Magnetic resonance-guided focused ultrasound (MRgFUS) compared with abdominal hysterectomy for treatment of uterine leiomyomas.

OBJECTIVES: To compare women undergoing magnetic resonance-guided focused ultrasound (MRgFUS) to a group of contemporaneously recruited women undergoing total abdominal hysterectomy. Patient demographics, safety parameters, quality of life outcomes and disability measures are reported. METHODS: One hundred and nine women were recruited in seven centers for MRgFUS treatment and 83 women who underwent abdominal hysterectomy were recruited in seven separate centers to provide contemporaneous assessment of safety. The adverse-event profile and disability parameters were prospectively assessed. Patients were also screened at baseline and at 1, 3 and 6 months using the SF-36 health survey questionnaire. RESULTS: There were no life-threatening adverse events in either group. Overall, the number of significant clinical complications and adverse events was lower in women in the MRgFUS group compared to women undergoing hysterectomy. MRgFUS was associated with significantly faster recovery, including resumption of usual activities. At 6 months of follow-up, there were four (4%) treatment failures in the MRgFUS arm. Regarding SF-36 subscale scores, at 6 months there was improvement in all SF-36 subscales for both treatment groups. However, most of the SF-36 subscale scores were significantly better at this stage in the hysterectomy group than in the MRgFUS group. Women undergoing MRgFUS had steady improvement in all parameters throughout the 6-month follow-up period, despite the fact that they continued to have myomatous uteri and menstruation, which at baseline had given them significant symptomatology. CONCLUSIONS: The results of this study show that MRgFUS treatment of uterine leiomyomas leads to clinical improvement with fewer significant clinical complications and adverse events compared to hysterectomy at 6 months' follow-up.

MR imaging-guided prostate interventional imaging: Ready for a clinical use?

Prostate interventional magnetic resonance imaging (MRI) is now routinely performed in many centers. Its more widespread acceptance is limited by the cost of the use of MRI largely related to the long duration time of the procedures. However, the benefit of a robotic assistance has generated a new interest, because it substantially shortens the procedure time, while improving the accuracy. MRI-guided biopsy is considered as an appealing alternative to transrectal ultrasound (TRUS)-guided fusion biopsy, given the limitations of TRUS-MRI image registration systems. MRI-guided focal treatment also benefits from robotic assistance and from the unique property of MRI, which allows the measurement of the temperature in real-time during tumor ablation. The transrectal and transperineal approaches can be used and the respective indications of each pathway will depend on several factors, including the location of the tumor and the examination time, which will condition the occupation time of the MR room, a major factor influencing the overall cost of MRI-guided procedures. This review addresses the current practice of prostate MRI-guided interventional procedures and potential future applications.

Robot-assisted needle placement in open MRI: system architecture, integration and validation.

In prostate cancer treatment, there is a move toward targeted interventions for biopsy and therapy, which has precipitated the need for precise image-guided methods for needle placement. This paper describes an integrated system for planning and performing percutaneous procedures with robotic assistance under MRI guidance. A graphical planning interface allows the physician to specify the set of desired needle trajectories, based on anatomical structures and lesions observed in the patient's registered pre-operative and pre-procedural MR images, immediately prior to the intervention in an open-bore MRI scanner. All image-space coordinates are automatically computed, and are used to position a needle guide by means of an MRI-compatible robotic manipulator, thus avoiding the limitations of the traditional fixed needle template. Automatic alignment of real-time intra-operative images aids visualization of the needle as it is manually inserted through the guide. Results from in-scanner phantom experiments are provided.

Robot-assisted needle placement in open-MRI: system architecture, integration and validation.

This work describes an integrated system for planning and performing percutaneous procedures-such as prostate biopsy-with robotic assistance under MRI-guidance. The physician interacts with a planning interface in order to specify the set of desired needle trajectories, based on anatomical structures and lesions observed in the patient's MR images. All image-space coordinates are automatically computed, and used to position a needle guide by means of an MRI-compatible robotic manipulator, thus avoiding the limitations of the traditional fixed needle template. Direct control of real-time imaging aids visualization of the needle as it is manually inserted through the guide. Results from in-scanner phantom experiments are provided.

Optimizing target coverage by dosimetric feedback during prostate brachytherapy.

