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Genitourinary Imaging |
1 From the Department of Radiology, Hospital of the University of Pennsylvania, 3400 Spruce St, Philadelphia, PA 19104. Received April 8, 1998; revision requested June 29; revision received August 26; accepted October 20. Address reprint requests to B.A.B.
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Abstract |
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 TOP Abstract IntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: Seventy-five patients underwent bolus tracking of contrast material followed by helical renal CT. In 50 patients, 150 mL of 60% iodinated contrast material (iohexol or iothalamate meglumine) was injected at either 2 mL/sec (25 patients [group 1]) or 3 mL/sec (25 patients [group 2]). In 25 patients who had previously undergone nephrectomy, 100 mL of 60% iodinated contrast material was injected at 3 mL/sec (group 3). Nephrographic phase onset was determined by visually assessing the transition to a homogeneous nephrogram during a monitoring scan series starting 40 seconds after injection.
RESULTS: Nephrographic phase onset ranged from 60 to 136 seconds (mean, 89 seconds ± 17 [± SD]). Statistically significant differences in mean onset times were observed among groups 1 (103 seconds ± 12), 2 (91 seconds ± 16), and 3 (75 seconds ± 9) (P < .001). Multiple regression analysis showed patient age, contrast material volume, and injection rate to be independent predictors of nephrographic phase onset. Contrast material volume, patient age, and patient weight were independent predictors of the degree of renal enhancement.
CONCLUSION: Nephrographic phase onset is highly dependent on methods of contrast material administration and patient characteristics.
Index terms: Computed tomography (CT), helical, 81.12114, 81.12115, 81.30 • Computed tomography (CT), technology, 81.12114, 81.12115, 81.30 • Kidney neoplasms, CT, 81.12114, 81.12115 • Kidney neoplasms, diagnosis, 81.12114, 81.12115
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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3.0-cm) renal masses with conventional computed tomography (CT) may be problematic because of respiratory misregistration and partial volume averaging effects (1,2). Advances in helical CT technology have largely overcome these limitations because helical scanning now permits volumetric data acquisition within a single breath hold, rapid imaging during peak levels of contrast enhancement, elimination of respiratory misregistration artifacts, minimization of motion artifacts, and production of overlapping images without additional radiation exposure (3–7). As a result, helical CT has supplanted conventional CT as the best technique to demonstrate subtle tumoral enhancement, mural nodularity, and internal septa—key imaging findings used to differentiate benign from malignant lesions (8). Recent studies have explored the potential role of multiphasic scanning during the corticomedullary and nephrographic phases of renal enhancement (9–13). These investigations have shown nephrographic phase imaging to be superior to corticomedullary phase imaging for lesion detection and to be either superior or equal to corticomedullary phase imaging for lesion characterization. Therefore, most authorities now recommend that renal helical CT studies include at least one data acquisition during the homogeneous nephrographic phase of renal enhancement (2,10–15). The onset of the nephrographic phase is commonly stated to occur at approximately 90–100 seconds after the start of contrast material injection; however, to the best of our knowledge, this onset time has not been systematically investigated (2,8,9,15).
At our institution, we have observed substantial variation among patients in the time needed to achieve a homogeneous nephrogram on dedicated renal CT studies. Bolus-tracking software designed to quantitatively and qualitatively monitor organ contrast enhancement (SMARTPREP; GE Medical Systems, Milwaukee, Wis) has facilitated the optimization of hepatic helical CT by individualizing scan initiation delay times (16–18). We hypothesized that the bolus-tracking method could also optimize dedicated renal CT and be used to trigger helical renal CT scanning at the completion of the heterogeneous corticomedullary phase of enhancement.
The major objectives of this study were to evaluate the feasibility of using a bolus-tracking technique to identify the onset of the nephrographic phase, to determine the effect of varying the contrast material volume and injection rate on nephrographic phase onset, and to assess the degree of patient variability in the time to nephrographic phase onset.
