Renal lesions: controlled comparison between CT and 1.5-T MR imaging with nonenhanced and gadolinium-enhanced fat-suppressed spin-echo and breath-hold FLASH techniques

Radiology Imaging Scans for Early Diagnosis of Kidney Tumors: A Review of Data Analytics-Based Machine Learning and Deep Learning Approaches

Plenty of disease types exist in world communities that can be explained by humans’ lifestyles or the economic, social, genetic, and other factors of the country of residence. Recently, most research has focused on studying common diseases in the population to reduce death risks, take the best procedure for treatment, and enhance the healthcare level of the communities. Kidney Disease is one of the common diseases that have affected our societies. Sectionicularly Kidney Tumors (KT) are the 10th most prevalent tumor for men and women worldwide. Overall, the lifetime likelihood of developing a kidney tumor for males is about 1 in 466 (2.02 percent) and it is around 1 in 80 (1.03 percent) for females. Still, more research is needed on new diagnostic, early, and innovative methods regarding finding an appropriate treatment method for KT. Compared to the tedious and time-consuming traditional diagnosis, automatic detection algorithms of machine learning can save diagnosis time, improve test accuracy, and reduce costs. Previous studies have shown that deep learning can play a role in dealing with complex tasks, diagnosis and segmentation, and classification of Kidney Tumors, one of the most malignant tumors. The goals of this review article on deep learning in radiology imaging are to summarize what has already been accomplished, determine the techniques used by the researchers in previous years in diagnosing Kidney Tumors through medical imaging, and identify some promising future avenues, whether in terms of applications or technological developments, as well as identifying common problems, describing ways to expand the data set, summarizing the knowledge and best practices, and determining remaining challenges and future directions.

A Concise Review of the Multimodality Imaging Features of Renal Cell Carcinoma

The evaluation of renal cell carcinoma (RCC) is routinely performed using the multimodality imaging approach, including ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET). Ultrasonography is the most frequently used imaging modality for the initial diagnosis of renal masses. The modality of choice for the characterization of the renal mass is multiphasic CT. Recent advances in CT technology have led to its widespread use as a powerful tool for preoperative planning, reducing the need for catheter angiography for the evaluation of vascular invasion. CT is also the standard imaging modality for staging and follow-up. MRI serves as a problem-solving tool in selected cases of undefined renal lesions. Newer MRI techniques, such as arterial spin labeling and diffusion-weighted imaging, have the potential to characterize renal lesions without contrast media, but these techniques warrant further investigation. PET may be a useful tool for evaluating patients with suspected metastatic disease, but it has modest sensitivity in the diagnosis and staging of RCC. The newer radiotracers may increase the accuracy of PET for RCC diagnosis and staging. In summary, the main imaging modality used for the characterization, staging, and surveillance of RCC is multiphasic CT. Other imaging modalities, such as MRI and PET, are used for selected indications.

Usefulness of Apparent Diffusion Coefficient of Diffusion-Weighted Imaging for Differential Diagnosis of Primary Solid and Cystic Renal Masses

BACKGROUND

To evaluate the value of diffusion-weighted imaging (DWI) for distinguishing between benign and malignant renal masses.

MATERIAL/METHODS

Seventy-five patients with 75 unilateral renal lesions were included, and 75 normal contralateral kidneys served as controls. The lesions were categorized into four groups as malignant cystic, malignant solid, benign cystic and benign solid. The apparent diffusion coefficients (ADCs) were evaluated for two different b values (b=600 s/mm² and b=1000 s/mm²). Receiving operating characteristic analysis was performed to identify threshold ADCs.

RESULTS

Sensitivity and specificity were 67% and 77% (p=0.003) at the cutoff value of 1.5 for b=600 s/mm², and 79% and 62% (p=0.004) at the cutoff value of 1.99 for b=1000 s/mm² as regards the differentiation between solid benign and malignant renal lesions. Sensitivity and specificity were 78% and 79% (p=0.001) at the cutoff value of 3.1 for b=600 s/mm², and 86% and 61% (p=0.003) at the cutoff value of 2.9 for b=1000 s/mm² as regrads the differentiation between benign and malignant cystic renal lesions.

CONCLUSIONS

DWI can be an effective diagnostic method for distinguishing between benign and malignant renal masses.

Utility of semiquantitative strain elastography for differentiation between benign and malignant solid renal masses

OBJECTIVES

The aim of this study was to determine the role of semiquantitative strain elastography for differentiation of benign and malignant solid renal masses.

METHODS

Seventy-one patients with solid renal masses were prospectively examined with ultrasound elastography after grayscale sonography. Strain elastography was used to compare the stiffness of the renal masses and renal parenchyma. The ratio of strain in a renal mass and nearby renal parenchyma was defined as the strain index value. Mean strain index values for benign masses (n = 29; 24 angiomyolipomas and 5 oncocytomas) and malignant masses (n = 42; 34 renal cell carcinomas, 4 transitional cell carcinomas, 3 metastases, and 1 lymphoma) and mean strain index values for angiomyolipomas and renal cell carcinomas were compared.

RESULTS

There were no significant differences in the mean age of the patients, mean diameter of the masses, and mean probe-mass distance between benign and malignant groups. The mean strain index value ± SD for malignant masses (4.05 ± 2.17) was significantly higher than the value for benign masses (1.43 ± 0.94; P < .05). The mean strain index value for renal cell carcinomas (4.30 ± 2.27) was significantly higher than the value for angiomyolipomas (1.28 ± 1.01; P < .0001).

CONCLUSIONS

Strain elastography may be a useful imaging technique for differentiation between benign and malignant solid renal masses.

Imaging the renal mass: a historical review

A matter of months after Roentgen's landmark discovery in 1895, Roentgen's rays were focused on diseases and disorders of the urinary tract, specifically the kidney. At the dawn of the 20th century, urologists in the United States and around the world quickly recognized that by using a variety of metal stylets and radiopaque contrast agents, such as silver salts, the upper urinary tract, namely the ureter, pelvis, and calyces, could be depicted with radiography. Renal cysts and tumors were diagnosed on the basis of deformities in the kidney. Retrograde pyelography dominated the imaging evaluation of the kidney until the discovery of a safe intravenous method for urinary tract imaging (ie, intravenous pyelography). Pioneers and pathfinders in the field of contrast media development and radiologic procedures helped give radiologists the lead role in the work-up of renal masses, an area where urologists once held forth. The subspecialty of uroradiology was born in the middle of the 20th century. Intravenous urography, nephrotomography, and diagnostic angiography with pharmacologic manipulation followed by cyst or mass puncture and biopsy yielded unrivaled specificity for the diagnosis and staging of benign and malignant renal masses. The advent of cross-sectional and multiplanar imaging and the profound effects they had and continue to have on the discovery and characterization of renal masses has been detailed in the pages of Radiology since the 1920s. Ultrasonography, nuclear imaging, computed tomographic scanning, magnetic resonance imaging, and positron emission tomography each have made a claim to a part of the imaging algorithm of modern uroradiologic practice.