PURPOSE: Postimplant dosimetry of permanent prostate implants shows a loss of coverage compared to the preplan. One contributing factor is needle misplacement. The significance of needle misplacement and the clinical utility of dosimetric feedback were analyzed in the setting of interventional magnetic resonance (IMR) guided prostate brachytherapy. METHODS AND MATERIALS: Information provided by an intraoperative planning system was analyzed for 10 patients. Needle misplacement was measured and the dosimetric consequences calculated. Additional catheters and sources were placed following the insertion of all planned catheters to compensate for nonideal needle placement. RESULTS: Source misplacement ranged from 0.0 to 1.0 cm (median, 0.3 cm). The resulting loss of coverage ranged from 1% to 13%, and the intraoperative dosimetric feedback allowed a recovery of from 0% to 12% coverage. Between 0 and 3 (median, 2) additional needles and from 0 to 10 (median, 8) additional sources were required to restore coverage of the target. Final planned coverage exceeded 94% for all patients. CONCLUSION: The discrepancy between planned and achieved needle placement leads to a loss of dosimetric coverage of the target volume. Dosimetric feedback allows compensation for needle divergence. The technique of real-time dosimetric feedback does not require an IMR system, and could be generalized to ultrasound-guided implants.

A clinical method for real-time dosimetric guidance of transperineal 125I prostate implants using interventional magnetic resonance imaging.

PURPOSE: The clinical utility of an interventional magnetic resonance (IMR)-guided implant technique with real-time dosimetric feedback is presented. METHODS AND MATERIALS: The work was carried out at a IMR unit at Brigham and Women's Hospital. Planning and dosimetric feedback were provided by a software system that provides an interface to the IMR images, anatomy demarcation, template registration, dose calculation engine for planning, and evaluating the implant. Planning during the procedure permits the incorporation of actual needle trajectories in the dose calculations. RESULTS: Fifteen patients were planned in the treatment position. During source placement, actual needle locations were incorporated into the dose calculations. After accounting for the observed needle trajectories of the planned needles, 14 of 15 patients (93%) required additional sources to achieve the desired coverage of the target volume. CONCLUSION: A brachytherapy implant procedure which provides clinically significant advances has been implemented. Specifically, the planning system allows dosimetric validation of the needle placement. This procedure is effective in delivering brachytherapy to the target volume and assuring that the implant is delivered in accordance with the preplan. The dosimetric feedback could be incorporated in ultrasound-guided implants.

A practical method to achieve prostate gland immobilization and target verification for daily treatment.

PURPOSE: A practical method to achieve prostate immobilization and daily target localization for external beam radiation treatment is described. METHODS AND MATERIALS: Ten patients who underwent prostate brachytherapy using permanent radioactive source placement were selected for study. To quantify prostate motion both with and without the presence of a specially designed inflatable intrarectal balloon, the computerized tomography-based coordinates of all intraprostatic radioactive sources were compared over 3 consecutive measurements at 1-min intervals. RESULTS: The placement and inflation of the intrarectal balloon were well tolerated by all patients. The mean (range) displacement of the prostate gland when the intrarectal balloon was present vs. absent was 1.3 (0-2.2) mm vs. 1.8 (0-9.1) mm (p = 0.03) at 2 min respectively. The maximum displacement in any direction (anterior-posterior, superior-inferior, or right-left) when the intrarectal balloon was inflated vs. absent was reduced to < or =1 mm from 4 mm. CONCLUSIONS: Both prostate gland immobilization and target verification are possible using a specially designed inflatable intrarectal balloon. Using this device, the posterior margin necessary on the lateral fields to ensure dosimetric coverage of the entire prostate gland could be safely reduced to 5 mm and treatment could be set up and verified using a lateral portal image.

Identifying the predictors of acute urinary retention following magnetic-resonance-guided prostate brachytherapy.

