl SJ, Lehmann KJ, Sadick M, Lachmann R, Georgi M. Pancreatic cancer: value of dual-phase helical CT in assessing resectability. Radiology 1998;206:373–378. [Abstract/Free Full Text]
  13. Graf O, Boland GW, Warshaw AL, Fernandez-del-Castillo C, Hahn PF, Mueller PR. Arterial versus portal venous helical CT for revealing pancreatic adenocarcinoma: conspicuity of tumor and critical vascular anatomy. AJR Am J Roentgenol 1997;169:119–123. [Abstract/Free Full Text]
  14. Lu DS, Vedantham S, Krasny RM, Kadell B, Berger WL, Reber HA. Two-phase helical CT for pancreatic tumors: pancreatic versus hepatic phase enhancement of tumor, pancreas, and vascular structures. Radiology 1996;199:697–701. [Abstract/Free Full Text]
  15. Bae KT, Heiken JP, Brink JA. Aortic and hepatic contrast medium enhancement at CT. II. Effect of reduced cardiac output in a porcine model. Radiology 1998;207:657–662.
  16. Bae KT, Heiken JP, Brink JA. Aortic and hepatic contrast medium enhancement at CT. I. Prediction with a computer model. Radiology 1998;207:647–655.
  17. Francois CJ, Shors SM, Bonow RO, Finn JP. Analysis of cardiopulmonary transit times at contrast material-enhanced MR imaging in patients with heart disease. Radiology 2003;227:447–452. [Abstract/Free Full Text]
  18. Paulson EK, Fisher AJ, DeLong DM, Parker DD, Nelson RC. Helical liver CT with computer-assisted bolus-tracking technology: is it possible to predict which patients will not achieve a threshold of enhancement? Radiology 1998;209:787–792. [Abstract/Free Full Text]
  19. Bae KT. Peak contrast enhancement in CT and MR angiography: when does it occur and why? pharmacokinetic study in a porcine model. Radiology 2003;227:809–816. [Abstract/Free Full Text]
  20. Earls JP, Rofsky NM, DeCorato DR, Krinsky GA, Weinreb JC. Breath-hold single-dose gadolinium-enhanced three-dimensional MR aortography: usefulness of a timing examination and MR power injector. Radiology 1996;201:705–710. [Abstract/Free Full Text]
  21. Foo TK, Saranathan M, Prince MR, Chenevert TL. Automated detection of bolus arrival and initiation of data acquisition in fast, three-dimensional, gadolinium-enhanced MR angiography. Radiology 1997;203:275–280. [Abstract/Free Full Text]
  22. Hany TF, McKinnon GC, Leung DA, Pfammatter T, Debatin JF. Optimization of contrast timing for breath-hold three-dimensional MR angiography. J Magn Reson Imaging 1997;7:551–556. [Medline]
  23. Prince MR, Chenevert TL, Foo TK, Londy FJ, Ward JS, Maki JH. Contrast-enhanced abdominal MR angiography: optimization of imaging delay time by automating the detection of contrast material arrival in the aorta. Radiology 1997;203:109–114. [Abstract/Free Full Text]
  24. Prince MR, Narasimham DL, Stanley JC, et al. Breath-hold gadolinium-enhanced MR angiography of the abdominal aorta and its major branches. Radiology 1995;197:785–792. [Abstract/Free Full Text]
  25. Cademartiri F, Nieman K, van der Lugt A, et al. Intravenous contrast material administration at 16-detector row helical CT coronary angiography: test bolus versus bolus-tracking technique. Radiology 2004;233:817–823. [Abstract/Free Full Text]
  26. van Hoe L, Marchal G, Baert AL, Gryspeerdt S, Mertens L. Determination of scan delay time in spiral CT-angiography: utility of a test bolus injection. J Comput Assist Tomogr 1995;19:216–220. [Medline]
  27. Earls JP, Rofsky NM, DeCorato DR, Krinsky GA, Weinreb JC. Hepatic arterial-phase dynamic gadolinium-enhanced MR imaging: optimization with a test examination and a power injector. Radiology 1997;202:268–273. [Abstract/Free Full Text]