The role of quantitative measurement by acoustic radiation force impulse imaging in differentiating benign renal lesions from malignant renal tumours

PURPOSE

The purpose of this preliminary study was to prospectively evaluate the diagnostic performance of acoustic radiation force impulse (ARFI) imaging for differentiating benign lesions from malignant renal tumours.

MATERIALS AND METHODS

Sixty patients with renal lesions were enrolled in the study; mean patient age was 49.52 ± 20.46 years (range 1-83 years) and patients included 30 men and 30 women. Lesions were categorised as benign (n = 19), malignant (n = 36) and infectious (n = 5) in origin. The shear wave velocities (SWVs) of the tumours and the intact parenchyma were determined by ARFI quantification, and the differences in the SWVs were compared among groups. The final diagnoses were determined via pathologic (n = 33), clinical (n = 13) and imaging findings (n = 14). The SWV values of the renal tumours were analysed according to the final diagnoses.

RESULTS

The mean SWV value of the normal renal parenchyma was significantly different from that of all other lesions (p < 0.01). There was a significant difference between the SWV values of benign renal lesions including haematomas and the malignant renal lesions (p = 0.033). However, the SWV values of the infectious lesions and leiomyoma corresponded well with the malignant lesions. A Receiver operating characteristic (ROC) analysis demonstrated a cut-off value of 2.34 m/s between benign and malignant lesions, while sensitivity and specificity were determined to be 88 and 54 %, respectively.

CONCLUSION

ARFI elastography with ARFI quantification may be useful for differentiating benign renal lesions from malignant renal tumours.

Renal cell carcinoma initially presenting as an arteriovenous malformation: a case presentation and a review of the literature

We describe a case of a patient who presented with hematuria and was diagnosed with a renal arteriovenous malformation (AVM). Transcatheter arterial embolization subsequently was performed on this lesion multiple times. Follow-up imaging demonstrated that the AVM was masking an underlying, rapidly growing renal cell carcinoma (RCC). We describe the pathological and radiographic characteristics of AVMs and RCC. We describe the strengths and weaknesses of computed tomography (CT) and magnetic resonance imaging (MRI) to detect and characterize RCC and AVM. We recommend initial and follow-up MR imaging in patients with an AVM to establish a baseline, monitor treatment response, and survey lesions for underlying and obscured malignancy.

Real-time elastography for distinguishing angiomyolipoma from renal cell carcinoma: preliminary observations

OBJECTIVE

The objective of this study was to determine the diagnostic performance of sonoelastography for differentiating angiomyolipomas from renal cell carcinomas.

SUBJECTS AND METHODS

Twenty-eight angiomyolipomas and 19 renal cell carcinomas were prospectively examined with real-time elastography. Lesions were classified according to four elastographic patterns on the basis of the distribution of the blue area (representing no strain and hardest tissue component). The elasticity patterns and the strain ratios of the angiomyolipomas and renal cell carcinomas were evaluated independently by two observers. Diagnostic performance and interobserver agreement were analyzed.

RESULTS

All angiomyolipomas were classified as having a high-strain elastographic pattern (blue areas in < 50% of lesion, considered type 1 or type 2) by both radiologists, whereas 18 of 19 renal cell carcinomas were classified as having a low-strain elastographic pattern (blue areas in ≥ 50% of lesion, considered type 3 or 4) by both radiologists. The respective mean strain ratios measured by two radiologists were 0.15 ± 0.06 and 0.18 ± 0.09 for the angiomyolipomas and 0.64 ± 0.15 and 0.63 ± 0.19 for the renal cell carcinomas. There were significant differences between the elasticity patterns and strain ratios for angiomyolipomas and renal cell carcinomas (p < 0.001). Interobserver agreement was excellent for elasticity patterns and strain ratios, with a weighted kappa coefficient of 0.96 and an intraclass correlation coefficient score of 0.95.

CONCLUSION

Our results show that real-time elastography may be useful in differentiating angiomyolipomas from renal cell carcinomas, by use of both elasticity patterns and strain ratios.

Renal cell carcinoma: dynamic contrast-enhanced MR imaging for differentiation of tumor subtypes--correlation with pathologic findings

PURPOSE

To retrospectively evaluate whether the enhancement patterns of pathologically proved clear cell, papillary, and chromophobe renal cell carcinomas (RCCs) measured on clinical dynamic contrast agent-enhanced magnetic resonance (MR) images permit accurate diagnosis of RCC subtype.

MATERIALS AND METHODS

This study was Institutional Review Board approved and HIPAA compliant; informed consent was waived. One hundred twelve patients (76 men, 36 women; age range, 25-88 years; mean age, 58.1 years) underwent MR imaging of 113 renal masses (mean diameter, 5.4 cm) with pathologic diagnoses of clear cell (n = 75), papillary (n = 28), or chromophobe (n = 10) RCC. A 1.5-T clinical MR protocol was used before and after (corticomedullary and nephrographic phases) intravenous administration of contrast agent. Region-of-interest measurements within tumor and uninvolved renal cortex were used to calculate percentage signal intensity change and tumor-to-cortex enhancement index. Subtype groups were compared by using linear mixed-effects models. Receiver operating characteristic (ROC) curve analysis was performed for the comparison of clear cell and papillary RCCs.

RESULTS

On both the corticomedullary and nephrographic phase images, clear cell RCCs showed greater signal intensity change (205.6% and 247.1%, respectively) than did papillary RCCs (32.1% and 96.6%, respectively) (P < .001). Chromophobe RCCs showed intermediate change (109.9% and 192.5%, respectively). The tumor-to-cortex enhancement indexes at corticomedullary and nephrographic phases were largest for clear cell RCCs (1.4 and 1.2, respectively), smallest for papillary RCCs (0.2 and 0.4, respectively), and intermediate for chromophobe RCCs (0.6 and 0.8, respectively). Signal intensity changes on corticomedullary phase images were the most effective parameter for distinguishing clear cell and papillary RCC (area under ROC curve, 0.99); a threshold value of 84% permitted distinction with 93% sensitivity and 96% specificity.