PURPOSE: Larger prostate gland volumes have been associated with long-term urinary morbidity in prostate interstitial radiation therapy utilizing ultrasound image guidance technique. This study was performed to identify the clinical and technical predictors of acute urinary retention following magnetic-resonance (MR)-guided prostate interstitial brachytherapy. METHODS AND MATERIALS: Fifty patients underwent MR-guided prostate brachytherapy between December 1997 and March 1999. Patient selection was limited to men with stage T1cNXM0 disease, PSA of less than10 ng/mL, biopsy Gleason score not more than 3 + 4, and endorectal coil MR stage T2 disease. Dosimetry plans were developed in the operating room and (125)Iodine sources were implanted using MR real-time guidance. The peripheral zone (PZ) of the prostate gland was defined as the clinical target volume (CTV) and the minimum prescribed dose to the CTV was 137 Gy. The volumes of the PZ, transition zone (TZ), and total prostate gland volume were also determined by MR. Individual source strength ranged from 0.35 to 0.54 microGym(2)/h (NIST 99, median 0.46 microGym(2)/h) and the total implanted activity ranged from 17.0 to 43.1 mCi (median, 28.1 mCi) using 43-120 seeds (median, 79). The seeds were placed using MR-compatible biopsy needles (14-28, median, 19). RESULTS: The ability of clinical (MR defined prostate, PZ, and TZ volumes) and technical (number of catheters, number of seeds implanted, and total activity) factors to predict AUR for 50 men undergoing MR-guided prostate interstitial brachytherapy were evaluated using univariable and logistic regression multivariable analyses. Six men (12%) experienced AUR within 24 h after removal of the Foley catheter subsequent to prostate brachytherapy. The total number of seeds (p = 0.05), MR determined prostate volume (p < 0.01), and the MR-determined TZ volume (p < 0.01) were significant predictors of AUR on univariable analysis. Utilizing a multivariable logistic regression analysis, the TZ volume was the only significant predictor of AUR (p < 0.01). The prostate volume is highly correlated to the TZ volume (Spearman correlation coefficient of 0. 91) and was thus significant in the univariable analysis; however, the prostate volume did not add prognostic value in multivariable analysis. CONCLUSION: Benign prostatic hyperplasia (BPH) resulting in an enlarged TZ volume, is the most important predictor of AUR following MR-guided prostate interstitial radiation therapy. Although AUR was significant (60%) in men with moderate BPH (TZ volume >/= 50 cc), it was also self-limiting.

Real-time magnetic resonance image-guided interstitial brachytherapy in the treatment of select patients with clinically localized prostate cancer.

PURPOSE: This study was performed to establish the dose-localization capability and acute toxicity of a real-time intraoperative magnetic resonance (MR) image-guided approach to prostate brachytherapy in select patients with clinically localized prostate cancer. METHODS AND MATERIALS: Nine patients with 1997 American Joint Commission on Cancer (AJCC) clinical stage T1cNxM0 prostate cancer, prostate-specific antigen (PSA) < 10 ng/ml, biopsy Gleason score not exceeding 3 + 4, and endorectal coil MR stage T2 disease were enrolled into this study. The prescribed minimum peripheral dose was 160 Gy to the clinical target volume (CTV), which was the MR-defined peripheral zone (PZ) of the prostate gland. Using a real-time 0.5 Tesla intraoperative MR imaging unit, 5-mm image planes were obtained throughout the prostate gland. The PZ of the prostate gland, anterior rectal wall, and prostatic urethra were identified on the T2 weighted axial images by an MR radiologist. An optimized treatment plan for catheter insertion was generated intraoperatively. Each catheter containing the 125Iodine sources was placed under real-time MR guidance to ensure that its position in the coronal, sagittal, and axial planes was in agreement with the planned trajectory. Real-time dose- volume histogram analyses were used intraoperatively to optimize the dosimetry. RESULTS: For the 9 study patients, 89-99% (median 94%) of the CTV received a minimum peripheral dose of 160 Gy and > or = 95% of the volume of the prostatic urethra and 42-89% (median 70%) of the volume of the anterior rectal wall received doses that were below the reported tolerance. All patients voided spontaneously within 3 h after discontinuation of the Foley catheter and no patient required more than a limited course (< or = 3 weeks) of oral alpha-1 blockers for postimplant urethritis. CONCLUSIONS: Real-time MR-guided interstitial radiation therapy provided the ability to achieve the planned optimized dose-volume histogram profiles to the CTV and healthy juxtaposed structures intraoperatively, with minimal acute morbidity.

Efficacy of prostate-specific antigen and magnetic resonance imaging in staging stage C adenocarcinoma of the prostate.

