Renal cyst pseudoenhancement: beam-hardening effects on CT numbers

Renal Cyst Pseudoenhancement: Influence of Multidetector CT Reconstruction Algorithm and Scanner Type in Phantom Model

PURPOSE

To prospectively determine the dependence of renal cyst pseudoenhancement on multidetector computed tomographic (CT) scanner type and convolution kernel in a phantom model.

MATERIALS AND METHODS

A customized anthropomorphic phantom was created to accept interchangeable 40-, 140-, and 240-HU renal inserts that contained stacked 0- and 50-HU cylindric cysts measuring 7, 10, and 15 mm in diameter. Each phantom and insert was scanned with five different multidetector CT scanners on five separate occasions by using 120 kVp, low and high tube current settings, 3.00-3.75-mm collimation, and standard and high-spatial-resolution kernels. A total of 2340 CT attenuation measurements were obtained by using standardized regions of interest. The effect of multidetector CT imaging regimen, tube current, cyst diameter, and renal attenuation on pseudoenhancement incidence was assessed by using generalized estimating equations based on a binary logistic regression model. Within this framework, a Bonferroni multiple comparison correction was used to assess pseudoenhancement frequency differences among imaging regimens.

RESULTS

Pseudoenhancement occurred in both 0- and 50-HU cysts; was significantly correlated with multidetector CT imaging regimen (P<.0001), cyst diameter (P<.0001), and renal attenuation (P<or=.032); and was independent of tube current (P>.3). When convolution kernels on specific scanners were compared, significant differences (P<.04) between kernels were identified with all five scanners in terms of observed pseudoenhancement incidence. Generational differences in equipment were noted, with pseudoenhancement incidence ranging from 1.7% to 8.3%, 1.7% to 16.7%, and 18.3% to 56.7% across relevant kernels for three scanners from one manufacturer.

CONCLUSION

Pseudoenhancement is strongly dependent on multidetector CT convolution kernel. Varying this parameter may mitigate this phenomenon, which is independent of volume-averaging effects.

Subtraction Imaging: Applications for Nonvascular Abdominal MRI

OBJECTIVE

In this article we will illustrate the role of subtraction imaging for abdominal MRI applications.

CONCLUSION

Subtraction imaging has multiple applications for imaging the mediastinum, abdomen, and pelvis. Removing any preexisting signal of T1 unenhanced images causes contrast enhancement within a mass to become more conspicuous on subtracted sequences. This is helpful when evaluating a lesion with high signal on unenhanced T1-weighted sequences, where visual detection of enhancement can be difficult on conventional MRI.

Effect of thin overlapping reconstruction on the attenuation of small (< or = 3 cm) renal cysts in the nephrographic phase of MDCT: a phantom study

Objective

To evaluate the effect of thin overlapping reconstruction on the attenuation of small (≤ 3 cm) renal cysts in the nephrographic phase of multidetector CT (MDCT).

Materials and Methods

We scanned a phantom kidney containing spheres of various sizes (10, 20, and 30 mm) using both 4- and 16-channel MDCT scanners, and reconstructed images with various slice thickness (T, mm) and intervals (I, mm). The attenuation increase (AI) was measured for each sphere in 240-HU diluted solution of contrast material and compared with the attenuation in 35-HU solution.

Results

On the 4-channel MDCT, thin overlapping reconstruction (T/I = 3/1, compared with 5/5) lowered the AI as much as 17 HU in the 10 mm-sphere and 6 HU in the 20 mm-sphere (p < 0.05). Thin slicing alone was also effective; however overlapping alone was not. On the 16-channel MDCT, AI in the 10 mm-sphere was significantly lower than on the 4-channel MDCT with T/I = 5/5 (p < 0.05), however thinner slicing or overlapping did not affect the attenuation significantly in all of the spheres.

Conclusion

The effect of thin overlapping reconstruction on minimizing falsely elevated attenuation in the nephrographic phase was significant only in cysts ≤ 20 mm on the 4-channel MDCT.

Multidetector computed tomography urography (MDCTU) for diagnosing urothelial malignancy

Multidetector computed tomography (MDCT) is well established for the detection of stones and renal masses, but more recently MDCT urography (MDCTU) is becoming widely used for examination of the entire urinary tract aimed specifically for diagnosing urothelial lesions. Evidence is rapidly accumulating to support the use of MDCTU in this manner. Familiarity with the MDCTU signs of urothelial malignancy is a prerequisite for optimum radiological practice. This article provides a review of the appearances of transitional cell cancer in the upper urinary tract and bladder.

Imaging of kidney cancer

Advances in molecular genetics have expanded the understanding of renal cell tumors. Now it is understood that renal cortical tumors are a family of neoplasms with distinct cytogenetics and molecular defects, unique histopathologic features, and different malignant potentials. Imaging contributes to clinical management of patients with renal tumors in providing diagnostic information for tumor detection, characterization, staging, treatment planning, and follow-up.