CONCLUSION

Clear cell, papillary, and chromophobe RCCs demonstrate different patterns of enhancement on two-time point clinical dynamic contrast-enhanced MR images, allowing their differentiation with high sensitivity and specificity.

Radiologic evaluation of small renal masses (I): pretreatment management

When characterizing a small renal mass (SRM), the main question to be answered is whether the mass represents a surgical or nonsurgical lesion or, in some cases, if followup studies are a reasonable option. Is this a task for a urologist or a radiologist? It is obvious that in the increasing clinical scenario where this decision has to be made, both specialists ought to work together. This paper will focus on the principles, indications, and limitations of ultrasound, CT, and MRI to characterize an SRM in 2008 with a detailed review of relevant literature. Special emphasis has been placed on aspects regarding the bidirectional information between radiologists and urologists needed to achieve the best radiological approach to an SRM.

The accuracy of multidetector computerized tomography for evaluating tumor thrombus in patients with renal cell carcinoma

PURPOSE

New advances in computerized tomography, including multidetector computerized tomography with 3-dimensional reformatting has recently called into question the absolute need for magnetic resonance imaging for evaluating renal cell carcinoma with suspected venous involvement. We assessed the accuracy of multidetector computerized tomography for predicting tumor thrombus and the level of venous involvement in patients with renal cell carcinoma.

MATERIALS AND METHODS

We retrospectively reviewed clinical and pathological features in 41 patients with renal cell carcinoma who underwent staging multidetector computerized tomography before surgery. Multidetector computerized tomography findings regarding the presence and level of tumor thrombus were compared to findings at surgery and at final pathological evaluation. All multidetector computerized tomography studies were read by a single radiologist (EKF) before surgery.

RESULTS

When excluding patients with segmental venous involvement only, the concordance rate between multidetector computerized tomography and pathological findings was 84%. Multidetector computerized tomography accurately predicted the level of tumor thrombus in 26 of 27 patients (96%). Four cases of negative multidetector computerized tomography findings were up staged to renal vein involvement based on pathological findings. All 4 patients had early distal thrombi that did not change operative management.

CONCLUSIONS

Multidetector computerized tomography with 3-dimensional mapping is an effective imaging modality for accurately characterizing the level of venous thrombus in patients with renal cell carcinoma. This modality effectively identified patients with clinically significant venous thrombus. Patients with renal cell carcinoma in whom multidetector computerized tomography fails to detect tumor thrombus are unlikely to have a tumor thrombus found at surgery that would change the surgical approach.

Contrast-enhanced timing robust acquisition order with a preparation of the longitudinal signal component (CENTRA plus) for 3D contrast-enhanced abdominal imaging

PURPOSE

To investigate a new image acquisition method that enables an accurate hepatic arterial phase definition and the visualization of contrast agent uptake processes in abdominal organs like liver, spleen, and pancreas.

MATERIALS AND METHODS

A 3D turbo gradient echo method where a fat suppression prepulse is followed by the acquisition of several profiles was combined with an elliptical centric k-space ordering technique and 3D dynamic elliptical centric keyhole. The new k-space ordering method (CENTRA+) was validated experimentally. In an initial clinical evaluation phase the method was employed in five patients to assess the accuracy of the hepatic arterial phase definition and the visualization of the contrast uptake processes in dynamic scanning in abdominal organs like liver, spleen, and pancreas.

RESULTS

In total, five patients were evaluated using the new k-space order. Our initial results indicate that the new k-space order allows consistent capture of the hepatic arterial phase. In dynamic scanning the extreme short temporal resolution obtained with 3D elliptical centric keyhole enables contrast enhancement to be followed in organs with fast contrast uptake characteristics.

CONCLUSION

The elliptical centric nature of the new image acquisition method effectively allows capture of the contrast enhancement processes with good fat suppression.

Renal masses: characterization with diffusion-weighted MR imaging--a preliminary experience

PURPOSE

To retrospectively assess the usefulness of apparent diffusion coefficients (ADCs) for characterizing renal masses (ie, viable solid tumors, necrotic or cystic tumor areas, and benign cysts).

MATERIALS AND METHODS

The institutional review board waived the requirement for informed consent for this retrospective HIPAA-compliant study. The data of 25 consecutive patients (15 men, 10 women; age range, 39-75 years) who underwent renal magnetic resonance (MR) imaging, including diffusion-weighted imaging, before nephrectomy were included. Renal MR examinations were performed by using transverse T1-weighted dual-echo in-phase and out-of-phase sequences and transverse and coronal T2-weighted single-shot fast spin-echo sequences. Three-dimensional fat-saturated T1-weighted dynamic gadopentetate dimeglumine-enhanced sequences also were performed. Precontrast single-shot spin-echo echo-planar diffusion-weighted images were obtained with b values of 0, 500, and 1000 sec/mm(2) at 1.5 T. Regions of interest were placed on renal lesions to measure the ADC of whole lesions, enhancing viable soft tissue, and nonenhancing necrotic or cystic areas. The T1 signal characteristics of the renal lesions and necrotic or cystic areas were recorded. The Wilcoxon rank sum test was used to compare the median ADC values of the various types of lesions and areas.

RESULTS

Twenty-six renal tumors were found in the 25 patients. Eight patients were found to have 11 benign cysts. Renal tumors had significantly lower ADCs (median, 189.3 x 10(-5) mm(2)/sec; range, [102.0-262.0] x 10(-5) mm(2)/sec) compared with benign cysts (median, 322.8 x 10(-5) mm(2)/sec; range, [217.0-421.0] x 10(-5) mm(2)/sec; P < .001). Solid enhancing tumors had significantly lower ADCs (median, 162.3 x 10(-5) mm(2)/sec; range, [102.0-284.0] x 10(-5) mm(2)/sec) compared with nonenhancing necrotic or cystic regions (median, 247.7 x 10(-5) mm(2)/sec; range, [85.2-310.0] x 10(-5) mm(2)/sec; P = .007) [corrected]. T1 hyperintense lesions had lower ADCs compared with their hypointense counterparts.