OBJECTIVES: The authors compared the two most common presurgical tests now used for the preoperative staging of adenocarcinoma of the prostate, prostate-specific antigen (PSA) and magnetic resonance imaging (MRI). METHODS: One hundred consecutive radical retropubic prostatectomy patients were imaged at 1.5 Tesla before surgery with routine T1-weighted and T2-weighted transaxial images. The images were analyzed by two experienced radiologists for evidence of extracapsular disease. Radiologists rated each gland on a scale of 0 to 100 for the percentage likelihood of extracapsular disease based on its MRI appearance. Receiver operator characteristic (ROC) curves were plotted, and areas were calculated for the two radiologists and the preoperative PSA values. RESULTS: Comparison of the areas of the ROC curves generated from the two radiologists and those from the preoperative PSA values showed no statistical difference. CONCLUSIONS: In this series, radiologic interpretation of body coil MRI studies in those patients chosen for a radical retropubic prostatectomy was no better in staging adenocarcinoma of the prostate than simply using the preoperative PSA values.

The use of dynamic magnetic resonance imaging to evaluate orthotopic continent urinary diversion.

OBJECTIVES: The purpose of this study was to evaluate a dynamic magnetic resonance (MR) examination in patients after radical cystoprostatectomy with a neobladder. METHODS: All 12 subjects were studied with the injection of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) and showed normal renal enhancement patterns and upper urinary tracts, except 1 patient who had mild right hydronephrosis. All neobladders were also visualized with gadolinium and 9 of 11 patients were able to void on command. There was close agreement in all cases with the MR findings and other imaging studies. RESULTS: A static and dynamic Gd-DTPA contrast medium MR did image the entire urinary system, similar to a computed tomographic scan or intravenous urogram. Renal function data, similar to a renal radioisotope scan, was obtained from the Gd-DTPA scans. A dynamic voiding study provided visualization of the lower genitourinary tract similar to a conventional voiding cystourethrogram. CONCLUSIONS: We conclude that this single MR technique may provide information similar to that obtained from multiple standard imaging studies in the postoperative assessment of the radical cystectomy patient with a neobladder. It may be especially helpful in the presence of azotemia or contrast allergy.

Evaluation of erectile function in men with sickle cell disease.

OBJECTIVES: To evaluate and characterize erectile manifestations associated with sickle cell disease using nocturnal penile tumescence testing with polysomnography (NPT/PSG) and magnetic resonance imaging (MRI) of the penis. METHODS: Six variably potent men with sickle cell disease, of whom 5 reported a history of priapism, underwent comprehensive evaluations of erectile function. Evaluations involved a medical history and physical examination with completion of priapism and sexual function questionnaires, followed by NPT/PSG and MRI of the penis. RESULTS: Many different erectile abnormalities were identified in this group using NPT/PSG, although nocturnal erection durations as well as detumescence times were uniformly prolonged. Various axial rigidity measurements were obtained, which correlated fairly well with individual reports of erectile function. MRI findings ranged from normal corporeal anatomy to corporeal destruction with intracorporeal fibrosis and hemosiderin deposition. CONCLUSIONS: In sickle cell disease, the erectile dysfunction that commonly occurs may be markedly different among men with this disease and may not always be predicted on the basis of clinical history of priapism. Generally, clinical assessments of erectile function may be derived from clinical histories and physical examinations. NPT/PSG and MRI of the penis are in accord with these assessments, obviating their routine use, although they may be valuable management adjuncts in certain situations.

Assessment of prostate cancer volume using endorectal coil magnetic resonance imaging: a new predictor of tumor response to neoadjuvant androgen suppression therapy.

OBJECTIVES: A clinical tool that can reliably assess prostate cancer response to androgen suppression is lacking. This pilot study was designed to identify the potential clinical factor(s) that correlate with tumor response after neoadjuvant therapy. METHODS: Twenty-one patients managed with definitive local therapy and neoadjuvant androgen suppression (median 3 months [range 2 to 7]) between 1995 and 1997 comprise the study population. Fisher's exact test was used to test the significance of the proportion of patients with a given clinical factor and the outcome of pathologic organ-confined disease. The clinical factors tested included preoperative prostate-specific antigen, biopsy Gleason score, clinical stage, months of total androgen suppression, the change in the endorectal magnetic resonance imaging (erMRI)-defined stage, the change in erMRI-defined tumor, and the change in the erMRI-defined prostate volume during neoadjuvant androgen suppression. RESULTS: All 21 patients had a decrease in the erMRI-determined prostate volume and prostate-specific antigen during androgen suppression, whereas only 10 of 21 (48%) had a reduction in the erMRI-determined tumor volume. There was a statistically significant increased proportion of patients with a decrease in the erMRI-determined tumor volume (P = 0.008) who had pathologic organ-confined disease. CONCLUSIONS: The results of this pilot study suggest that the changes in the erMRI-determined tumor volume occurring during androgen suppression may be predictive of the tumor response. Validation in a larger prospective study is currently underway.