Small hepatic lesions found on single-phase helical CT in patients with malignancy: Diagnostic capability of breath-hold, multisection fluid-attenuated inversion-recovery (FLAIR) MR imaging using a half-fourier acquisition single-shot turbo spin-echo (HASTE) sequence

PURPOSE

To evaluate the diagnostic capability of breath-hold, multisection fluid-attenuated inversion-recovery (FLAIR) imaging using a half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence in combination with T2-weighted fast spin-echo (FSE) magnetic resonance (MR) sequences for small hepatic lesions found on CT in patients with malignancy.

MATERIALS AND METHODS

This study included 48 patients with extrahepatic malignancy who underwent both CT and MR examinations. There were a total of 112 small hepatic lesions (73 cysts and 39 liver metastases, <2 cm in diameter) that showed low attenuation on enhanced CT. Three radiologists independently reviewed the CT and MR (FLAIR-HASTE and T2-weighted FSE) images and assigned a confidence level to their evaluation (cyst or metastasis) on a five-point scale.

RESULTS

All three reviewers were significantly better able (P < 0.05) to differentiate small hepatic cyst from liver metastasis with combined FLAIR-HASTE and T2-weighted FSE images (Az values = 0.997-0.999) than with CT (0.917-0.932). The mean values of sensitivity, specificity, and accuracy were significantly higher (P < 0.001) for T2-weighted FSE with FLAIR-HASTE (96.6%, 96.8%, and 96.7%, respectively) than for CT (76.9%, 61.6%, and 67.3%, respectively). A confident diagnosis was rendered in 12 of 112 lesions (10.7%) on the basis of CT, and this rate increased to 83 of 112 (74.1%) on the basis of T2-weighted FSE and FLAIR-HASTE imaging.

CONCLUSION

FLAIR-HASTE is considered to be an effective sequence for differentiating hepatic cysts from liver metastases without the use of a contrast agent. With FLAIR-HASTE one can confidently diagnose small hepatic lesions found on CT in patients with a malignancy.

Understanding and Interpreting MRI of the Genitourinary Tract

This article familiarizes the urologist with the most common pulse sequences used in MRI to evaluate the kidneys and adrenal glands. It serves as a basis on which interpretation of genitourinary MRI can be facilitated, and includes specifics on how to perform these studies. MRI analysis of renal masses, cysts, and cystic masses is reviewed thoroughly and the critical factor in determining enhancement in renal lesions is detailed. Adrenal imaging for metastatic disease is reviewed. MR urography is also discussed briefly.

Characterization of Small Liver Lesions

OBJECTIVE

The purpose of this study is to evaluate the added role of magnetic resonance imaging (MR) in characterizing subcentimeter focal liver lesion(s) detected on multidetector row helical computed tomography (MDCT).

MATERIALS AND METHODS

A retrospective analysis was performed in 59 noncirrhotic patients with focal subcentimeter liver lesion(s) detected on a 4- or 16-slice MDCT. All patients had a gadolinium enhanced liver MR on 1.5-T systems within 6 weeks after MDCT. Imaging diagnosis was graded on an ordinal scale of 0-5 (0, normal; 1, definitely benign; and 5, definitely malignant). The final diagnosis was established either by histopathology or follow-up imaging for a period of at least 6 months. Receiver operating characteristic analysis was performed to compare the performances of MDCT and MR in characterization of subcentimeter liver lesions.

RESULTS

A total of 178 lesions were detected on MDCT in 59 patients. Of these lesions, 129 (72.5%) lesions were benign and the remaining 49 were malignant. The sensitivity, specificity, positive predictive value, and negative predictive value in differentiation of benign from malignant lesions on MDCT were 81.2%, 77.3%, 60.5%, 90.6 % and on MR were 83.3%, 97.5%, 92.1%, and 94.4 %, respectively. Comparative receiver operating characteristic analysis showed an area under curve for MDCT = 0.76 and MR = 0.95 (P < 0.001).

CONCLUSIONS

Liver MR has significantly higher accuracy for characterization of subcentimeter focal liver lesions discovered on MDCT.

CT Histogram Analysis in Pathologically Proven Adrenal Masses

OBJECTIVE

The purpose of this article is to evaluate a histogram analysis method for distinguishing adrenal adenomas from metastases, pheochromocytomas, and adrenocortical carcinomas on CT.

MATERIALS AND METHODS

A pathology database was searched, and 335 adrenalectomies from 1995 to 2002 were identified. CT images were available for retrospective review in 187 patients (93 males, 94 females; age range, 15-84 years; mean age, 55.2 years) with 208 adrenal masses. This included 112 adenomas in 104 patients, 48 metastases in 39 patients, 40 pheochromocytomas in 36 patients, and eight adrenocortical carcinomas in eight patients. Histogram analysis was performed using a circular region of interest for mean attenuation, number of pixels, number of negative pixels (< 0 H), and percentage of negative pixels by two interpreters. Areas of necrosis were excluded from measurements. Observer agreement was calculated.

RESULTS

In 72 of 76 (94.7%) and 63 of 72 (87.5%) adenomas, respectively, interpreters found attenuation values greater than 10 H contained negative pixels on unenhanced CT scans. None of the enhanced adenomas had mean attenuation less than or equal to 10 H, but 24 (38.7%) and 28 (45.2%), respectively, had negative pixels. Negative pixels were present in unenhanced and enhanced metastases, pheochromocytomas, and carcinomas. Using a 5% or 10% negative pixel threshold value to diagnose adenoma improved specificity but diminished sensitivity. Specificity for a 10% negative pixel threshold was approximately 88% for unenhanced CT scans and 99% for enhanced CT scans, with sensitivities of 71% and 12%, respectively.