  28. Hussain HK, Londy FJ, Francis IR, et al. Hepatic arterial phase MR imaging with automated bolus-detection three-dimensional fast gradient-recalled-echo sequence: comparison with test-bolus method. Radiology 2003;226:558–566. [Abstract/Free Full Text]
  29. Kanematsu M, Semelka RC, Matsuo M, et al. Gadolinium-enhanced MR imaging of the liver: optimizing imaging delay for hepatic arterial and portal venous phases—a prospective randomized study in patients with chronic liver damage. Radiology 2002;225:407–415. [Abstract/Free Full Text]
  30. Kim MJ, Chung YE, Kim KW, et al. Variation of the time to aortic enhancement of fixed-duration versus fixed-rate injection protocols. AJR Am J Roentgenol 2006;186:185–192. [Abstract/Free Full Text]
  31. Mehnert F, Pereira PL, Trubenbach J, Kopp AF, Claussen CD. Biphasic spiral CT of the liver: automatic bolus tracking or time delay? Eur Radiol 2001;11:427–431. [CrossRef][Medline]
  32. Shimizu T, Misaki T, Yamamoto K, Sueyoshi K, Narabayashi I. Helical CT of the liver with computer-assisted bolus-tracking technology: scan delay of arterial phase scanning and effect of flow rates. J Comput Assist Tomogr 2000;24:219–223. [CrossRef][Medline]
  33. Pinheiro JC, Bates DM. Extending the basic linear mixed-effects model. In: Mixed-effects models in S and S-PLUS. New York, NY: Springer Verlag, 2000; 206–225.
  34. Chung YE, Kim KW, Kim JH, et al. Optimal delay time for the hepatic parenchymal enhancement at the multidetector CT examination. J Comput Assist Tomogr 2006;30:182–188. [CrossRef][Medline]
  35. Herts BR, Paushter DM, Einstein DM, Zepp R, Friedman RA, Obuchowski N. Use of contrast material for spiral CT of the abdomen: comparison of hepatic enhancement and vascular attenuation for three different contrast media at two different delay times. AJR Am J Roentgenol 1995;164:327–331. [Abstract/Free Full Text]
  36. Hollett MD, Jorgensen MJ, Jeffrey RB Jr. Quantitative evaluation of pancreatic enhancement during dual-phase helical CT. Radiology 1995;195:359–361. [Abstract/Free Full Text]
  37. Silverman PM, Roberts S, Tefft MC, et al. Helical CT of the liver: clinical application of an automated computer technique, SmartPrep, for obtaining images with optimal contrast enhancement. AJR Am J Roentgenol 1995;165:73–78. [Abstract/Free Full Text]
  38. Vignaux O, Legmann P, Coste J, Hoeffel C, Bonnin A. Cirrhotic liver enhancement on dual-phase helical CT: comparison with noncirrhotic livers in 146 patients. AJR Am J Roentgenol 1999;173:1193–1197. [Abstract/Free Full Text]
  39. Kanematsu M, Shiratori Y, Hoshi H, Kondo H, Matsuo M, Moriwaki H. Pancreas and peripancreatic vessels: effect of imaging delay on gadolinium enhancement at dynamic gradient-recalled-echo MR imaging. Radiology 2000;215:95–102. [Abstract/Free Full Text]
  40. Baron RL. Understanding and optimizing use of contrast material for CT of the liver. AJR Am J Roentgenol 1994;163:323–331. [Abstract/Free Full Text]
  41. Dinkel HP, Fieger M, Knupffer J, Moll R, Schindler G. Optimizing liver contrast in helical liver CT: value of a real-time bolus-triggering technique. Eur Radiol 1998;8:1608–1612. [CrossRef][Medline]
  42. Kopka L, Rodenwaldt J, Fischer U, Mueller DW, Oestmann JW, Grabbe E. Dual-phase helical CT of the liver: effects of bolus tracking and different volumes of contrast material. Radiology 1996;201:321–326. [Abstract/Free Full Text]
  43. Murakami T, Onishi H, Mikami K, et al. Determining the optimal timing for early arterial phase hepatic CT imaging by measuring abdominal aortic enhancement in variable contrast injection protocols. J Comput Assist Tomogr 2006;30:206–211. [CrossRef][Medline]