An analysis of the time course of postoperative prostate-specific antigen failure in patients with positive surgical margins: implications on the use of adjuvant therapy.

OBJECTIVES: The role of adjuvant therapy in the postprostatectomy setting for positive margin patients is an unresolved issue. The purpose of this study is to provide the rationale for patient selection in Phase III trials that test the impact of adjuvant therapy on survival in positive margin prostate cancer patients. METHODS: Early (12 months or less) and delayed (more than 12 months) postoperative prostate-specific antigen (PSA) failure have been correlated with distant and local failure, respectively, as the site of first failure. In this study, a Cox regression multivariate analysis was used to determine the significant independent clinical and pathologic predictors of early and delayed postoperative PSA failure in 143 margin-positive prostate cancer patients. RESULTS: Margin-positive patients with positive pelvic lymph nodes, seminal vesicle invasion, or prostatectomy Gleason sum 8 or higher were excluded. For the remaining patients, a prostatectomy Gleason sum of 7, preoperative PSA more than 20 ng/mL, and an endorectal coil magnetic resonance imaging (erMRI) scan showing extensive disease were significant independent predictors of early postoperative PSA failure. Conversely, a prostatectomy Gleason sum of 6 or less, preoperative PSA 20 ng/mL or less, and an erMRI showing limited disease predicted delayed PSA failure. CONCLUSIONS: Preliminary data suggest that the pattern of first failure can be predicted by the time course of rise in the postoperative PSA. The preliminary results of this study suggest that patient selection for clinical trials examining the efficacy of postoperative adjuvant therapy in the positive margin patient may be determined on the basis of the clinical and pathologic characteristics that predict early versus delayed postoperative PSA failure.

Open-configuration MR imaging, intervention, and surgery of the urinary tract.

The open-configuration MR imaging system provides new applications both in diagnosis and in therapy of conditions in the urinary tract. In addition to conventional imaging, the open configuration permits MR imaging of patients in many positions. This has already been shown to be useful in imaging the pelvis during voiding, where a sitting position allows urodynamic evaluation. The lithotomy position can be used for imaging the prostate, which also permits procedural access. The ultimate purpose of the interventional MR imaging suite is to integrate therapeutic tools and techniques with MR imaging. From surgical planning through specialized imaging systems with minimally invasive surgical applications, new methods are being developed and implemented. This new field of image-guided therapy will require extensive clinical development and evaluation for applications in the urinary tract. This will require a large concentrated interdisciplinary effort of surgeons, radiologists, computer scientists, engineers, and physicists. Successful integration of basic research and clinical work will result in a number of cutting-edge technologies with direct clinical application in the urinary tract. Initial projects have included biopsies, endoscopies, and real-time procedural control of high-temperature and cryogenic ablations. It is anticipated that the current surge in image-guided interventions will motivate even more research activity in this field, and will ultimately define the role of MR imaging guidance in urologic intervention and surgery.

Evaluation of three-dimensional finite element-based deformable registration of pre- and intraoperative prostate imaging.

In this report we evaluate an image registration technique that can improve the information content of intraoperative image data by deformable matching of preoperative images. In this study, pretreatment 1.5 tesla (T) magnetic resonance (MR) images of the prostate are registered with 0.5 T intraoperative images. The method involves rigid and nonrigid registration using biomechanical finite element modeling. Preoperative 1.5 T MR imaging is conducted with the patient supine, using an endorectal coil, while intraoperatively, the patient is in the lithotomy position with a rectal obturator in place. We have previously observed that these changes in patient position and rectal filling produce a shape change in the prostate. The registration of 1.5 T preoperative images depicting the prostate substructure [namely central gland (CG) and peripheral zone (PZ)] to 0.5 T intraoperative MR images using this method can facilitate the segmentation of the substructure of the gland for radiation treatment planning. After creating and validating a dataset of manually segmented glands from images obtained in ten sequential MR-guided brachytherapy cases, we conducted a set of experiments to assess our hypothesis that the proposed registration system can significantly improve the quality of matching of the total gland (TG), CG, and PZ. The results showed that the method statistically-significantly improves the quality of match (compared to rigid registration), raising the Dice similarity coefficient (DSC) from prematched coefficients of 0.81, 0.78, and 0.59 for TG, CG, and PZ, respectively, to 0.94, 0.86, and 0.76. A point-based measure of registration agreement was also improved by the deformable registration. CG and PZ volumes are not changed by the registration, indicating that the method maintains the biomechanical topology of the prostate. Although this strategy was tested for MRI-guided brachytherapy, the preliminary results from these experiments suggest that it may be applied to other settings such as transrectal ultrasound-guided therapy, where the integration of preoperative MRI may have a significant impact upon treatment planning and guidance.