CONCLUSION

Although specificity for the diagnosis of adenomas on enhanced CT scans with histogram analysis was high when a 10% negative pixel threshold was used, low sensitivity likely limits clinical usefulness.

The management of indeterminate incidental findings detected at abdominal CT

Abdominal computed tomography (CT) scans often have findings that are incidental to the reason the study was ordered. Several recent studies and reviews have addressed how these findings should be managed. This article summarizes current management strategies for several types of lesions that are commonly encountered. Some of these findings can be characterized without additional imaging (including simple renal cyst, angiomyolipoma, hepatic steatosis). Other findings are indeterminate. While some of these indeterminate incidental findings can be ignored based on statistical arguments (for example, a sharply circumscribed homogeneous low-attenuation renal lesion under 1 cm in patients without a predisposition to develop renal cell carcinoma), many may need additional imaging studies to either characterize them or demonstrate stability over time. Adhering to these strategies will hopefully reduce overutilization of imaging services while directing attention to those findings which need diagnostic or therapeutic interventions.

How I Do It: Evaluating Renal Masses

With modern computed tomography (CT) and magnetic resonance (MR) imaging equipment, the diagnosis of most renal masses is usually straightforward and accurate. The major question to be answered is whether the mass represents a surgical or nonsurgical lesion or, in some cases, if follow-up studies are necessary. This evaluation usually can be accomplished if a high-quality examination is performed, if the clinical history of the patient is kept in mind, if conditions that mimic a renal neoplasm are considered and excluded, and if there is an awareness of the potential pitfalls and limitations of CT and MR imaging. In this article, the authors present their technique in the performance of CT and MR imaging examinations, summarize their approach to the diagnosis of renal masses, review the imaging findings in these lesions, and stress the limitations in renal mass diagnosis.

Small Hypoattenuating Hepatic Lesions at Contrast-enhanced CT: Prognostic Importance in Patients with Breast Cancer

PURPOSE

To retrospectively determine the prognostic importance of small hypoattenuating hepatic lesions at contrast material-enhanced computed tomography (CT) in patients with breast cancer.

MATERIALS AND METHODS

This retrospective study was approved by the committee on human research. Written informed consent was not required. The authors retrospectively identified 153 patients with breast cancer who underwent serial abdominal CT and who did not have definite liver metastases present at initial CT. The mean age was 56 years (age range, 27-93 years). Two readers independently recorded the presence, size, and number of small (15 mm or less in diameter) hypoattenuating hepatic lesions at initial CT. Another reader independently recorded the presence or absence of definite hepatic metastases at final CT. The association between the presence, size, and number of small hypoattenuating hepatic lesions at initial CT and the subsequent development of metastases was analyzed by using Kaplan-Meier analysis.

RESULTS

One or more small hypoattenuating hepatic lesions were seen at initial CT in 54 of 153 patients (35%). After a median follow-up of 584 days (range, 16-1827 days), definite hepatic metastases developed in 43 of 153 patients (28%), including 15 of 54 patients (28%) with hypoattenuating lesions at initial CT and 28 of 99 patients (28%) without hypoattenuating lesions at initial CT. Findings from the Kaplan-Meier analysis showed no association between the presence (P = .56), size (P = .55), or number (P = .30) of small hypoattenuating hepatic lesions at initial CT and the subsequent development of hepatic metastases.

CONCLUSION

In patients with breast cancer who do not have definite hepatic metastases at initial examination, there is no evidence that small hypoattenuating hepatic lesions seen at initial CT contribute to an increased risk of subsequently developing hepatic metastases.

Renal Masses: Quantitative Analysis of Enhancement with Signal Intensity Measurements versus Qualitative Analysis of Enhancement with Image Subtraction for Diagnosing Malignancy at MR Imaging

PURPOSE

To retrospectively compare quantitative and qualitative methods of assessing magnetic resonance (MR) imaging contrast enhancement as the basis for diagnosing renal malignancy.

MATERIALS AND METHODS

MR imaging was performed by using a gadolinium-enhanced breath-hold fat-suppressed three-dimensional T1-weighted gradient-echo sequence in 71 patients (48 men and 23 women; mean age, 62 years; age range, 26-87 years) with 93 renal lesions for which pathologic correlation was available. For quantitative measurements of enhancement, the relative increase in signal intensity values was measured by one investigator with manually defined regions of interest, and the threshold of an increase of 15% or greater was used to distinguish malignant from benign masses. For qualitative assessment, two investigators independently reviewed the subtracted images of all lesions and subjectively determined whether enhancement was present or absent. The sensitivity, specificity, and positive and negative predictive values for each method were calculated and compared. Mean (+/- standard deviation) and median values of relative enhancement were also calculated for benign and malignant lesions.