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MATERIALS AND METHODS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Patients were entered into one of three groups with different protocols for intravenous injection of 60% iodinated contrast material, either iothalamate meglumine (Conray 60; Mallinckrodt Medical, St Louis, Mo) or iohexol (Omnipaque 300; Nycomed, Princeton, NJ) (Table 1). Patients referred for renal mass evaluation received 150 mL (42–45 g of iodine) of contrast material injected at a rate of either 2 mL/sec (group 1 [25 patients]) or 3 mL/sec (group 2 [25 patients]). Patients who had previously undergone nephrectomy received 100 mL (28–30 g of iodine) of contrast material injected at a rate of 3 mL/sec (group 3 [25 patients]).
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Nursing personnel randomly assigned patients to groups 1 and 2, with the exception of a single patient with a 22-gauge venous cannula who was arbitrarily placed in group 1 and examined with the slower injection rate (2 mL/sec). Patients in group 3 received a smaller bolus of contrast material than patients in groups 1 and 2 because the standard practice at our institution is to administer a reduced iodine load (100 mL) to patients who have previously undergone nephrectomy.
The following scanning technique was used in all patients: Initial nonenhanced images were obtained through the kidney or kidneys with a cluster acquisition technique (five contiguous axial scans per 9-second breath hold, with 8 seconds between clusters) on helical CT scanners (HiSpeed Advantage; GE Medical Systems) operated in a conventional nonhelical mode (section collimation, 5 mm; peak kilovoltage, 120 kVp; tube current, 300–340 mA; and scanning time, 1 second).
The nonenhanced data set was then reviewed by a staff physician who checked for potential respiratory misregistration between clusters. If misregistration was present (seen in one of 75 patients), additional nonenhanced images were obtained through the region of interest to ensure adequate renal coverage. The nonenhanced data set was obtained with a conventional technique because software and hardware limitations inherent in our CT scanners when this study was performed prevented us from scanning the patients' kidneys twice (before and after contrast material injection) with a high–milliampere-second helical technique.
A series of low–radiation-dose monitoring scans was then obtained with scanner software (SMARTPREP) designed to determine individualized scanning delay times (15–17). A single nonenhanced scan was acquired at the approximate level of the renal hilum, and a small baseline region of interest was placed over the aorta and the lateral aspect of the visualized renal cortex.
At 40 seconds after the start of the injection, up to 10 low-dose monitoring scans (120 kVp; 40 mA; 0.6-second scanning time; 9-second interscan delay; 6–7-second mean reconstruction time; 256 x 256 matrix) were obtained at this anatomic level. The scanner software automatically displayed updated, sequential contrast-enhanced images of the kidney or kidneys adjacent to the nonenhanced baseline image, which enabled visual qualitative assessment of the evolution of the renal nephrogram or nephrograms from 40 to 127 seconds after injection. Although not used directly in this study, quantitative data regarding enhancement of the aorta and kidney were simultaneously presented in graphic format.
The window width and level were narrowed by the operator to facilitate visualization of the nephrogram and discrimination of corticomedullary differentiation. The monitoring scan images were observed by both a technologist and an attending radiologist (B.A.B., J.E.J.) or body-imaging fellow, who manually "triggered" acquisition of a helical renal CT data set once corticomedullary differentiation was no longer visualized and the renal nephrogram or nephrograms appeared homogeneously enhanced (Fig 1). In patients in whom nephrogram asymmetry was seen, triggering occurred when the normal (nondelayed) kidney revealed a homogeneous nephrogram.
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Enhanced renal helical CT was performed with the same scanning parameters (section collimation, peak kilovoltage, tube current, scanning time, and scanning field of view) that were chosen for each patient's nonenhanced data acquisition. Helical pitch varied from 1.6:1 to 1.0:1 (mean pitch value, 1.2:1) to enable renal scanning within a single breath hold (<25–30 seconds), with z-axis coverage based on review of nonenhanced imaging data. All helical images were reconstructed at contiguous, nonoverlapping 5-mm intervals. The remaining portion of the abdomen was scanned with 7-mm collimation with an axial-cluster acquisition technique. The summary display of each patient's monitoring series was "screen-saved" and filmed for hard-copy review, along with the individual monitoring scans, which were filmed with narrow window widths and levels to facilitate nephrographic interpretation.