CONCLUSION

The T1 signal characteristics of a renal lesion appear to be related to the ADC of the lesion. ADC may be helpful in characterizing and differentiating renal masses.

When should abdominal magnetic resonance imaging be used?

When assessing the use of an imaging study, historically 2 criteria were used, diagnostic accuracy and cost of the study. However, as the awareness of risk for radiation-induced cancer in the general population increases as a direct result of more computed tomography (CT) studies being performed, reevaluation of the approach to imaging studies is necessary. The new imaging paradigm considers patient safety as an important aspect of assessing the role of an imaging modality. The primary goals of the new imaging paradigm should be diagnostic accuracy and patient safety, with the secondary goal being more affordable cost of study. In formulating a plan for when to use body magnetic resonance imaging (MRI), one has to consider all of these criteria and should also consider the question of when CT has unmatched diagnostic accuracy. The advantages of the spatial resolution of CT are mainly realized when there is great contrast between what is being looked for and background tissue; examples include small lung nodules and renal calculi. The greater intrinsic soft tissue contrast resolution and greater sensitivity for the presence or absence of intravenous contrast are appreciated in MRI studies, circumstances in which lesions occur within an organ without altering its exterior contour. This is well-shown for liver lesions. Adding patient safety into the equation, MRI should be indicated in exams in which there is no greater difference in diagnostic accuracy between CT and MRI, in patients with greater concern for radiation safety such as pediatric patients, and in cases of multiple or serial exams.

MR classification of renal masses with pathologic correlation

To perform a feature analysis of malignant renal tumors evaluated with magnetic resonance (MR) imaging and to investigate the correlation between MR imaging features and histopathological findings. MR examinations in 79 malignant renal masses were retrospectively evaluated, and a feature analysis was performed. Each renal mass was assigned to one of eight categories from a proposed MRI classification system. The sensitivity and specificity of the MRI classification system to predict the histologic subtype and nuclear grade was calculated. Subvoxel fat on chemical shift imaging correlated to clear cell type (p < 0.05); sensitivity = 42%, specificity = 100%. Large size, intratumoral necrosis, retroperitoneal vascular collaterals, and renal vein thrombosis predicted high-grade clear cell type (p < 0.05). Small size, peripheral location, low intratumoral SI on T2-weighted images, and low-level enhancement were associated with low-grade papillary carcinomas (p < 0.05). The sensitivity and specificity of the MRI classification system for diagnosing low grade clear cell, high-grade clear cell, all clear cell, all papillary, and transitional carcinomas were 50% and 94%, 93% and 75%, 92% and 83%, 80% and 94%, and 100% and 99%, respectively. The MRI feature analysis and proposed classification system help predict the histological type and nuclear grade of renal masses.

Imaging strategies to reduce the risk of radiation in CT studies, including selective substitution with MRI

"When one admits that nothing is certain one must, I think, also admit that some things are much more nearly certain than others." Bertrand Russell (1872-1970) Computed tomography (CT) is one of the largest contributors to man-made radiation doses in medical populations. CT currently accounts for over 60 million examinations in the United States, and its use continues to grow rapidly. The principal concern regarding radiation exposure is that the subject may develop malignancies. For this systematic review we searched journal publications in MEDLINE (1966-2006) using the terms "CT," "ionizing radiation," "cancer risks," "MRI," and "patient safety." We also searched major reports issued from governmental U.S. and world health-related agencies. Many studies have shown that organ doses associated with routine diagnostic CT scans are similar to the low-dose range of radiation received by atomic-bomb survivors. The FDA estimates that a CT examination with an effective dose of 10 mSv may be associated with an increased chance of developing fatal cancer for approximately one patient in 2000, whereas the BEIR VII lifetime risk model predicts that with the same low-dose radiation, approximately one individual in 1000 will develop cancer. There are uncertainties in the current radiation risk estimates, especially at the lower dose levels encountered in CT. To address what should be done to ensure patient safety, in this review we discuss the "as low as reasonably achievable" (ALARA) principle, and the use of MRI as an alternative to CT.

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.

Perfusion MR Imaging with FAIR True FISP Spin Labeling in Patients with and without Renal Artery Stenosis: Initial Experience

The purpose of this study was to prospectively evaluate an arterial spin-labeling technique, flow-sensitive alternating inversion-recovery (FAIR) true fast imaging with steady-state precession (FISP), for noninvasive quantification of renal perfusion in patients without a history of renal artery stenosis (RAS) and in patients with proved RAS. The study was approved by the local ethics committee, and all participants provided written informed consent. Six patients with hypertension but no history of renal artery disease and 12 patients with RAS underwent FAIR true FISP magnetic resonance (MR) imaging in a whole-body 1.5-T unit. RAS grade and scintigraphic perfusion data served as the reference standards. On the FAIR true FISP perfusion images, severe RAS (>70% luminal narrowing) could be clearly distinguished from no or mild RAS and moderate RAS (< or =70% luminal narrowing) (P < .005). Significant correlations between FAIR perfusion data and stenosis grade (r = -0.76) and between FAIR and single photon emission computed tomographic perfusion values (r = 0.83) were observed. FAIR true FISP was found to be suitable for quantitative perfusion imaging of the kidneys in patients with RAS.

Three-dimensional gadolinium-enhanced magnetic resonance breath-hold FLASH imaging in the diagnosis and staging of renal cell carcinoma

Renal cell carcinoma accounts for 2% of all reported cancers. Its apparent incidence is increasing due to the more widespread use of cross-sectional imaging and as a result, tumours are being detected at an earlier stage. It is hoped that this improvement in early detection will result in a significant increase in survival rates. Radiological diagnosis and staging have a critical role in triaging patients' -treatment. Although computed tomography (CT) and ultrasound are well established in the evaluation of renal cell carcinoma, magnetic resonance (MR) techniques are still rapidly developing. In our institution breath-hold three-dimensional (3D) gadolinium-enhanced fast low-angled single shot (FLASH) spoiled gradient-echo sequence imaging has become an integral part of staging for renal cell carcinoma. In this article, we review our experience of the use of this emerging technique in the diagnosis and staging of renal cancer.

Multidetector computed tomography vs magnetic resonance imaging for defining the upper limit of tumour thrombus in renal cell carcinoma: a study and review

OBJECTIVE

To compare the findings of multidetector computed tomography (CT) with surgical pathology and magnetic resonance imaging (MRI), to determine the accuracy of delineating the superior extent of inferior vena cava (IVC) thrombotic involvement in renal cell cancer (RCC).

