CT Detectability of Small Low-Contrast Hypoattenuating Focal Lesions: Iterative Reconstructions versus Filtered Back Projection.

Purpose To investigate performance in detectability of small (≤1 cm) low-contrast hypoattenuating focal lesions by using filtered back projection (FBP) and iterative reconstruction (IR) algorithms from two major CT vendors across a range of 11 radiation exposures. Materials and Methods A low-contrast detectability phantom consisting of 21 low-contrast hypoattenuating focal objects (seven sizes between 2.4 and 10.0 mm, three contrast levels) embedded into a liver-equivalent background was scanned at 11 radiation exposures (volume CT dose index range, 0.5-18.0 mGy; size-specific dose estimate [SSDE] range, 0.8-30.6 mGy) with four high-end CT platforms. Data sets were reconstructed by using FBP and varied strengths of image-based, model-based, and hybrid IRs. Sixteen observers evaluated all data sets for lesion detectability by using a two-alternative-forced-choice (2AFC) paradigm. Diagnostic performances were evaluated by calculating area under the receiver operating characteristic curve (AUC) and by performing noninferiority analyses. Results At benchmark exposure, FBP yielded a mean AUC of 0.79 ± 0.09 (standard deviation) across all platforms which, on average, was approximately 2% lower than that observed with the different IR algorithms, which showed an average AUC of 0.81 ± 0.09 (P = .12). Radiation decreases of 30%, 50%, and 80% resulted in similar declines of observer detectability with FBP (mean AUC decrease, -0.02 ± 0.05, -0.03 ± 0.05, and -0.05 ± 0.05, respectively) and all IR methods investigated (mean AUC decrease, -0.00 ± 0.05, -0.04 ± 0.05, and -0.04 ± 0.05, respectively). For each radiation level and CT platform, variance in performance across observers was greater than that across reconstruction algorithms (P = .03). Conclusion Iterative reconstruction algorithms have limited radiation optimization potential in detectability of small low-contrast hypoattenuating focal lesions. This task may be further complicated by a high degree of variation in radiologists' performances, seemingly exceeding real performance differences among reconstruction algorithms. © RSNA, 2018 Online supplemental material is available for this article.

Repeatability of 18F-FDG uptake in metastatic bone lesions of breast cancer patients and implications for accrual to clinical trials.

BACKGROUND: Standard measures of response such as Response Evaluation Criteria in Solid Tumors are ineffective for bone lesions, often making breast cancer patients that have bone-dominant metastases ineligible for clinical trials with potentially helpful therapies. In this study we prospectively evaluated the test-retest uptake variability of 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG) in a cohort of breast cancer patients with bone-dominant metastases to determine response criteria. The thresholds for 95% specificity of change versus no-change were then applied to a second cohort of breast cancer patients with bone-dominant metastases. METHODS: For this study, nine patients with 38 bone lesions were imaged with 18F-FDG in the same calibrated scanner twice within 14 days. Tumor uptake was quantified by the most commonly used PET parameter, the maximum tumor voxel normalized by dose and body weight (SUVmax) and also by the mean of a 1-cc maximal uptake volume normalized by dose and lean-body-mass (SULpeak). The asymmetric repeatability coefficients with confidence intervals for SUVmax and SULpeak were used to determine the limits of 18F-FDG uptake variability. A second cohort of 28 breast cancer patients with bone-dominant metastases that had 146 metastatic bone lesions was imaged with 18F-FDG before and after standard-of-care therapy for response assessment. RESULTS: The mean relative difference of SUVmax and SULpeak in 38 bone tumors of the first cohort were 4.3% and 6.7%. The upper and lower asymmetric limits of the repeatability coefficient were 19.4% and - 16.3% for SUVmax, and 21.2% and - 17.5% for SULpeak. 18F-FDG repeatability coefficient confidence intervals resulted in the following patient stratification using SULpeak for the second patient cohort: 11-progressive disease, 5-stable disease, 7-partial response, and 1-complete response with three inevaluable patients. The asymmetric repeatability coefficients response criteria for SULpeak changed the status of 3 patients compared to the standard Positron Emission Tomography Response Criteria in Solid Tumors of ± 30% SULpeak. CONCLUSION: In evaluating bone tumor response for breast cancer patients with bone-dominant metastases using 18F-FDG SUVmax, the repeatability coefficients from test-retest studies show that reductions of more than 17% and increases of more than 20% are unlikely to be due to measurement variability. Serial 18F-FDG imaging in clinical trials investigating bone lesions in these patients, such as the ECOG-ACRIN EA1183 trial, benefit from confidence limits that allow interpretation of response.