Nephrographic phase onset was determined by two radiologists (B.A.B., J.E.J.) experienced in body CT who performed a consensual review of each patient's imaging data. For each patient, the monitoring scans were reviewed retrospectively to verify that the image used to trigger the helical data acquisition showed a homogeneous nephrogram without apparent corticomedullary differentiation. If a homogeneous nephrogram was not present on the 10 monitoring scans, the nephrographic phase onset time was assigned a value of 136 seconds (127-second maximal observational time plus a 9-second interscan delay) to indicate that the transition from a heterogeneous to a homogeneous nephrogram was delayed and not identified during the 127-second monitoring period.
In five patients, the readers consensually agreed that the transition to a homogeneous nephrogram occurred on the monitoring scan that was obtained immediately prior to the scan prospectively used to trigger helical data acquisition. In these patients, "corrected" nephrographic phase onset times were used for data analysis to ensure that the data reflected the actual times that the nephrographic phase began.
The nephrographic phase onset data were analyzed at cutoff intervals of 70, 80, 90, 100, 110, and 120 seconds to determine if renal enhancement was in the corticomedullary phase or the homogeneous nephrographic phase at various standard delay times that have been suggested for nephrographic phase imaging of the kidneys.
Nephrographic phase parenchymal enhancement was independently evaluated by a third radiologist (P.R.), who measured renal cortical attenuation values on the contrast-enhanced helical CT images. Renal enhancement was calculated by subtracting the baseline region of interest obtained from the nonenhanced kidney on the initial nonenhanced monitoring scan from the mean of three separate regions of interests (region of interest 
0.4 cm2) that were placed over peripheral renal cortex at the upper pole of each patient's most proximal kidney on the contrast-enhanced images. The time to begin and complete renal scanning was also determined in each patient by correlating the data acquisition times posted on the most proximal and distal renal CT images with the postinjection time data presented in the monitoring series summary display.
The unpaired Student t test was used to compare continuous variables between groups, including age and weight differences. The 
2 analysis was used to detect differences between groups in categoric variables such as sex, collecting system visualization, and contrast material. The Mann-Whitney U test was applied to identify significant differences among groups for nephrographic phase onset time, times to begin and complete renal scanning, and renal enhancement. Analysis of variance was used to determine the effect of the type of contrast material on the degree of enhancement.
Stepwise linear regression analysis was then applied to the entire data set and was used to analyze in multivariate fashion four independent parameters (patient age, patient weight, injection rate, and contrast material volume) to determine if these variables served as independent predictors of nephrographic phase onset time and renal parenchymal enhancement. The regression coefficients for these four independent parameters were calculated from the linear regression analysis. These results were used to generate scatterplots for nephrographic phase onset time (predicted versus actual time) and renal enhancement (predicted versus actual enhancement).
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RESULTS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Nephrographic phase imaging data are presented in Tables 2 and 3. Mean nephrographic phase onset time was 89 seconds ± 17 for the entire study population and ranged from 60 to 136 seconds (Table 2). The transition to a homogeneous nephrogram was not identified during bolus tracking in three patients (one patient in group 1 and two patients in group 2), who were scored as having onset times of 136 seconds to reflect the presence of prolonged corticomedullary differentiation (Fig 2). Review of the medical records revealed that these three patients had known cardiac disease complicated by congestive heart failure. Retrospective review of the monitoring scan data revealed that helical CT was triggered 9 seconds (one image) late in five (7%) of the 75 patients. No studies were believed to be triggered prematurely.
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Because initiation of helical renal CT scanning was directly dependent on nephrographic phase triggering, similar temporal trends were observed with regard to mean times to initiate and complete renal CT scanning. As length of injection increased from 33 to 75 seconds, mean renal scan initiation times increased from 94 seconds ± 11 to 119 seconds ± 12, while mean scan completion times increased from 116 seconds ± 10 to 142 seconds ± 12. Scan completion time ranged from a minimum of 90 seconds to a maximum of 178 seconds. No relationship was identified between nephrographic phase onset and the type of contrast material injected.