Clinical magnetic resonance imaging of the vascular system.

Magnetic resonance imaging is extremely well suited to the diagnostic evaluation of the cardiovascular system. Over the past few years, more effective pulse sequences for imaging the heart and blood vessels have been developed, and although clinical use of cardiac MRI remains limited the use of MR angiographic techniques to evaluate major blood vessels is one of the fastest growing clinical applications of MRI today. The article reviews the current indications for vascular MRI with emphasis on those that are increasingly accepted by referring clinicians.

Mass-like hepatic hypertrophy: MRI findings with histologic correlation.

Hepatic parenchyma may hypertrophy following asymmetrical injury. The histologic characteristics of hypertrophic hepatic parenchyma are more similar to normal hepatic parenchyma than is the more severely damaged liver. We present four cases where large hypertrophic masses resembled neoplasm on other imaging modalities or at surgery, but had MRI signal characteristics similar to those of normal liver.

Bayesian regression methodology for estimating a receiver operating characteristic curve with two radiologic applications: prostate biopsy and spiral CT of ureteral stones.

RATIONALE AND OBJECTIVES: The authors evaluated two Bayesian regression models for receiver operating characteristic (ROC) curve analysis of continuous diagnostic outcome data with covariates. MATERIALS AND METHODS: Full and partial Bayesian regression models were applied to data from two studies (n = 180 and 100, respectively): (a) The diagnostic value of prostate-specific antigen (PSA) levels (outcome variable) for predicting disease after radical prostatectomy (gold standard) was evaluated for three risk groups (covariates) based on Gleason scores. (b) Spiral computed tomography was performed on patients with proved obstructing ureteral stones. The predictive value of stone size (outcome) was evaluated along with two treatment options (gold standard), as well as stone location (in or not in the ureterovesical junction [UVJ]) and patient age (covariates). Summary ROC measures were reported, and various prior distributions of the regression coefficients were investigated. RESULTS: (a) In the PSA example, the ROC areas under the full model were 0.667, 0.769, and 0.703, respectively, for the low-, intermediate-, and high-risk groups. Under the partial model, the area beneath the ROC curve was 0.706. (b) The ROC areas for patients with ureteral stones in the UVJ decreased dramatically with age but otherwise were close to that under the partial model (ie, 0.774). The prior distribution had greater influence in the second example. CONCLUSION: The diagnostic tests were accurate in both examples. PSA levels were most accurate for staging prostate cancer among intermediate-risk patients. Stone size was predictive of treatment option for all patients other than those 40 years or older and with a stone in the UVJ.

Original smooth receiver operating characteristic curve estimation from continuous data: statistical methods for analyzing the predictive value of spiral CT of ureteral stones.

RATIONALE AND OBJECTIVES: Diagnostic studies such as spiral computed tomography (CT) in patients with obstructing ureteral calculi often necessitate the analysis of continuous test data (e.g., stone sizes). The accuracy of a test can be summarized by using a receiver operating characteristic (ROC) curve. The authors developed and compared three methods for constructing a smooth ROC curve from continuous diagnostic data. MATERIALS AND METHODS: Nonparametric, semiparametric, and parametric smooth ROC curve analyses were applied to data from 100 unenhanced spiral CT scans of patients with proved obstructing ureteral stones. Accuracy in using stone size to predict the need for intervention was evaluated by means of these methods. Characteristics and summary measures of the resulting ROC curves were estimated. RESULTS: All methods fit the data well. The nonparametric method followed the details of the empiric data. The semiparametric and parametric methods yielded similar estimates of the ROC curve parameters. Areas under the ROC curves were 0.807, 0.821, and 0.814 for nonparametric, semiparametric, and parametric methods, respectively, in comparison with 0.811 for the empiric method. CONCLUSION: The parametric method is preferred for constructing a smooth ROC curve with available stone-size data derived from spiral CT. The analyses confirm the predictive value of stone size in determining the need for intervention.