PATIENTS AND METHODS

A prospective database was examined of 11 patients (median age 65 years, range 45-77) being assessed for suspected IVC extension of RCC tumour thrombus with both multidetector CT and MRI. All had pathology confirming RCC, and eight of those undergoing surgery had pathological confirmation of tumour thrombus extent. All images were analysed originally, then re-analysed by two independent radiologists, an experienced urologist and a urological trainee unaware of the original reports and other imaging results, with a final determination on tumour thrombus level by consensus.

RESULTS

The multidetector CT results were completely accurate when compared with surgical specimens and were in agreement with MRI on all but one occasion, where MRI determined the renal vein to be clear when it was involved on CT and at surgery, giving MRI an accuracy of seven of eight samples.

CONCLUSIONS

Whilst there were few patients and further studies are needed, multidetector CT was comparable with MRI in determining tumour thrombus level. More importantly, in the eight patients with surgical pathological confirmation, multidetector CT was accurate in all. Ultimately, it may replace MRI as the 'gold standard' for imaging to delineate the upper limit of tumour thrombosis in RCC.

MR evaluation of solid renal masses

After diagnosis of a suspicious renal mass on ultrasound or CT, renal MR imaging typically is ordered to characterize the mass further, stage the mass, or resolve discordant ultrasound and CT results. MR imaging may also be ordered in cases in which ultrasound is poor or in instances in which contrast-enhanced CT may be ill advised.

Exploration de l’appareil urinaire en IRM : développements actuels et perspectives futures

New fast MR imaging sequences obtained with high power gradients allow dynamic analysis of parenchymal enhancement by contrast media in order to improve characterization of masses as well as a functional analysis. Phased - array coils have greatly improved spatial resolution. MR Urography is a new valuable modality to study the collecting system. Numerous acronyms are proposed with a wide range of variations between different machines. But basic principles for sequences are similar. MR can be performed in patients with renal insufficiency, iodine allergy or any other contra-indication to the use of ionizing radiation. MRI of the kidney is becoming a major imaging modality to diagnose diseases of the kidney. It provides in a rather short time a "all-in-one approach" of the pathological process.

Imaging of renal lesions: evaluation of fast MRI and helical CT

The purpose of this study is to compare triphasic helical CT and fast MRI with respect to detection, characterization and staging of suspected renal masses. To achieve this triphasic helical CT (plain, corticonephrographic and tubulonephrographic phase) and MRI with fast T(1) weighted and T(2) weighted sequences were performed in 29 patients with a suspected renal lesion. Image quality, lesion characterization and lesion extent were assessed for both methods in all patients. The acquisition phase for CT and the image sequence for MRI offering the best image quality and best diagnostic information regarding renal parenchyma, renal vessels, detection of enlarged lymph nodes, and other abdominal organs were determined. Histologically confirmed renal cell carcinomas (n=18) were staged based on the Robson classification. Quantitative data were obtained from operator-defined regions of interest (ROIs) in all acquisition phases (CT) and all image sequences (MRI). For most criteria the rating of image quality for helical CT was generally higher as compared with fast MRI. CT and MRI detected all 24 histologically proven masses, while no false positive solid tumour was diagnosed with both imaging modalities. All three acquisition phases in CT and all applied image sequences in MRI were regarded as necessary in order to gain important diagnostic information. Altogether, 12 of 18 renal cell carcinomas (67%) were correctly staged by CT and MRI. Helical CT and fast MRI allow the correct detection and characterization of suspicious renal lesions. Both imaging modalities can be recommended for clinical routine application. Although the correct histological staging of renal cancer remains difficult for both imaging methods, both are excellent in providing the critical staging information needed before surgery. Helical CT offers a significantly shorter acquisition time to cover the entire abdomen.

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.

High-resolution multidetector CT in the preoperative evaluation of patients with renal cell carcinoma

OBJECTIVE

The purpose of our study was to evaluate the accuracy of multidetector CT (MDCT) using a high-resolution protocol in the preoperative assessment of patients with renal cell carcinoma who are possible candidates for nephron-sparing surgery.

MATERIALS AND METHODS

Forty patients with suspected renal cell carcinoma underwent MDCT. Contrast-enhanced acquisitions were obtained during arterial, nephrographic, and urographic phases using a thin-slice protocol. One-millimeter-thick source images were evaluated by two observers on a dedicated workstation for the identification and characterization of the tumor, presence of a pseudocapsule or invasion of perirenal fat, involvement of adrenal glands or surrounding tissues, presence of satellite lesions within Gerota's fascia, infiltration of renal vein and inferior vena cava, involvement of lymph nodes, and presence of distant metastases. Imaging findings were compared with surgical specimens using criteria from the Robson and TNM classification systems.

RESULTS

The presence and size of all lesions were correctly shown in all patients. In evaluating Robson stage I of renal cell carcinoma, we were able to diagnose fat infiltration on 1-mm scans with 96% sensitivity, 93% specificity, and 95% accuracy; the positive and negative predictive values were, respectively, 100% and 93%. One hundred percent accuracy was achieved in staging high-grade lesions.

CONCLUSION

High-resolution MDCT is accurate in the preoperative evaluation of patients with renal cell carcinoma.

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.

Pediatric focal xanthogranulomatous pyelonephritis: dynamic contrast-enhanced MRI findings

Xanthogranulomatous pyelonephritis (XPN) is the result of chronic renal infection. It is very rare in childhood and the focal form, which is said to be more common in children, is often misdiagnosed as a renal tumor. We report a case of a focal XPN in a 14-year-old girl. The true preoperative diagnosis may be very hard in children especially in the focal form but it seems to be possible by the help of dynamic contrast-enhanced MRI.

Recommendations for the outpatient surveillance of renal transplant recipients. American Society of Transplantation

Many complications after renal transplantation can be prevented if they are detected early. Guidelines have been developed for the prevention of diseases in the general population, but there are no comprehensive guidelines for the prevention of diseases and complications after renal transplantation. Therefore, the Clinical Practice Guidelines Committee of the American Society of Transplantation developed these guidelines to help physicians and other health care workers provide optimal care for renal transplant recipients. The guidelines are also intended to indirectly help patients receive the access to care that they need to ensure long-term allograft survival, by attempting to systematically define what that care encompasses. The guidelines are applicable to all adult and pediatric renal transplant recipients, and they cover the outpatient screening for and prevention of diseases and complications that commonly occur after renal transplantation. They do not cover the diagnosis and treatment of diseases and complications after they become manifest, and they do not cover the pretransplant evaluation of renal transplant candidates. The guidelines are comprehensive, but they do not pretend to cover every aspect of care. As much as possible, the guidelines are evidence-based, and each recommendation has been given a subjective grade to indicate the strength of evidence that supports the recommendation. It is hoped that these guidelines will provide a framework for additional discussion and research that will improve the care of renal transplant recipients.