The data in Table 3 demonstrate the phase of renal enhancement encountered at various cutoff times. These results enable one to identify the number of patients who would have been correctly scanned during the nephrographic phase with standard helical CT delay times of 70, 80, 90, 100, 110, and 120 seconds. For example, use of a standard 90-second scanning delay would have enabled initiation of helical renal CT during the nephrographic phase in only 65% (49 of 75 patients) in this study. Although this delay would have been optimal for 96% (24 of 25 patients) of group 3, it would have resulted in premature corticomedullary phase scanning in 20% (five of 25 patients) of group 2 and 80% (20 of 25 patients) of group 1. In contrast, the use of a 120-second scanning delay would have resulted in nephrographic phase imaging in 96% (24 of 25 patients), 92% (23 of 25 patients), and 100% (25 of 25 patients) of groups 1, 2, and 3, respectively.
Nephrographic phase enhancement data are shown in Table 2. Mean parenchymal enhancement exceeded 100 HU in all groups and ranged from 112 HU ± 22 (group 3) to 137 HU ± 31 (group 2). No significant differences in mean parenchymal enhancement were noted between patients in groups 1 and 2, whose injection protocols differed only by injection rate. Patients in group 2 demonstrated significantly greater mean parenchymal enhancement compared with patients in group 3 (P < .005). These injection protocols differed only by volume of contrast material (total iodine load) delivered. Although patients in group 1 demonstrated greater mean parenchymal enhancement compared with patients in group 3, this difference did not reach statistical significance (P = .12). These injection protocols differed with respect to both injection rate and contrast material volume (total iodine load) administered.
Patients examined with nonionic contrast material had significantly greater renal enhancement than that of patients examined with ionic contrast material (P < .001). Mean parenchymal enhancement levels for patients in groups 1, 2, and 3 were 164 HU ± 33, 182 HU ± 23, and 124 HU ± 22, respectively, for nonionic contrast material use and were 115 HU ± 21, 126 HU ± 22, and 109 HU ± 22, respectively, for ionic contrast material use.
Helical renal CT scanning was completed prior to visualization of the collecting system in 35 (47%) of 75 patients. The collecting system was at least partially visualized in 14 (56%) of 25 patients in group 1, in 16 (64%) of 25 patients in group 2, and in 10 (40%) of 25 patients in group 3. Although this trend initially suggested that patients who received a smaller contrast material volume may have been scanned at an earlier phase, no significant differences were noted between the groups when this variable was specifically tested (P = .2). Collecting system visualization was noted in all three patients with evidence of slow circulation times. No correlation was identified between collecting system visualization and the type of contrast material injected.
Results of the stepwise linear regression analysis are displayed in Table 4. Three independent variables (patient age, contrast material volume, and injection rate) were shown to be independent predictors of nephrographic phase onset. The time to nephrographic phase onset can be predicted by using the calculated regression coefficients and intercept point from the table with the following formula: nephrographic phase onset time = 57.428 sec + 0.469 sec/y (patient age) + 0.241 sec/mL (contrast material volume) - 10.795 sec2/mL (injection rate).
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Scatterplots for nephrographic phase onset time (predicted versus actual time) and renal enhancement (predicted versus actual enhancement) are shown in Figures 3 and 4, respectively. These plots demonstrate that although it is possible to statistically predict nephrographic phase onset and renal parenchymal enhancement, the predicted results on average may have little clinical value to the individual patient. Analysis of the vertical columns of the scatterplots reveals that the actual values may vary considerably, even for patients with the same predicted values. This reflects the underlying individual variability in both nephrographic phase onset and renal parenchymal enhancement that is not captured by the regression model.