RESULTS

At pathologic analysis, 74 (80%) of the 93 lesions were malignant, and 19 (20%)-including seven oncocytomas-were benign. For diagnosing malignancy based on enhancement alone, sensitivity and specificity, respectively, were 95% (70 of 74 lesions) and 53% (10 of 19 lesions) at quantitative analysis and 99% (73 of 74 lesions) and 58% (11 of 19 lesions) at qualitative analysis. All seven oncocytomas were considered to be malignant with both methods. When the oncocytomas were excluded, specificities increased to 83% (10 of 12 lesions) and 92% (11 of 12 lesions) for the quantitative and qualitative evaluations, respectively. Three of the four malignant lesions incorrectly characterized as benign at quantitative assessment were hyperintense on unenhanced MR images; all were diagnosed correctly at qualitative evaluation.

CONCLUSION

Image subtraction enables accurate assessment of renal tumor enhancement, particularly in the setting of masses that are hyperintense on unenhanced MR images.

Evaluation of Small (≤ 3 cm) Renal Masses with MDCT:Benefits of Thin Overlapping Reconstructions

OBJECTIVE

Our purpose was to determine whether thin overlapping reconstructions using MDCT improve the detection and characterization of small renal masses.

MATERIALS AND METHODS

Thirty-seven patients were scanned with MDCT using 2.5-mm collimation. Nephrographic phase data were reconstructed in two ways: a standard protocol (5-mm section thickness, no overlap) and an experimental protocol (3-mm section thickness, 50% overlap). Masses were detected and classified into three groups: group 1, measuring less than 20 H on both protocols (classified as cysts on both); group 2, measuring 20 H or greater on standard protocol and less than 20 H on experimental protocol (classified as cysts using experimental protocol only); and group 3, measuring 20 H or greater on both protocols (not classified as cysts using either protocol). Masses 10 mm or larger in group 3 were evaluated further for enhancement. Statistically significant differences between protocols were assessed using an analysis of counts and proportions.

RESULTS

Of 175 detected lesions, 29 (17%) were detected only with the experimental protocol; all but one were smaller than 5 mm. Using the experimental protocol, of 45 masses between 5 and 10 mm, the number of masses that could be characterized as cysts increased from 13 (29%) to 38 (84%). The overall number of indeterminate lesions was reduced from 101 (69%) of 146 lesions detected with the standard protocol to 86 (53%) of 161 lesions detected with the experimental protocol.

CONCLUSION

Using MDCT and thin overlapping reconstructions, renal cysts as small as 5 mm can be diagnosed with more confidence than is possible with standard reconstructions, and the overall number of indeterminate renal masses is reduced.

Multiphasic Helical CT Criteria for Differentiation of Recurrent Neoplasm and Desmoplastic Reaction after Laparoscopic Resection of Renal Mass Lesions

BACKGROUND AND PURPOSE

Differentiation of recurrent neoplasm and desmoplastic reaction following laparoscopic resection of renal mass lesions poses a problem. The usefulness of multiphasic helical CT-generated criteria based on enhancement and morphologic characteristics was investigated.

PATIENTS AND METHODS

The findings in 5 female and 12 male patients aged 29 to 68 years having renal-cell carcinoma (11-38 mm; N = 15) or solitary angiomyolipomas (N = 2) treated by laparoscopic resection (N = 15) or open segmental surgery (N = 2) were analyzed. Multiphasic helical CT was performed in the preenhancement, arterial corticomedullary, parenchymal, and excretory phases generating 2.5- to 7-mm slices.

RESULTS

Both recurrent neoplasms showed median postcontrast enhancement of 119 HU in the arterial corticomedullary phase; the median enhancement of desmoplastic masses was 48 HU. In the parenchymal and excretory phase, recurrent neoplasms showed progressive loss of enhancement, whereas desmoplastic lesions sustained enhancement at about the same level. Recurrent neoplasms presented a defined mass with characteristic spiculation, whereas desmoplastic reaction was characterized by an ill-defined mass with spidery projections extending to abutting fat and residual fascial planes. On 2- to 3-month follow-up scans, recurrent neoplasms showed progressive increases in size and desmoplastic reaction a sharp decrease.

CONCLUSION

Enhancement of the mass at the operative site on arterial corticomedullary-phase CT to >90 HU strongly suggests recurrent renal-cell carcinoma, while progressive decrease in size on 1- to 3-month follow-up CT suggests a desmoplastic reaction.

CT Density Measurements for Characterization of Adrenal Tumors Ex Vivo:Variability Among Three CT Scanners

OBJECTIVE

Many studies have suggested that Hounsfield measurements on unenhanced CT can reliably differentiate adrenal adenomas from nonadenomas using a scanner-independent threshold level. The purpose of this study was to determine whether establishment of a scanner-independent threshold for differentiation of adenomas from nonadenomas is technically feasible.

MATERIALS AND METHODS

Surgically resected adrenal tumor specimens (total, seven; adenomas, three; nonadenomas, four; size range, 17-76 mm), were placed in an anthropomorphic phantom. Lesion specimens were scanned with one MDCT and two single-detector scanners. Scanning protocols for all three scanners included variations in kilovoltage (140, 120, and 80 [Somatom Plus 4, Somatom VolumeZoom] or 100 [Tomoscan AV] kVp) and slice thickness. Hounsfield measurements were performed on exactly matched slices using regions of interest of a constant size.