  44. Itoh S, Ikeda M, Achiwa M, Satake H, Iwano S, Ishigaki T. Late-arterial and portal-venous phase imaging of the liver with a multislice CT scanner in patients without circulatory disturbances: automatic bolus tracking or empirical scan delay? Eur Radiol 2004;14:1665–1673. [Medline]
  45. Sandstede JJ, Tschammler A, Beer M, Vogelsang C, Wittenberg G, Hahn D. Optimization of automatic bolus tracking for timing of the arterial phase of helical liver CT. Eur Radiol 2001;11:1396–1400. [CrossRef][Medline]
  46. Bae KT, Heiken JP, Brink JA. Aortic and hepatic peak enhancement at CT: effect of contrast medium injection rate—pharmacokinetic analysis and experimental porcine model. Radiology 1998;206:455–464. [Abstract/Free Full Text]
  47. Mitsuzaki K, Yamashita Y, Ogata I, Nishiharu T, Urata J, Takahashi M. Multiple-phase helical CT of the liver for detecting small hepatomas in patients with liver cirrhosis: contrast-injection protocol and optimal timing. AJR Am J Roentgenol 1996;167:753–757. [Abstract/Free Full Text]
  48. Platt JF, Reige KA, Ellis JH. Aortic enhancement during abdominal CT angiography: correlation with test injections, flow rates, and patient demographics. AJR Am J Roentgenol 1999;172:53–56. [Abstract/Free Full Text]
  49. Garcia PA, Bonaldi VM, Bret PM, Liang L, Reinhold C, Atri M. Effect of rate of contrast medium injection on hepatic enhancement at CT. Radiology 1996;199:185–189. [Abstract/Free Full Text]
  50. Awai K, Hori S. Effect of contrast injection protocol with dose tailored to patient weight and fixed injection duration on aortic and hepatic enhancement at multidetector-row helical CT. Eur Radiol 2003;13:2155–2160. [CrossRef][Medline]
  51. Awai K, Hiraishi K, Hori S. Effect of contrast material injection duration and rate on aortic peak time and peak enhancement at dynamic CT involving injection protocol with dose tailored to patient weight. Radiology 2004;230:142–150. [Abstract/Free Full Text]
  52. Kanematsu M, Goshima S, Kondo H, et al. Optimizing scan delays of fixed duration contrast injection in contrast-enhanced biphasic multidetector-row CT for the liver and the detection of hypervascular hepatocellular carcinoma. J Comput Assist Tomogr 2005;29:195–201. [CrossRef][Medline]
  53. Awai K, Takada K, Onishi H, Hori S. Aortic and hepatic enhancement and tumor-to-liver contrast: analysis of the effect of different concentrations of contrast material at multi–detector row helical CT. Radiology 2002;224:757–763. [Abstract/Free Full Text]
  54. Murakami T, Kim T, Takamura M, et al. Hypervascular hepatocellular carcinoma: detection with double arterial phase multi–detector row helical CT. Radiology 2001;218:763–767. [Abstract/Free Full Text]
  55. Noguchi Y, Murakami T, Kim T, et al. Detection of hypervascular hepatocellular carcinoma by dynamic magnetic resonance imaging with double-echo chemical shift in-phase and opposed-phase gradient echo technique: comparison with dynamic helical computed tomography imaging with double arterial phase. J Comput Assist Tomogr 2002;26:981–987. [CrossRef][Medline]
  56. Kim MJ, Choi JY, Lim JS, et al. Optimal scan window for detection of hypervascular hepatocellular carcinomas during MDCT examination. AJR Am J Roentgenol 2006;187:198–206. [Abstract/Free Full Text]




This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
2451061585v1
245/3/779    most recent
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Chu, L. L.
Right arrow Articles by Yeh, B. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Chu, L. L.
Right arrow Articles by Yeh, B. M.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
RADIOLOGY RADIOGRAPHICS RSNA JOURNALS ONLINE