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The corticomedullary phase begins as contrast material enters the cortical capillaries and peritubular spaces and filters into the proximal cortical tubules (20,21). Renal cortex can be differentiated from renal medulla at this stage because cortical vascularity is greater than that of the medulla and because contrast material has not yet reached the distal aspect of the renal tubules (20,22). The resultant CT nephrogram has been termed a cortical nephrogram.
The nephrographic phase begins as contrast material proceeds from the cortical vessels and extracellular-interstitial space and enters the loops of Henle and collecting tubules. This results in a homogeneous or tubular nephrogram in which corticomedullary differentiation is lost. The temporal limits of the nephrographic phase have not been clearly defined, and it may be prudent to subclassify this phase into early and late stages on the basis of the appearance of contrast material within the intrarenal collecting system. This modification of terminology is needed because the nephrographic and excretory phases of enhancement typically overlap when relatively large volumes of contrast material are administered with a mechanical power injector, as is the practice with current protocols for body CT.
With this suggested classification system, the early nephrographic phase concludes, and the late nephrographic phase begins, when caliceal enhancement occurs. The late nephrographic phase therefore parallels the excretory phase of enhancement. The late phase is initially characterized by a homogeneously intense nephrogram; however, the intensity of the nephrogram gradually declines during this phase as contrast material is continuously excreted into the collecting system.
Advances in helical CT technology now afford the radiologist the choice of performing a routine monophasic examination of the kidneys or a multiphasic study in which the kidneys are scanned during both the corticomedullary and nephrographic phases of enhancement. Dedicated renal CT studies are usually performed to detect and characterize a known or suspected renal abnormality. In most cases, this goal is best achieved by scanning the kidneys during the early nephrographic phase of renal enhancement. This is true for the reasons given in the following paragraphs.
Previous studies have demonstrated conclusively that detection of both cortical and medullary lesions is maximized in the nephrographic phase (9,11). This is especially true for small medullary lesions, which are poorly seen in the cortical nephrogram but are readily appreciated in the homogeneous nephrogram. As a result, radiologists report higher levels of diagnostic confidence for detecting renal lesions during the nephrographic phase of renal enhancement (10,12).
Characterization of renal lesions is based on the identification of key morphologic features such as tumoral enhancement, mural nodularity, calcification, and internal septation. Of these parameters, tumoral enhancement is most important. The unequivocal diagnosis of "tissue enhancement" is indicative of neovascularity and is the most critical factor in diagnosing a renal tumor (23).
Compelling evidence suggests that renal lesion enhancement is best assessed in the early nephrographic phase. Renal neoplasm enhancement has been shown to be time dependent and may not be evident in hypovascular tumors analyzed during the corticomedullary phase (13). Birnbaum et al (13) evaluated the enhancement characteristics of small renal masses and found that 15 (94%) of 16 renal neoplasms demonstrated progressive enhancement over time and displayed greater tumoral enhancement in the nephrographic phase compared with the corticomedullary phase. The single exception was a vascular neoplasm that was correctly characterized in both perfusion phases but showed greater enhancement in the corticomedullary phase (13).
If possible, renal CT scanning should be completed before contrast material is excreted within the collecting system (2). Accurate analysis of neoplasm enhancement is dependent on the reliability of CT attenuation values on both pre- and postcontrast scans. The quality of the CT scan may be degraded by beam-hardening artifacts generated from accumulated contrast material within the collecting system. Nonionic contrast material produces perceptibly greater enhancement of the collecting system and is especially problematic in this regard (24). This imaging pitfall may be avoided if renal helical CT data acquisition is performed during the early nephrographic phase, before the collecting system becomes intensely enhanced.
If one accepts the foregoing rationale that dedicated renal CT studies should be performed during the early nephrographic phase, the question faced by the practicing radiologist is when to begin such an examination. Previous reports (2,8,9,15,18) have indicated that the nephrographic phase begins anywhere from 70 to 100 seconds after injection. These investigators based these claims on either long-standing anecdotal experience or the results of CT enhancement studies in which the contrast material injection parameters varied widely.