RESULTS

The difference in lesion Hounsfield measurements among scanning protocols with 140, 120, and 100/80 kVp was up to 6.2 H for the adenoma group and up to 3.8 H for the nonadenoma group. The comparison of the Tomoscan AV and the Somatom Plus 4 scanners showed a mean difference of 2.6 H at 120 kVp and of 4.6 H at 140 kVp. The differences between the Tomoscan AV and Somatom VolumeZoom scanners were 1.7 and 3.6 H for 120 and 140 kVp, respectively. Between the two Somatom scanners, the divergence was 2.9 and 3.3 H for the two kilovoltage settings. Differentiation between adenomas and nonadenomas was better at lower kilovoltage. Slice thickness did not affect the CT density measurements significantly.

CONCLUSION

Significant differences in CT density measurements of adrenal tumors may occur when different CT scanners or imaging protocols are used. The dependence of measurements on scanner type and scanning technique makes the recommendation of a universal, scanner- and protocol-independent threshold problematic.

Analysis of Changes in Attenuation of Proven Renal Cysts on Different Scanning Phases of Triphasic MDCT

OBJECTIVE

The purpose of this study is to document changes in attenuation values on triphasic MDCT of histologically or surgically proven cystic renal lesions.

MATERIALS AND METHODS

A retrospective study of all renal lesions greater than 1 cm that underwent triphasic MDCT was performed in 90 patients before partial nephrectomy. Three reviewers independently measured the mean attenuation of all lesions in three phases (unenhanced, corticomedullary, and parenchymal) in a blinded retrospective fashion. Forty-three lesions identified at CT in 27 patients had pathologic or surgical confirmation as cysts (fluid-filled lesions). Mean change in attenuation between phases was calculated and correlated with size, unenhanced density, and percentage of the lesion exophytic from renal parenchyma. All scans were obtained after 150 mL of nonionic contrast material was injected at 3 mL/sec. Scanning delays were 30-40 sec (corticomedullary phase) and 120 sec (parenchymal phase).

RESULTS

The mean change in attenuation coefficient of the cysts from the unenhanced to the parenchymal phase was -1.8 H (SD, +/- 4.4 H); from the unenhanced to the corticomedullary phase was -2.3 H (+/- 3.9 H); and from the corticomedullary to the parenchymal phase was 0.6 H (+/- 4.2 H). No cyst increased more than 10 H between the unenhanced and the parenchymal phases; more than 95% of cysts increased less than 8 H between any scanning phases. No significant difference was seen in enhancement related to lesion size (p > 0.054), unenhanced attenuation (p > 0.255), or percentage of the lesion that was exophytic (p > 0.124).

CONCLUSION

The attenuation coefficient of a cystic renal lesion increased by no more than 10 H among the unenhanced, corticomedullary, and parenchymal phase scans.

Multi-detector row CT urography in the evaluation of hematuria

Hematuria can be well evaluated with a comprehensive contrast material-enhanced multi-detector row computed tomography (CT) protocol that combines unenhanced, nephrographic-phase, and excretory-phase imaging. Unenhanced images are obtained from the kidneys to the bladder and allow optimal detection of renal calculi, a common cause of hematuria. Renal parenchymal abnormalities, particularly masses, are best visualized on nephrographic-phase images, which also provide excellent evaluation of the other abdominal organs. Thin-section delayed images obtained from the kidneys to the bladder demonstrate the urinary tract distended with contrast material and are useful in detecting urothelial disease. Intravenous urography, ultrasonography, CT, retrograde ureterography and pyelography, cystoscopy, and ureteroscopy can all be used to evaluate patients with hematuria. In the past, a combination of several of these examinations was necessary to fully evaluate these patients. Now, however, this CT protocol may permit evaluation of hematuria patients with a single comprehensive examination, although more experience and data are needed to determine its efficacy in this setting.

Three-dimensional noninvasive contrast-enhanced electron beam tomography angiography of the kidneys

OBJECTIVE

To indicate the use of 3D electron beam computerized tomography angiography (EBCTA) for renal artery lesions, vascular variants that are crucial to detect before surgery, especially partial nephrectomy and extension of the intravascular tumor.

METHODS

Forty patients (30 men, 10 women, age range 13-82, mean age 54.2) underwent EBCT (GE-Imatron, C 150 ultrafast CT scanner) of the renal arteries. It is essential to review the axial images for all necessary information before the 3D technique is performed.

RESULTS

Maximum intensity projection (MIP) and volume rendering (VR) images were excellent in demonstrating stenosis of the renal arteries. Accessory and main renal arteries were easily depicted, and stenosis has been shown. In our study, among 40 renal angiography patients, 21 had stenosis of the renal arteries with different percentages. A total of 12 accessory renal arteries (five left, seven right) were detected. EBCT, with its 3D techniques, was found to be accurate and useful for renal vascular anatomy as a noninvasive test to delineate renal tumors and renal anatomy prior to nephron sparing surgery because it is known to conserve normal renal parenchyma adjacent to tumor.