Repeatability of 18F-FDG uptake in metastatic bone lesions of breast cancer patients and implications for accrual to clinical trials.

BACKGROUND: Standard measures of response such as Response Evaluation Criteria in Solid Tumors are ineffective for bone lesions, often making breast cancer patients with bone-dominant metastases ineligible for clinical trials with potentially helpful therapies. In this study we prospectively evaluated the test-retest uptake variability of 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG) in a cohort of breast cancer patients with bone-dominant metastases to determine response criteria. The thresholds for 95% specificity of change versus no-change were then applied to a second cohort of breast cancer patients with bone-dominant metastases.In this study, nine patients with 38 bone lesions were imaged with 18F-FDG in the same calibrated scanner twice within 14 days. Tumor uptake was quantified as the maximum tumor voxel normalized by dose and body weight (SUVmax) and the mean of a 1-cc maximal uptake volume normalized by dose and lean-body-mass (SULpeak). The asymmetric repeatability coefficients with confidence intervals of SUVmax and SULpeak were used to determine limits of 18F-FDG uptake variability. A second cohort of 28 breast cancer patients with bone-dominant metastases that had 146 metastatic bone lesions was imaged with 18F-FDG before and after standard-of-care therapy for response assessment. RESULTS: The mean relative difference of SUVmax in 38 bone tumors of the first cohort was 4.3%. The upper and lower asymmetric limits of the repeatability coefficient were 19.4% and -16.3%, respectively. The 18F-FDG repeatability coefficient confidence intervals resulted in the following patient stratification for the second patient cohort: 11-progressive disease, 5-stable disease, 7-partial response, and 1-complete response with three inevaluable patients. The asymmetric repeatability coefficients response criteria changed the status of 3 patients compared to standard the standard Positron Emission Tomography Response Criteria in Solid Tumors of ±30% SULpeak. CONCLUSIONS: In evaluating bone tumor response for breast cancer patients with bone-dominant metastases using 18F-FDG uptake, the repeatability coefficients from test-retest studies show that reductions of more than 17% and increases of more than 20% are unlikely to be due to measurement variability. Serial 18F-FDG imaging in clinical trials investigating bone lesions from these patients, such as the ECOG-ACRIN EA1183 trial, benefit from confidence limits that allow interpretation of response.

Imaging of postpartum complications: a multimodality review.

OBJECTIVE: The purpose of this article is to review common and uncommon complications of postpartum and posttermination patients and their imaging findings. A variety of imaging modalities, including ultrasound, CT, MRI, and angiography, will be presented. Knowledge of the spectrum of normal and abnormal imaging findings as well as recognition of the common and uncommon complications are essential for accurate diagnosis. CONCLUSION: Obstetric complications are a common source of morbidity and mortality for women of reproductive age. Imaging, particularly with ultrasound, is often supplementary to the clinical history and examination in assessing and treating women during the postpartum period. Radiologists should be familiar with the common abnormalities that present in this period and their imaging findings, as well as the wide range of normal appearances the postpartum uterus can assume.

How to choose an abdominal imaging fellowship.