In contrast, our study demonstrated that there is tremendous individual variability in the time required to achieve a homogeneous nephrogram. Although the mean nephrographic phase onset time was 89 seconds ± 17, this time varied from 60 to 136 seconds. Regression analysis showed this transition time to be highly dependent on the method of contrast material administration. Both the injection rate and the volume of contrast material delivered (total iodine load) were shown to be independent predictors of nephrographic phase onset time. Patient age was also shown to be an independent predictor of this time.
We believe that age may indirectly reflect the patient's cardiovascular status and that this would explain why increasing age correlated with longer time until nephrographic phase onset. This was certainly the case for three patients (age range, 73–82 years) with known cardiac disease who demonstrated prolonged corticomedullary differentiation throughout the SMARTPREP monitoring period and were assigned onset times of 136 seconds.
This study showed that the bolus-tracking method is both feasible and necessary to assess qualitatively the evolution of the renal nephrograms. This software enabled the CT operator to optimally initiate renal helical CT scanning by individualizing the scanning delay times to coincide with nephrographic phase onset.
Although our regression model can make a statistically significant prediction of nephrographic phase onset, this prediction has little clinical value on average to the individual patient because of the underlying variability in nephrographic phase onset that is not captured by the regression model. For example, although there is a clear relationship between predicted and actual nephrographic phase onset in the scatterplot in Figure 3, a high degree of variability in actual nephrographic phase onset remains among patients with the same predicted nephrographic phase onset time. This was clearly seen in the three patients in whom a homogeneous nephrogram was not demonstrated and whose scans were triggered after the monitoring period.
Nephrographic phase scanning was performed during high contrast enhancement in this study, with mean parenchymal enhancement exceeding 100 HU for all groups. Renal enhancement varied considerably and ranged from a low of 77 HU (low-dose protocol) to a high of 211 HU (high-dose protocol). Regression analysis revealed contrast material volume (total iodine load), patient age, and patient weight to be independent predictors of renal enhancement. No relationship between enhancement and injection rate was seen. Significantly greater renal enhancement was observed in patients examined with nonionic contrast material (P < .001).
As one would expect, patients in group 2 demonstrated significantly greater mean parenchymal enhancement compared with patients in group 3 (P < .005), and a similar trend (without statistical significance) was seen between patients in group 1 and those in group 3. These results emphasize the important differences in contrast material volume that existed between the injection protocols. Although patients in group 3 were significantly younger (P < .05) than their counterparts (positive correlation with enhancement), their mean renal enhancement was lower because these patients received 33% less contrast material than patients in groups 1 and 2.
Our study protocol dictated that helical CT scanning began at least 15–17 seconds after nephrographic phase onset actually occurred. This temporal delay resulted from multiple factors, which included a fixed delay time for monitoring scan reconstruction, a variable delay time needed for the technologist to react and for the scanner to transition to helical data acquisition, and a fixed preprogrammed scanning phase delay time that was chosen to enable proper gantry positioning and patient breath holding. The time from nephrographic phase onset to helical CT scanning should decrease in the future as improvements in bolus-tracking software become available that will enable the CT operator to react faster to an observed physiologic event.
Despite the inherent constraints of the software used in this study, renal CT data acquisition was completed during the early nephrographic phase in 47% (35 of 75 patients). Although the remaining studies extended into the late nephrographic phase, renal scanning was completed at a time when only minimal caliceal enhancement was noted and before there was intense enhancement of the collecting system.
The bolus-tracking images in this study were interpreted prospectively by both a CT technologist and either a staff radiologist or a fellow. This dual monitoring was done to minimize the chance of error while the CT technologists familiarized themselves with the normal evolutionary appearance of the renal nephrogram. In our experience, a learning curve for this application exists, and technologists require diligent training. Our technologists subsequently have learned to implement this scanning technique successfully without physician supervision.
Monophasic CT scanning in the nephrographic phase represents a niche application for helical CT in which the kidney is the primary organ of interest, and the goal of imaging is tumor detection and characterization. When used in conjunction with bolus-tracking software, scanning delay times may be individualized to guarantee optimized helical CT data acquisition in the early nephrographic phase. This imaging technique need not be limited to CT units that are incapable of multiphasic helical CT scanning (14). Our scanners have been upgraded since this study was performed and are now capable of performing multiple helical "runs" through the abdomen without compromise in radiologic technique (tube current).