CONCLUSION

EBCT, with its noninvasive VR and MIP techniques, is easy to apply and is functional and accurate for neoplasms, renal vascular anatomy and renal artery stenosis.

Adrenal masses: CT characterization with histogram analysis method

PURPOSE

To evaluate a histogram analysis method for differentiating adrenal adenoma from metastasis at computed tomography (CT).

MATERIALS AND METHODS

In a retrospective review of 2 years of clinical CT records, 223 adrenal adenomas in 193 patients (115 with contrast material-enhanced CT, 43 with unenhanced and enhanced CT, and 35 with unenhanced CT) and 31 metastases (25 patients with enhanced CT) were found. In 158 patients with adenomas at enhanced CT, diagnosis was based on stable mass size for more than 1 year (n = 135) and characteristic signal intensity decrease at chemical shift magnetic resonance imaging (n = 23). In 35 patients with adenomas at unenhanced CT, mean attenuation was 10 HU or less. Diagnosis of all metastases was based on rapid growth of a mass or new mass in less than 6 months in patients with cancer. Adrenal metastases with extensive necrosis were excluded. Histogram analysis was performed in a circular region of interest (ROI) for mean attenuation, number of pixels, and range of pixel attenuation for all pixels and for the subset of pixels with less than 0 HU ("negative" pixels). Correlation between mean attenuation and percentage negative pixels was calculated.

RESULTS

Negative pixels were present in all 74 unenhanced adenomas with mean attenuation of 10 HU or less and in 14 of 16 unenhanced adenomas with mean attenuation above 10 HU. Of 184 enhanced adenomas, only 20 had mean attenuation of 10 HU or less, but 97 contained negative pixels (77 of these 97 masses had mean attenuation above 10 HU). Increase in percentage negative pixels was highly correlated with decrease in mean attenuation of both unenhanced and enhanced adenomas. None of the adrenal metastases had mean attenuation of 10 HU or less or contained negative pixels.

CONCLUSION

The histogram method is far more sensitive than the 10-HU threshold method for diagnosis of adrenal adenomas at enhanced CT, with specificity maintained at 100%.

MR techniques for renal imaging

This article describes the principles, attributes, and pitfalls of the many MR imaging approaches available for assessment of renal-related disorders. Tables 1 and 2 summarize the specific approach and rationale.

Renal imaging for diagnosis and staging of renal cell carcinoma

The development and expansion of CT and MRI technology have enhanced the detection and characterization of renal lesions. Although these advancements should lead to earlier diagnosis of renal cell carcinoma with subsequent improved cure rates, the increased imaging has also uncovered many cases that are problematic not only in diagnosis but in management as well. The performance of high-quality examinations combined with growing experience should improve the ability to diagnose and manage these cases successfully. Continued advances in CT and MR technology combined with the current trend toward minimally invasive surgery will continue to expand the role of preoperative imaging and, it is hoped, improve the cure rate of renal cancer.

Detection of medullary and papillary necrosis at an early stage by multiphasic helical computerized tomography

PURPOSE

Multiphasic helical computerized tomography (CT) is advocated to identify early manifestations of papillary and medullary necrosis based on decreased enhancement of circumscribed areas in the medullary pyramid. At this stage the devascularizing process can be reversed if causative conditions such as infections or diabetes mellitus are effectively treated.

MATERIALS AND METHODS

Multiphasic helical CTs were performed in 31 male and 26 female patients with complaints of microscopic hematuria (41), macroscopic hematuria (2), bacteriuria (39) and pyuria (9). Pre-enhancement, arterial, early corticomedullary, parenchymal and excretory phase helical CTs generated 1.25 to 5 mm. thick slices. Followup examination included multiphasic helical CT at 1 and 3 months, and excretory urography for some patients at 3 months.

RESULTS

Bacteriuria was identified as the probable cause of medullary and papillary necrosis in 39 patients, of whom 28 were treated with effective antibiotic therapy, resulting in normalization and re-perfusion of the initial lesion in 16, no change in 5 and progressive disease in 7 at 3-month followup. Of 8 lesions not treated with specific antibiotic therapy 4 progressed and 4 remained unchanged.

CONCLUSIONS

Multiphasic helical CT unlike the excretory urogram can identify medullary and papillary necrosis at an early stage when effective treatment of the underlying cause can reverse the process of devascularization and prevent sloughing of medullary tissues.

Imaging for renal tumors

PURPOSE OF REVIEW

The present review summarizes current developments in the imaging of renal tumors.

RECENT FINDINGS

Computed tomography (CT), magnetic resonance imaging, and ultrasound are used for diagnosing, characterizing, and staging renal tumors. Recent advances have been made in many areas, but the most significant changes have occurred in helical CT. The traditional roles for CT and magnetic resonance imaging have been expanded to include the use of three-dimensional CT and magnetic resonance imaging as surgical planning tools. Three-phase CT scans are commonly performed for detection, characterization, and staging of renal lesions, but pelvic CT is probably not needed for preoperative staging. Three-phase CT scans are more sensitive for characterization and for identifying the renal vasculature. Enhancement characteristics on these scans can help to distinguish between different tumor types. Finally, CT urography is a promising alternative to conventional excretory urography, with the potential to simplify the imaging evaluation of patients with hematuria.