Fast breath-hold T2-weighted MRI of the kidney by means of half-Fourier single-shot turbo spin echo: comparison with high resolution turbo spin echo sequence

PURPOSE

The value of the fast half-Fourier single-shot turbo spin echo (HASTE) sequence in T2-weighted MRI of the kidney was evaluated as a substitute for the conventional turbo spin echo (TSE) sequence.

METHOD

Forty-five patients with suspected abnormalities of the kidney underwent MRI with a 1.5 T system. Breath-hold HASTE and respiratory-triggered TSE sequences were performed. Qualitative and quantitative analyses were performed for comparison of these sequences.

RESULTS

The signal-to-noise ratio (SNR) with HASTE was higher than that with TSE. The lesion-to-kidney contrast-to-noise ratio for solid masses with HASTE was almost equal to that with TSE. For cystic masses, the CNR with HASTE was significantly higher than that with TSE (p < 0.05). Respiratory and chemical shift artifacts were significantly smaller on HASTE than on TSE (p < 0.01). However, the blurring artifact was higher on HASTE than on TSE (p = 0.01).

CONCLUSION

The HASTE sequence generates high contrast images and is free of motion and chemical shift artifacts, with much better time efficacy. The sequence provides comparable diagnostic information to TSE sequences.

Small renal masses: assessment of lesion characterization and vascularity on dynamic contrast-enhanced MR imaging with fat suppression

OBJECTIVE

The aim of our study was to characterize renal lesions equal to or smaller than 3.0 cm using dynamic contrast-enhanced MR imaging with fat suppression by means of quantitative analysis of signal intensity.

MATERIALS AND METHODS

We retrospectively reviewed the MR imaging examinations of 35 patients (20 with renal cell carcinoma, eight with angiomyolipoma, and seven with complicated cysts) who were studied with spin-echo and dynamic fat-suppressed gradient-recalled echo MR sequences, before and after the administration of gadopentetate dimeglumine. Every 30 sec after contrast injection, we measured the lesion percentage of enhancement and the ratio of contrast (lesion-renal cortex signal intensity difference) to noise.

RESULTS

Ten renal cell carcinomas were classified as hypervascular (enhancement greater than that of renal cortex) and 10 as hypovascular. The percentage of enhancement of hypervascular carcinomas was similar to that of renal cortex until 150 sec and greater in the late sequences (180-210 sec, p < 0.01). Hypovascular carcinomas had a lower percentage of enhancement than hypervascular carcinomas (60-210 sec, p < 0.005). Angiomyolipomas, after an early enhancement peak, showed values similar to those of hypovascular carcinomas. Complicated cysts had very low enhancement (p < 0.001). The baseline contrast-to-noise ratio was negative for all lesions (hypointensity with respect to renal cortex). After gadolinium injection, the contrast-to-noise ratio of hypervascular carcinomas rose, becoming positive after 150 sec. Until 60 sec, the contrast-to-noise ratio of hypovascular carcinomas declined slightly, whereas that of angiomyolipomas and cysts fell sharply; then the three curves remained stable (60-210 sec, p < 0.05 for all matches except angiomyolipomas versus cysts).

CONCLUSION

Quantitative analysis of signal intensity variations during dynamic contrast-enhanced MR imaging with fat suppression can be useful in the characterization of small renal lesions.

Contrast-enhanced three-dimensional fast spoiled gradient-echo renal MR imaging: evaluation of vascular and nonvascular disease

Breath-hold contrast material enhanced three-dimensional (3D) fast spoiled gradient-echo (FSPGR) sequences are valuable techniques for evaluation of renal arteries and veins and diagnosis of significant renal arterial stenosis at magnetic resonance (MR) imaging. The excellent spatial and contrast resolution with these techniques, combined with the ability to perform studies in multiple vascular phases, also make them attractive for the diagnosis of a wide range of nonvascular processes that affect the kidneys, including renal infections, renal parenchymal diseases, and renal trauma. Particularly when combined with T1- and T2-weighted MR imaging, the contrast-enhanced techniques are highly effective for characterization of renal masses owing to the ability to portray dynamic contrast enhancement. The ability to display venous structures with contrast-enhanced 3D FSPGR techniques helps staging of renal cell carcinoma. This article presents examples of the wide range of vascular and nonvascular renal diseases that may be effectively imaged with contrast material enhanced 3D FSPGR techniques and illustrates the usefulness of the techniques for renal MR imaging.

Quantification and longitudinal trends of kidney, renal cyst, and renal parenchyma volumes in autosomal dominant polycystic kidney disease

ABSTRACT.: The aims of this study were to assess the accuracy and reproducibility of volumetric determinations of total kidney, renal cyst, and renal parenchymal volumes, using fast electron-beam computerized tomography scanning, and to determine the rate of change of these volumes. Nine patients with autosomal dominant polycystic kidney disease (ADPKD) and serum creatinine < or = 1.3 mg/dl and/or an initial iothalamate clearance > or = to 60 ml/min per 1.73 m(2) were imaged weekly over a 3-wk period (total of 3 times). Approximately 8 yr later, they returned for follow-up studies. The kidney volume estimation technique involved a manual segmentation (perimeter drawing) of the kidneys and a semiautomatic threshold approach, using a histogram analysis of the peak densities of renal parenchyma and renal cysts. At entry, total kidney and renal cyst volumes correlated positively with age, while renal parenchymal volumes and GFR correlated negatively with age. The average coefficient of variation values for the three initial consecutive measurements of total kidney, renal cyst (actual and as a percent of total volume), and renal parenchymal volume were 3.4, 7.2, 5.3, and 5.6%, respectively. During the 8 yr of follow-up, total kidney and renal cyst volumes increased, while renal parenchymal volumes and GFR declined. The rate of increase in total kidney and renal cyst volumes varied markedly from patient to patient. There was a significant correlation between rate of increase in renal cyst volume and the rate of decline in GFR. The patients with an initial urine protein/osmolality ratio >0.13 mg/L per mosmol per kg had a significantly higher increase in renal volume and decline in GFR than those with a lower ratio. In summary, the results of this pilot study suggest that: (1) electron-beam computerized tomography is capable of measuring total kidney, renal cyst, and renal parenchymal volumes reproducibly; (2) total kidney and renal cyst volumes increase, while parenchymal volumes decrease with time; (3) the increase in cyst volume correlates best with the decline in renal function; and (4) renal volumes appear to be good surrogate markers for disease progression in ADPKD.