Radiologists in training draw from their early experiences in residency when choosing a fellowship. Once they have decided on an abdominal imaging fellowship, applicants must learn to navigate the interview process. During this challenging time, applicants explore the difference in clinical curricula and rotations, meet potential mentors and clinical faculty, consider potential academic interests and projects, and choose what location they would like to train for one year after residency. When in training, fellows undergo the challenge of finding employment while learning new skills and refining their abilities to become a well-rounded radiologist and clinician. This article summarizes key points potential applicants should consider when deciding on an abdominal imaging fellowship, how to prepare for the interview season, and how to plan their fellowship year before fellows take the next step to becoming attendings.

Multimodality Radiological Pictorial Review of Testicular Carcinoma: From Initial Staging to Restaging.

With an overall 5-year survival rate >95%, patients with testicular cancer have a great prognosis. Although initial diagnosis is based on clinical examination, imaging does play a significant role in the diagnosis and prognosis of testicular cancer, which are dependent on tumor burden and staging. Successful treatment requires appropriate disease assessment throughout a patient's treatment: evaluating treatment response, restaging, and monitoring for disease recurrence after treatment completion. Ultrasound is usually the initial screening modality for painless testicular masses, and computedtomography (CT) the most commonly used for staging and restaging. However, with regard to seminomas, positron-emission tomography (PET) combined with CT is slowly taking priority. With regard to nonseminomatous germ-cell tumors, PET-CT has not proven to be completely effective, due to a high number of false-negative results. The purpose of this paper is to provide radiologists with a pictorial review of testicular carcinoma from initial staging through posttreatment follow-up.

The role of radiotracer imaging in the diagnosis and management of patients with breast cancer: part 1--overview, detection, and staging.

Breast cancer is the most common non-skin type of cancer and the second leading cause of cancer mortality in women. Advances in diagnosis and treatment have led to declines in mortality, despite an increase in breast cancer incidence. An advancing array of both local and systemic therapy options has led to increasingly individualized treatment. Imaging plays a key role in detecting breast cancer and directing its therapy. This continuing education article, part 1 in a 2-part series, provides a comprehensive review of current and future radiotracer imaging methods applied to breast cancer, in the context of breast cancer management strategies and other nonnuclear imaging methods. Part 1 of the review provides an overview of clinical and biologic considerations in breast cancer and covers radionuclide imaging for detection and staging. Part 2 will cover radionuclide imaging of breast cancer response to therapy, other clinical indications for radionuclide breast cancer imaging, and future directions, including molecular imaging.

The role of radiotracer imaging in the diagnosis and management of patients with breast cancer: part 2--response to therapy, other indications, and future directions.

Breast cancer is the most common non-skin type of cancer and the second leading cause of cancer mortality in women. Advances in diagnosis and treatment have led to declines in mortality, despite an increase in breast cancer incidence. An advancing array of both local and systemic therapy options has led to increasingly individualized treatment. Imaging plays a key role in detecting breast cancer and directing its therapy. This continuing education article provides a comprehensive review of current and future radiotracer imaging methods applied to breast cancer, in the context of breast cancer management strategies and other nonnuclear imaging methods. Part 1 of the review provided an overview of clinical and biologic considerations in breast cancer and covered radionuclide imaging for detection and staging. Part 2 covers radionuclide imaging of breast cancer response to therapy, other clinical indications for radionuclide breast cancer imaging, and future directions, including molecular imaging.

Test-Retest Reproducibility of 18F-FDG PET/CT Uptake in Cancer Patients Within a Qualified and Calibrated Local Network.