SUMMARY

Although ultrasound and magnetic resonance imaging have many indications for imaging renal tumors, CT, with new uses and improved diagnostic capabilities, remains the gold standard in renal imaging.

Renal MDCT

Multidetector CT has expanded the utility of CT by improving longitudinal resolution and acquisition speed. Applications include diagnosis of renal vascular and parenchymal injuries, renal tumor diagnosis and staging, the emerging field of CT urography and CT angiography. This summary review illustrates MDCT approaches to the evaluation of trauma, suspected tumor and imaging of the urinary tract and discusses other applications in renal inflammatory disease, urolithiasis and renal anomalies.

Pseudoenhancement of simulated renal cysts in a phantom using different multidetector CT scanners

OBJECTIVE

We undertook this study to determine whether pseudoenhancement of renal cysts occurs on scans obtained with multidetector CT (MDCT) scanners and whether the effect is influenced by scanning parameters.

MATERIALS AND METHODS

A kidney phantom with varying attenuation was created to simulate different levels of renal parenchymal enhancement (150 and 250 H). Two water-filled cylinders simulating renal cysts-one with a 5-mm diameter and one with a 15-mm diameter-were suspended in the "kidney." After validating the pseudoenhancement effect produced in our phantom model with a single-detector helical CT scanner, we investigated the effect with matrix array and adaptive array MDCT scanners using detector configurations of 1.25 and 2.5 mm and beam pitches of 0.75:1.0 and 1.5:1.0 at an effective reconstructed slice thickness of approximately 3 mm. Three sets of experiments were performed at each setting, and mean cyst density was measured. Data were statistically analyzed using the Student's t test and multiple logistic regression analysis when appropriate.

RESULTS

Although pseudoenhancement was observed with MDCT scanners, the effect was statistically significant only for scans depicting the smaller cyst at a background renal density of 250 H on the matrix array MDCT. Modulation of scanning parameters did not alter these findings. Pseudoenhancement was significantly higher with the matrix array MDCT scanner than with the adaptive array MDCT scanner (p < 0.05).

CONCLUSION

In our phantom model, high levels of renal enhancement produced pseudoenhancement in small renal cysts with different models of MDCT scanners, irrespective of pitch or detector configuration.

Renal cyst pseudoenhancement: evaluation with an anthropomorphic body CT phantom

PURPOSE

To determine the effects of cyst diameter and location (intrarenal, exophytic), renal attenuation, section collimation, and computed tomographic (CT) interscanner variability on renal cyst pseudoenhancement in a phantom model.

MATERIALS AND METHODS

A customized anthropomorphic phantom was designed to accept 40-, 140-, and 240-HU renal inserts containing intrarenal and exophytic 7-, 10-, and 15-mm cysts. Each phantom and insert were scanned with five different helical CT scanners by using 1.0-1.5-mm, 2.50-3.75-mm, 5.0-mm, 7.0-8.0-mm, and 10.0-mm section collimation. Means and SDs of CT number measurements were obtained for each cyst within each variably "enhanced" renal insert. Mixed-model analysis of variance accommodating heteroscedasticity of data was used to assess the effect of scanner type, section collimation, and cyst diameter on cyst attenuation.

RESULTS

Pseudoenhancement (range, 10.3-28.3 HU), observed by using effective section collimation equal to or less than 50% of cyst diameter, occurred in 34 (38%) of 90 intrarenal cyst measurements. Pseudoenhancement was observed with all five CT scanners, though the magnitude of the effect was nonuniform. Significant interactions were noted between renal cyst diameter, background renal attenuation, and CT scanner type in terms of their effects on cyst attenuation. No appreciable pseudoenhancement was observed with exophytic cysts.

CONCLUSION

Pseudoenhancement is maximal when small (< or = 1.5-cm) intrarenal cysts are scanned during maximal levels of renal parenchymal enhancement. The magnitude of this effect varies with scanner type but may be large enough to prevent accurate lesion characterization, despite use of a thin-section helical CT data acquisition technique.

Renal masses: quantitative assessment of enhancement with dynamic MR imaging

PURPOSE

To establish a quantitative magnetic resonance (MR) imaging contrast enhancement criterion for distinguishing cysts from solid renal lesions.

MATERIALS AND METHODS

Regions of interest were measured in 74 patients with renal lesions evaluated by means of dynamic contrast material-enhanced MR imaging with serial breath-hold spoiled gradient-echo acquisitions. Sensitivity for renal tumors and specificity for renal cysts were established by using percentage of enhancement thresholds that varied between 5% and 35%.

RESULTS

The mean percentage of enhancement at MR imaging for the 50 renal cysts was less than 5%; for the 50 renal tumors, it was 97% or higher. With use of a threshold percentage of enhancement of 15% and results obtained between 2 and 4 minutes after administration of contrast material, all malignancies (sensitivity for tumor, 100%) were diagnosed, and there were 6% or fewer false-positive tumor diagnoses. Lower thresholds resulted in unacceptably high false-positive rates (ie, cysts that appeared to enhance-pseudoenhancement), whereas higher threshold values (>20%) resulted in an unacceptably lower sensitivity for tumors.