We continue to use this scanning technique because we have found it to be invaluable when performing dedicated characterization studies of small renal masses, as well as surveillance studies in patients who have previously undergone partial or total nephrectomy for renal cell carcinoma. Many of these patients do not need to undergo multiphasic helical CT, with its attendant extra radiation exposure and increased film and archive expenses. The ability to monitor the evolution of the nephrogram is especially useful in patients with impaired cardiac function who may have delayed renal enhancement.
Premature scanning in the corticomedullary phase may result if fixed scanning delay times are used. This premature scanning may compromise lesion detection and characterization. This pitfall may be avoided by appropriately delaying helical CT data acquisition until onset of the nephrographic phase is confirmed visually. This technique does not hinder evaluation of the renal collecting system because excretory phase imaging can easily follow the dedicated nephrographic phase run.
It must be stressed that this technique should not be used in patients in whom another organ (eg, liver or pancreas) is of primary interest, in patients who require detailed evaluation of the renal arteries, or in patients in whom corticomedullary phase imaging is necessary. Early corticomedullary phase imaging may be helpful in identifying normal corticomedullary variants, such as prominent columns of Bertin and dromedary humps (13,14).
In summary, the results of this study demonstrated that there is considerable individual variation in the onset of the homogeneous nephrographic phase of renal enhancement. Regression analysis showed nephrographic phase onset to be highly dependent on the method of contrast material administration because both the injection rate and the volume of contrast material delivered (total iodine load) were shown to be independent predictors of this transition time.
Although it is possible to use a regression equation to predict statistically the mean nephrographic phase onset time for a subgroup of patients, the clinical applicability of that prediction is limited because of the inherent variability among patients in the subgroup (Fig 3). Consequently, the results of this study demonstrated that semiautomated bolus-tracking software is feasible and is superior to our regression model for qualitatively assessing the evolution of the renal nephrograms and for triggering helical data acquisition during the early nephrographic phase of renal enhancement.
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Footnotes |
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References |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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3.0 cm) renal parenchymal tumor: detection, diagnosis, and controversies. Radiology 1991; 179:307-317.This article has been cited by other articles:
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  H. Arakawa, T. Kohno, T. Hiki, and Y. Kaji CT Pulmonary Angiography and CT Venography: Factors Associated with Vessel Enhancement Am. J. Roentgenol., July 1, 2007; 189(1): 156 - 161. [Abstract] [Full Text] [PDF]
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 K. T. Bae, C. Tao, S. Gurel, C. Hong, F. Zhu, T. A. Gebke, M. Milite, and C. F. Hildebolt Effect of Patient Weight and Scanning Duration on Contrast Enhancement during Pulmonary Multidetector CT Angiography Radiology, February 1, 2007; 242(2): 582 - 589. [Abstract] [Full Text] [PDF]
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B. A. Birnbaum, D. D. Maki, D. P. Chakraborty, J. E. Jacobs, and J. S. Babb Renal Cyst Pseudoenhancement: Evaluation with an Anthropomorphic Body CT Phantom Radiology, October 1, 2002; 225(1): 83 - 90. [Abstract] [Full Text] [PDF]
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 A. Kawashima, C. M. Sandler, R. D. Ernst, E. P. Tamm, S. M. Goldman, and E. K. Fishman CT Evaluation of Renovascular Disease RadioGraphics, September 1, 2000; 20(5): 1321 - 1340. [Abstract] [Full Text] [PDF]
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D. D. Maki, B. A. Birnbaum, D. P. Chakraborty, J. E. Jacobs, B. M. Carvalho, and G. T. Herman Renal Cyst Pseudoenhancement: Beam-hardening Effects on CT Numbers Radiology, November 1, 1999; 213(2): 468 - 472. [Abstract] [Full Text]
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