MR imaging of renal masses interpreted on CT to be suspicious

OBJECTIVE

Prior studies have shown that renal MR contrast enhancement improves the efficacy of mass and proximal vascular evaluation. This study assessed the usefulness of different sequences for characterization of masses that appeared suspicious on CT and for prediction of their potential for malignancy.

SUBJECTS AND METHODS

In a prospective manner 32 patients (age range, 26-78 years: average age, 54 years), each with at least one suspicious mass on CT, were examined with MR imaging. The following sequences were performed: conventional spin-echo with and without fat saturation, fast spin-echo, and dynamic gadopentetate dimeglumine-enhanced infusion using a 1.5-T superconducting magnet. Results were analyzed and compared with pathologic results after resection.

RESULTS

A total of 65 renal masses of average size 2.6 cm (range, 1-10 cm) were detected with dynamic MR imaging. Seventeen of the 65 masses were malignant. Of the 17 malignant masses, three did not enhance on dynamic MR imaging (because of hemorrhage). Sixteen of the 17 malignant masses were heterogeneous on T2-weighted images. Three enhancing masses contained fat and all were angiomyolipomas. Thirty-five of the 65 masses (four with hemorrhage) did not show enhancement, all of which were homogeneous on T2-weighted images and were proven to be cysts. Five masses resulted from infections and had heterogeneous T2 appearance. The remaining masses were three hematomas with hemorrhage, one column of Bertin, and one aneurysm.

CONCLUSION

Renal masses that are interpreted as suspicious on CT may lack MR enhancement because of hemorrhage effects; heterogeneity of their T2 appearance is thus critical in differentiating malignancy from benign disease. Odds-ratio calculations give an adjusted estimate of a 3.36-fold increase (95% confidence interval, 1.8-6.27) in the likelihood of malignancy when masses are heterogeneous on T2-weighted images and a 29-fold increase (95% confidence interval, 3.67-241.8) for predicting malignancy when enhancement is present.

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.

Abdominal MR imaging with a volumetric interpolated breath-hold examination

PURPOSE

To compare a T1-weighted, three-dimensional (3D), gradient-echo (GRE) sequence for magnetic resonance (MR) imaging of the body (volumetric interpolated breath-hold examination, or VIBE) with a two-dimensional (2D) GRE breath-hold equivalent.

MATERIALS AND METHODS

Twenty consecutive patients underwent 1.5-T MR imaging. The examinations included pre- and postcontrast (20 mL gadopentetate dimeglumine) fat-saturated 2D GRE breath-hold imaging and fat-saturated volumetric interpolated breath-hold imaging before, during (arterial phase), and after injection, with thin (2-mm source images) and thick (8-mm reconstruction images) sections. The three images were compared qualitatively and quantitatively (signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]).

RESULTS

Qualitatively, the 2-mm source images had poorer pancreatic edge definition on precontrast images compared with the other two data sets (P < .05). On gadolinium-enhanced images, scores for clarity of pancreatic edge, number of vessels visualized, and arterial ghosting were significantly lower for the postcontrast 2D GRE images. Quantitatively, SNR measurements in the liver, aorta, and renal cortex on pre- and postcontrast images were significantly higher for the 8-mm reconstruction images than for the 2D GRE or 2-mm source images (P < .05). Aorta-to-fat CNR was significantly higher on the 8-mm reconstruction images.

CONCLUSION

Fat-saturated volumetric interpolated breath-hold images have quality comparable to that of conventional fat-saturated 2D GRE images.

Evaluation of a 10-minute comprehensive MR imaging examination of the upper abdomen

PURPOSE

To determine whether a 10-minute magnetic resonance (MR) imaging examination of the upper abdomen provides sufficiently comprehensive information to replace a longer MR protocol.

MATERIALS AND METHODS

Images obtained with selected breathing-independent and breath hold MR sequences, with 2 minutes of total acquisition time and an estimated 10 minutes of total study time, in consecutive MR examinations of the upper abdomen in 72 patients (age range, 23-87 years) were retrospectively reviewed in a blinded fashion by two separate interpreters. Determination was made of major and minor findings, and the two separate retrospective interpretations and the prospective clinical interpretation were correlated by using kappa statistics. Surgical and clinical findings were also correlated with imaging findings.

RESULTS

In 61 patients, all major and minor findings were identical in the original clinical interpretation and the two retrospective readings. In 66 patients, the major findings were identical in these three readings. Close agreement was present between the two separate retrospective readings and the prospective clinical interpretation (kappa = 0.49-1.00).

CONCLUSION

The findings suggest that the diagnostic information provided by a shortened MR imaging protocol that includes breath-hold and breathing-independent sequences is in close agreement with lengthier MR protocols. The advantages of a shortened protocol include increased patient throughput and decreased study cost.

Fast and ultrafast magnetic resonance imaging in renal lesions

Our purpose was to analyze and compare the image quality and contrast-to-noise ratio (CNR) of different fast T1- and T2-weighted sequences with conventional spin-echo sequences in renal MRI. Twenty-three patients with focal renal lesions were examined with a T2-weighted ultrafast turbo spin-echo (UTSE) sequence with and without frequency selective fat suppression (SPIR), a combined gradient-and-spin-echo sequence (GraSE), and a conventional spin-echo sequence (SE). In addition, T1-weighted images were obtained pre- and postcontrast, using a fast spin-echo sequence (TSE) with and without SPIR and the conventional SE sequence. Among the T2-weighted images, the highest CNR and the best image quality were obtained with the UTSE sequence, followed by the fat-suppressed UTSE sequence. GraSE and conventional SE sequences showed a significantly lower CNR and image quality (p < 0.05). The T1-weighted sequences did not show significant differences, in either precontrast or postcontrast measurements. T2-weighted UTSE with and without fat suppression combined excellent image quality and high CNR for imaging and detection of renal lesions. The T1-weighted fast sequences provided no alternative to the gradient-echo or to the conventional SE sequences. The results of this systematic study suggest the use of T2-weighted fast techniques for improved diagnostic accuracy of renal MRI.