CONCLUSION

The optimal percentage of enhancement threshold for distinguishing cysts from malignancies with the imaging technique prescribed was 15%, and the optimal timing for measurement was 2-4 minutes after administration of contrast material.

Pseudoenhancement of simple renal cysts: a comparison of single and multidetector helical CT

PURPOSE

The purpose of this work was to compare the extent of pseudoenhancement (artifactual increase in measured attenuation of a simple cyst after contrast medium administration) in a phantom model on single detector and multidetector helical CT scanners.

METHOD

The phantom consisted of four water-filled spheres varying in size from 8 to 28 mm, suspended in an aqueous contrast medium bath. Iodine concentration in the bath was varied: 0, 6, 12, and 24 mg/ml corresponding to attenuation values of 0, +108, +180, and +300 HU. The phantom was scanned on single detector and multidetector helical CT scanners during the same session. Collimation (1, 3, and 5 mm) and pitch (1 and 1.5:1, single detector; 3:1 and 6:1, multidetector) were varied at each concentration. All scans were performed at 140 kVp and 170 mA. The region of interest was measured at the center of each sphere. The effects were analyzed using a linear regression model.

RESULTS

The degree of pseudoenhancement was more pronounced with increasing iodine concentration, decreasing cyst size, and wider collimation (all p = 0.0001). Pseudoenhancement was also more marked on the multidetector than the single detector scanner (p = 0.0001). At physiological levels of renal enhancement, the average pseudoenhancement was +18 HU for the single detector versus +23 HU for the multidetector scanner. Variation in pitch had no effect.

CONCLUSION

Pseudoenhancement is greater on a multidetector than a single detector helical CT scanner and may exceed 20 HU at physiological levels of renal enhancement.

Renal cysts: is attenuation artifactually increased on contrast-enhanced CT images?

PURPOSE

To determine if the attenuation values of simple renal cysts are artifactually increased on contrast material-enhanced, clinically acquired spiral computed tomographic (CT) images.

MATERIALS AND METHODS

Dual-phase renal spiral CT studies (5-mm collimation; pitch, 1.0) were retrospectively analyzed in 24 consecutive patients who had ultrasonographic (US) documentation of simple renal cysts. Forty-eight cysts were identified. The attenuation values of each cyst were measured on nonenhanced, cortical phase, and nephrographic phase images. The size and the location of each cyst in relation to the renal parenchyma were also recorded.

RESULTS

The cysts were 0.6-10.8 cm in diameter (mean, 2.6 cm; SD, 2.0). The mean attenuation change in the cysts from nonenhanced to contrast-enhanced images was statistically significant in a comparison of cortical phase and nephrographic phase images (P: <.01): +1.8 HU (SD, 3.8) for cortical phase and +3. 6 HU (SD, 5.6) for nephrographic phase images. Renal cysts 1.0 cm or smaller showed a higher attenuation increase (mean, +4.0 HU for cortical phase and +11.0 HU for nephrographic phase). None of the renal cysts larger than 1.0 cm demonstrated an increase greater than 10 HU (mean, +1.4 HU for cortical phase and +2.3 HU for nephrographic phase). Intraparenchymal cysts showed higher mean attenuation changes than the exophytic cysts.

CONCLUSION

Attenuation values in the renal cysts increased artifactually on contrast-enhanced images, but this pseudoenhancement was not substantial and was less than 10 HU when the cyst was larger than 1. 0 cm in diameter.

Evaluation of pseudoenhancement of renal cysts during contrast-enhanced CT

OBJECTIVE

The purpose of our study was to evaluate renal cyst pseudoenhancement during helical CT in a phantom model and in patients.

MATERIALS AND METHODS

Iodine baths containing water-filled spheres and cylinders were constructed to simulate cysts in enhancing renal parenchyma. Iodine concentration, cyst size and location, collimation, and peak kilovoltage were varied and cyst attenuation was measured. Data were analyzed with the mixed linear models and Mantel-Haenszel tests. Subsequently, a paired t test compared CT attenuation values before and after contrast material enhancement in 40 patients with 68 renal cysts (radiographic stability >3 months).

RESULTS

The attenuation values of phantom cysts increased when placed in a contrast media bath (p = 0.001). The increase in attenuation values became more pronounced with increasing iodine concentrations, decreasing peak kilovoltage, and smaller sphere sizes. In patients, mean cyst attenuation increased 3.4 +/- 6.2 H after administration of contrast material (p = 0.00002). The attenuation did not increase more than 10 H in any of the 37 cysts larger than 2 cm found in patients. Eight (26%) of the 31 cysts smaller than 2 cm found in patients increased by at least 10 H.

CONCLUSION

In a phantom model, at simulated physiologic levels of renal enhancement, cysts may pseudoenhance by more than 10 H. Similarly, in patients, cysts may also pseudoenhance; however, most pseudoenhancement does not exceed 10 H. In patients, pseudoenhancement of at least 10 H is more likely in cysts smaller than 2 cm.