Calibration and reproducibility of quantitative 18F-FDG PET measures are essential for adopting integral 18F-FDG PET/CT biomarkers and response measures in multicenter clinical trials. We implemented a multicenter qualification process using National Institute of Standards and Technology-traceable reference sources for scanners and dose calibrators, and similar patient and imaging protocols. We then assessed SUV in patient test-retest studies. Methods: Five 18F-FDG PET/CT scanners from 4 institutions (2 in a National Cancer Institute-designated Comprehensive Cancer Center, 3 in a community-based network) were qualified for study use. Patients were scanned twice within 15 d, on the same scanner (n = 10); different but same model scanners within an institution (n = 2); or different model scanners at different institutions (n = 11). SUVmax was recorded for lesions, and SUVmean for normal liver uptake. Linear mixed models with random intercept were fitted to evaluate test-retest differences in multiple lesions per patient and to estimate the concordance correlation coefficient. Bland-Altman plots and repeatability coefficients were also produced. Results: In total, 162 lesions (82 bone, 80 soft tissue) were assessed in patients with breast cancer (n = 17) or other cancers (n = 6). Repeat scans within the same institution, using the same scanner or 2 scanners of the same model, had an average difference in SUVmax of 8% (95% confidence interval, 6%-10%). For test-retest on different scanners at different sites, the average difference in lesion SUVmax was 18% (95% confidence interval, 13%-24%). Normal liver uptake (SUVmean) showed an average difference of 5% (95% confidence interval, 3%-10%) for the same scanner model or institution and 6% (95% confidence interval, 3%-11%) for different scanners from different institutions. Protocol adherence was good; the median difference in injection-to-acquisition time was 2 min (range, 0-11 min). Test-retest SUVmax variability was not explained by available information on protocol deviations or patient or lesion characteristics. Conclusion:18F-FDG PET/CT scanner qualification and calibration can yield highly reproducible test-retest tumor SUV measurements. Our data support use of different qualified scanners of the same model for serial studies. Test-retest differences from different scanner models were greater; more resolution-dependent harmonization of scanner protocols and reconstruction algorithms may be capable of reducing these differences to values closer to same-scanner results.

Prospective Study of Serial 18F-FDG PET and 18F-Fluoride PET to Predict Time to Skeletal-Related Events, Time to Progression, and Survival in Patients with Bone-Dominant Metastatic Breast Cancer.

Assessing therapy response of breast cancer bone metastases is challenging. In retrospective studies, serial 18F-FDG PET was predictive of time to skeletal-related events (tSRE) and time to progression (TTP). 18F-NaF PET improves bone metastasis detection compared with bone scanning. We prospectively tested 18F-FDG PET and 18F-NaF PET to predict tSRE, TTP, and overall survival (OS) in patients with bone-dominant metastatic breast cancer (MBC). Methods: Patients with bone-dominant MBC were imaged with 18F-FDG PET and 18F-NaF PET before starting new therapy (scan1) and again at a range of times centered around approximately 4 mo later (scan2). Maximum standardized uptake value (SUVmax) and lean body mass adjusted standardized uptake (SULpeak) were recorded for a single index lesion and up to 5 most dominant lesions for each scan. tSRE, TTP, and OS were assessed exclusive of the PET images. Univariate Cox regression was performed to test the association between clinical endpoints and 18F-FDG PET and 18F-NaF PET measures. mPERCIST (Modified PET Response Criteria in Solid Tumors) were also applied. Survival curves for mPERCIST compared response categories of complete response+partial response+stable disease versus progressive disease for tSRE, TTP, and OS. Results: Twenty-eight patients were evaluated. Higher 18F-FDG SULpeak at scan2 predicted shorter time to tSRE (P = <0.001) and TTP (P = 0.044). Higher 18F-FDG SUVmax at scan2 predicted a shorter time to tSRE (P = <0.001). A multivariable model using 18F-FDG SUVmax of the index lesion at scan1 plus the difference in SUVmax of up to 5 lesions between scans was predictive for tSRE and TTP. Among 24 patients evaluable by 18F-FDG PET mPERCIST, tSRE and TTP were longer in responders (complete response, partial response, or stable disease) than in nonresponders (progressive disease) (P = 0.007, 0.028, respectively), with a trend toward improved survival (P = 0.1). An increase in the uptake between scans of up to 5 lesions by 18F-NaF PET was associated with longer OS (P = 0.027). Conclusion: Changes in 18F-FDG PET parameters during therapy are predictive of tSRE and TTP, but not OS. mPERCIST evaluation in bone lesions may be useful in assessing response to therapy and is worthy of evaluation in multicenter, prospective trials. Serial 18F-NaF PET was associated with OS but was not useful for predicting TTP or tSRE in bone-dominant MBC.