MRI evaluation of acute renal trauma

We describe the MR findings in a patient with acute renal injury after blunt abdominal trauma associated with perinephric hematoma and urinoma. Both CT and MR findings are described. Active urine extravasation into a perinephric urinoma is demonstrated by serial post-contrast imaging with CT and MRI showing progressively increased attenuation/signal intensity fluid in communication with the collecting system, commencing 2 minutes after contrast administration.

Radiologic evaluation of small and indeterminant renal masses

A common problem in radiologic and urologic practice today is what to do with the small or indeterminant renal mass. Whether found incidentally or sought after because of patient symptomatology, these lesions present a challenge in diagnosis and management. This article outlines the scope of the problem, illustrates representative lesions, suggests imaging and management strategies culled from personal experience, and provides a review of available literature.

Imaging approach to staging of renal cell carcinoma

Current imaging techniques, especially CT and MR imaging, make accurate preoperative staging of renal cell carcinoma possible. Because surgery provides the only effective therapy and because survival depends on local and distant extent, precise staging is critical for preoperative planning and prognosis. This article reviews the advantages, limitations, accuracy, and pitfalls of each of the imaging approaches to staging renal cell carcinoma, concentrating on CT and MR imaging. This information then is summarized in a suggested overall approach to staging renal cell carcinoma.

Helical and electron beam CT scanning in the evaluation of renal vein involvement in patients with renal cell carcinoma

PURPOSE

The purpose of this study was to assess helical and electron beam CT scanning in the evaluation of renal vein involvement in patients with renal cell carcinoma (RCC).

METHOD

Seventy-three patients with 76 pathologically proven RCC who underwent surgical resection or autopsy were evaluated for the accuracy of helical and electron beam CT scanning in the detection of renal vein tumor thrombus in patients with RCC. Patients were entered into the study only if they were scanned on either electron beam or helical CT scanners with intravenous contrast medium enhancement. The tumors involved the right kidney in 38 cases and the left kidney in 38 cases, with tumor size ranging from 1.5 to 19 cm (mean 7 cm). The pathologic grade of the tumor was Grade I in 21, Grade II in 37, Grade III in 15, and Grade IV, in 3 patients.

RESULTS

The accuracy of preoperative CT evaluation of the renal vein for presence or absence of tumor thrombus was 96%. The negative predictive value was 97% and the positive predictive value was 92%. Sensitivity was 85% with a specificity of 98%. In two cases we were unable to detect small intrarenal venous thrombus, although this was present on a microscopic level and did not affect surgical resection. A single false-positive CT result occurred secondary to unopacified blood flow from a capsular vein into the affected renal vein, resulting in a small flow void on CT.

CONCLUSION

The data show that preoperative staging of the renal vein in the patients with RCC is effectively provided with helical and electron beam CT scanning.

Imaging of angiomyolipomas

In this article we review renal angiomyolipomas (AMLs) from cases in the world literature and 60 cases from our own institution. We also analyze the role and the place of the various imaging techniques in the detection and diagnosis of AMLs. Discussion is focused on the natural history of this benign neoplasm as an isolated form or as a part of the tuberous sclerosis (TS) complex or as part of a third less certain group of multiple AML without stigmata of TS. We also consider the growth patterns and hemorrhagic risks of AML to help define an approach to the current management of this lesion.

Renal metastasis. Detection and characterization on enhanced magnetic resonance imaging using an animal model

RATIONALE AND OBJECTIVES

A new animal model was developed in rabbits (renal metastasis using the VX-2 tumor line), and magnetic resonance (MR) imaging performed before and after intravenous gadoteridol injection to assess lesion conspicuity and characterization.

METHODS

Six New Zealand White rabbits with renal metastases were studied on a 1.5-tesla Siemens Vision MR unit. Iodinated contrast was given intravenously to the rabbits, before implantation, to visualize the kidneys under fluoroscopy. Using a 5/8-inch 25-gauge needle, 0.1 mL of minced, screened VX-2 tumor was injected percutaneously into each kidney at the corticomedullary junction. Animals were studied on day 7 after implantation. Baseline fast low-angle shot (FLASH) T1-weighted and fast spin echo T2-weighted breathhold scans were first obtained. Then, an additional precontrast turbo-FLASH T1-weighted scan was acquired. After these scans, 0.1 mmol/kg gadoteridol (gadolinium HP-D03A; ProHance) was injected intravenously at a rate of 1.5 mL/second. Dynamic breathhold turbo-FLASH T1 images were then obtained at 0, 6, 12, 19, 25, and 31 seconds after injection and at 1, 2, and 10 minutes after injection. The T1 multislice FLASH two-dimensional scan was repeated at 10 minutes after contrast. Imaging results were analyzed by region of interest measurement and correlated with tissue pathology.

RESULTS

On dynamic T1-weighted turbo-FLASH scans, lesion conspicuity, specifically (SI(kidney)-SI(tumor)/noise), increased from 7 +/- 7 signal intensity precontrast to a maximum of 14 +/- 8 at 1 minute after contrast. This increase was statistically significant (P = 0.002). An initial rapid increase in tumor conspicuity occurred within the first 30 seconds after contrast, with the curve flattening thereafter. Lesion conspicuity on the precontrast T2-weighted scans was 9 +/- 10, not statistically different from results with either of the precontrast T1-weighted scan techniques. Using T1-weighted FLASH technique, lesion conspicuity increased from 10 +/- 5 precontrast to 31 +/- 12 postcontrast. As with turbo-FLASH, the improvement in tumor conspicuity after contrast on FLASH scans was statistically significant (P = 0.02). The difference between postcontrast FLASH scans and precontrast T2-weighted scans also was statistically significant, with postcontrast scans superior for lesion conspicuity (P = 0.01). Each tumor was confirmed on pathologic exam.

CONCLUSIONS

This research establishes a model of metastasis to the kidney for use in imaging studies. The conspicuity of a small renal metastasis is shown to be improved on early dynamic imaging, as well as at 10 minutes after intravenous injection of 0.1 mmol/kg gadoteridol. Observation of dynamic signal intensity changes provides additional information regarding lesion characterization, supplementing that from precontrast scans.