Estrogen Receptor Binding (18F-FES PET) and Glycolytic Activity (18F-FDG PET) Predict Progression-Free Survival on Endocrine Therapy in Patients with ER+ Breast Cancer.

PURPOSE: 18F-fluoroestradiol (FES) PET scans measure regional estrogen binding, and 18F-fluorodeoxyglucose (FDG) PET measures tumor glycolytic activity. We examined quantitative and qualitative imaging biomarkers of progression-free survival (PFS) in breast cancer patients receiving endocrine therapy. EXPERIMENTAL DESIGN: Ninety patients with breast cancer from an estrogen receptor-positive (ER+), HER2- primary tumor underwent FES PET and FDG PET scans prior to endocrine therapy (63% aromatase inhibitor, 22% aromatase inhibitor and fulvestrant, 15% other). Eighty-four had evaluable data for PFS prediction. RESULTS: Recursive partitioning with 5-fold internal cross-validation used both FES PET and FDG PET measures to classify patients into three distinct response groups. FDG PET identified 24 patients (29%) with low FDG uptake, suggesting indolent tumors. These patients had a median PFS of 26.1 months (95% confidence interval, 11.2-49.7). Of patients with more FDG-avid tumors, 50 (59%) had high average FES uptake, and 10 (12%) had low average FES uptake. These groups had median PFS of 7.9 (5.6-11.8) and 3.3 months (1.4-not evaluable), respectively. Patient and tumor features did not replace or improve the PET measures' prediction of PFS. Prespecified endocrine resistance classifiers identified in smaller cohorts did not individually predict PFS. CONCLUSIONS: A wide range of therapy regimens are available for treatment of ER+ metastatic breast cancer, but no guidelines are established for sequencing these therapies. FDG PET and FES PET may help guide the timing of endocrine therapy and selection of targeted and/or cytotoxic chemotherapy. A multicenter trial is ongoing for external validation. Clin Cancer Res; 23(2); 407-15. ©2016 AACR.

The Reliability of a Standardized Reporting System for the Diagnosis of Appendicitis.

PURPOSE: Computed tomography (CT) is a fast and ubiquitous tool to evaluate intra-abdominal organs and diagnose appendicitis. However, traditional CT reporting does not necessarily capture the degree of uncertainty and indeterminate findings are still common. The purpose of this study was to evaluate the reproducibility of a standardized CT reporting system for appendicitis across a large population and the system's impact on radiologists' certainty in diagnosing appendicitis. METHODS: Using a previously described standardized reporting system, eight radiologists retrospectively evaluated CT scans, blinded to all clinical information, in a stratified random sample of 237 patients from a larger cohort of patients imaged for possible appendicitis (2010-2014). Receiver operating characteristic (ROC) curves and the area under the ROC curve (AUC) were used to evaluate the diagnostic performance of readers for identifying appendicitis. Two-thirds of these scans were randomly selected to be independently read by a second reader, using the original CT reports to balance the number of positive, negative and indeterminate exams across all readers. Inter-reader agreement was evaluated. RESULTS: There were 113 patients with appendicitis (mean age 38, 67% male). Using the standardized report, radiologists were highly accurate at identifying appendicitis (AUC=0.968, 95%CI confidence interval: 0.95, 0.99. Inter-reader agreement was >80% for most objective findings, and certainty in diagnosing appendicitis was high and reproducible (AUC=0.955 and AUC=0.936 for the first and second readers, respectively). CONCLUSIONS: Using a standardized reporting system resulted in high reproducibility of objective CT findings for appendicitis and achieved high diagnostic accuracy in an at-risk population. Predictive tools based on this reporting system may further improve communication about certainty in diagnosis and guide patient management, especially when CT findings are indeterminate.

Non-invasive assessment of liver fibrosis using acoustic structure quantification: comparison with transient elastography in chronic viral hepatitis.

PURPOSE: The purpose of this study was to evaluate the diagnostic efficacy of acoustic structure quantification (ASQ) parameters [mode, average, and focal distribution (FD) ratio] in the staging of hepatic fibrosis in patients with chronic viral hepatitis and to compare it with transient elastography (TE) by using liver biopsy as reference standard. METHODS: We studied 62 patients with chronic viral hepatitis. Each patient underwent ASQ evaluation and liver biopsy; 54 of these patients received TE. Thirty-six participants without any liver disease were enrolled as normal group, who also underwent ASQ evaluation and TE. All three parameters of ASQ were compared with the histologic fibrosis grade according to the METAVIR scoring (F0-F4). Statistical analysis was performed to investigate the correlations and the diagnostic values of ASQ parameters and compare them to TE. RESULTS: All three ASQ parameters and TE were significantly correlated with liver fibrosis stage. Of the ASQ parameters, the mode parameter showed the best correlation (P < 0.001). On the area under the receiver operating characteristic curve (AUROC), the mode parameter of ASQ analysis showed both significant correlation and good accuracy for diagnosis of F ≥ 1, F ≥ 2, and F ≥ 3. These values were significantly better than those of the average and FD ratio parameters in F ≥ 1 and F ≥ 2 (P < 0.05). There was no statistically significant difference in AUROC between the mode parameter and TE in diagnosis of F ≥ 1, F ≥ 2, or F ≥ 3. CONCLUSIONS: The mode parameter is the most reliable ASQ parameter, comparable to TE, as a non-invasive method for the detection and grading of liver fibrosis in patients with chronic viral hepatitis.

Radionuclide methods for breast cancer staging.

Staging at initial presentation is one of the important prognostic factors for patients with breast cancer. Depending on the extent of disease spread, staging is divided into locoregional and distant or systemic. Locoregional staging includes axillary and internal mammary lymph node evaluation and distant or systemic staging includes evaluation of sites beyond the lymph node. Fluorodeoxyglucose-positron emission tomography (FDG-PET) is not sensitive to detect small metastasis in axillary lymph node. The current standard of axillary lymph node staging in early-stage breast cancer is therefore sentinel lymph node biopsy. Internal mammary lymph nodes are not commonly included in routine staging. In advanced-stage breast cancer, FDG-PET and PET/computed tomography (CT) are the modalities of choice to evaluate locoregional and distant metastasis. FDG-PET and PET/CT often detect occult metastasis, which is not visible on any other modalities including diagnostic CT scan. Detection of occult metastasis may potentially change in treatment options. This is particularly important in locally advanced breast cancer, which tends to develop early distant metastasis.

Magnetic resonance imaging of pelvic floor dysfunction.

Pelvic floor dysfunction is largely a complex problem of multiparous and postmenopausal women and is associated with pelvic floor or organ descent. Physical examination can underestimate the extent of the dysfunction and misdiagnose the disorders. Functional magnetic resonance (MR) imaging is emerging as a promising tool to evaluate the dynamics of the pelvic floor and use for surgical triage and operative planning. This article reviews the anatomy and pathology of pelvic floor dysfunction, typical imaging findings, and the current role of functional MR imaging.

Gestatational trophoblastic disease: multimodality imaging assessment with special emphasis on spectrum of abnormalities and value of imaging in staging and management of disease.

Gestational trophoblastic disease is a spectrum of disorders of varying malignant potential arising from trophoblastic cells and encompassing hydatidiform moles and persistent trophoblastic neoplasia. Ultrasound is the initial imaging investigation of choice when gestational trophoblastic disease is suspected. Complete hydatiform mole, the most common form of molar pregnancy, usually has a characteristic "cluster of grapes" appearance, especially on second-trimester ultrasounds. Persistent trophobastic neoplasia usually appears as a focal, hypervascular myometrial mass on pelvic ultrasound. Pelvic magnetic resonance imaging is often used as a problem-solving tool in equivocal or complicated cases of gestational trophoblastic disease to assess the degree of invasion into the myometrium and surrounding tissues. Chest x-ray, brain magnetic resonance imaging, and body computed tomography scans are primarily used for the evaluation of metastatic disease, which usually occurs in the context of choriocarcinomas. Choriocarcinoma metastases are usually hypervascular and have a tendency to bleed, features that are reflected in their imaging appearance.

Between-patient and within-patient (site-to-site) variability in estrogen receptor binding, measured in vivo by 18F-fluoroestradiol PET.

UNLABELLED: Heterogeneity of estrogen receptor (ER) expression may be an important predictor of breast cancer therapeutic response. (18)F-fluoroestradiol PET produces in vivo quantitative measurements of regional estrogen binding in breast cancer tumors. We describe within-patient (site-to-site) and between-patient heterogeneity of lesions in patients scheduled to receive endocrine therapy. METHODS: In 91 patients with a prior ER-positive biopsy, 505 lesions were analyzed for both (18)F-fluoroestradiol and (18)F-FDG uptake and the (18)F-fluoroestradiol/(18)F-FDG uptake ratio. Standardized uptake values (SUVs) were recorded for up to 16 lesions per patient, of 1.5 cm or more and visible on (18)F-FDG PET or conventional staging. Linear mixed-effects regression models examined associations between PET parameters and patient or lesion characteristics and estimated variance components. A reader study of SUV measurements for 9 scans further examined sources of within-patient variability. RESULTS: Average (18)F-fluoroestradiol uptake and (18)F-fluoroestradiol/(18)F-FDG ratio varied greatly across these patients, despite a history of ER-positive disease: about 37% had low or absent (18)F-fluoroestradiol uptake even with marked (18)F-FDG uptake. (18)F-fluoroestradiol SUV and (18)F-fluoroestradiol/(18)F-FDG ratio measurements within patients with multiple lesions were clustered around the patient's average value in most cases. Summarizing these findings, the intraclass correlation coefficient (proportion of total variation that is between-patient) was 0.60 (95% confidence interval, 0.50-0.69) for (18)F-fluoroestradiol SUV and 0.65 (95% confidence interval, 0.56-0.73) for the (18)F-fluoroestradiol/(18)F-FDG ratio. Some within-patient variation in PET measures (22%-44%) was attributable to interobserver variability as measured by the reader study. A subset of patients had mixed uptake, with widely disparate (18)F-fluoroestradiol SUV or (18)F-fluoroestradiol/(18)F-FDG ratio for lesions in the same scan. CONCLUSION: (18)F-fluoroestradiol uptake and the (18)F-fluoroestradiol/(18)F-FDG ratio varied greatly between patients but were usually consistent across lesions in the same scan. The average (18)F-fluoroestradiol SUV and (18)F-fluoroestradiol/(18)F-FDG ratio for a limited sample of lesions appear to provide a reasonable summary of synchronous ER expression for most patients. However, imaging the entire disease burden remains important to identify the subset of patients with mixed uptake, who may be at a critical point in their disease evolution.

Breast Cancer Imaging with Novel PET Tracers.

Whereas (18)F-fluorodeoxyglucose (FDG)-PET/computed tomography has proven to be valuable for breast cancer diagnosis and response evaluation, it is likely that PET radiopharmaceuticals beyond FDG will contribute further to the understanding of breast cancer and thereby further direct breast cancer care. Increasingly specific and quantitative approaches will help direct treatment selection from an ever-expanding and increasing array of targeted breast cancer therapies. This article highlights 4 areas of ongoing research where preliminary patient results look promising: (1) tumor perfusion and angiogenesis, (2) drug delivery and transport, (3) tumor receptor imaging, and (4) early response evaluation. For each area, the biologic background is reviewed and early results are highlighted.