Detection of Primary Breast Carcinoma with a Dedicated, Large-Field-of-View FDG PET Mammography Device: Initial Experience

Advances in Breast PET Instrumentation

Dedicated breast PET scanners currently have a spatial resolution in the 1.5 to 2 mm range, and the ability to provide tomographic images and quantitative data. They are also commercially available from a few vendors. A review of past and recent advances in the development and performance of dedicated breast PET scanners is summarized.

Clustering subtypes of breast cancer by combining immunohistochemistry profiles and metabolism characteristics measured using FDG PET/CT

BACKGROUND

The aim of this study was to investigate the effect of combining immunohistochemical profiles and metabolic information to characterize breast cancer subtypes.

METHODS

This retrospective study included 289 breast tumors from 284 patients who underwent preoperative 18 F-fluorodeoxyglucose (FDG) positron emission tomography/ computed tomography (PET/CT). Molecular subtypes of breast cancer were classified as Hormonal, HER2, Dual (a combination of both Hormonal and HER2 features), and triple-negative (TN). Histopathologic findings and immunohistochemical results for Ki-67, EGFR, CK 5/6, and p53 were also analyzed. The maximum standardized uptake value (SUV) measured from FDG PET/CT was used to evaluate tumoral glucose metabolism.

RESULTS

Overall, 182, 24, 47, and 36 tumors were classified as Hormonal, HER2, Dual, and TN subtypes, respectively. Molecular profiles of tumor aggressiveness and the tumor SUV revealed a gradual increase from the Hormonal to the TN type. The tumor SUV was significantly correlated with tumor size, expression levels of p53, Ki-67, and EGFR, and nuclear grade (all p < 0.001). In contrast, the tumor SUV was negatively correlated with the expression of estrogen receptors (r = - 0.234, p < 0.001) and progesterone receptors (r = - 0.220, p < 0.001). Multiple linear regression analysis revealed that histopathologic markers explained tumor glucose metabolism (adjusted R-squared value 0.238, p < 0.001). Tumor metabolism can thus help define breast cancer subtypes with aggressive/adverse prognostic features.

CONCLUSIONS

Metabolic activity measured using FDG PET/CT was significantly correlated with the molecular alteration profiles of breast cancer assessed using immunohistochemical analysis. Combining molecular markers and metabolic information may aid in the recognition and understanding of tumor aggressiveness in breast cancer and be helpful as a prognostic marker.

Performance comparison of a dedicated total breast PET system with a clinical whole-body PET system: a simulation study

This paper presents a novel PET geometry for breast cancer imaging. The scanner consists of a 'stadium' (a rectangle with two semi-circles on opposite sides) shaped ring, along with anterior and posterior panels to provide high sensitivity and high spatial resolution for an imaging field-of-view (FOV) that include both breasts, mediastinum and axilla. We simulated this total-breast PET system using GATE and reconstructed the coincidence events using a GPU-based list-mode image reconstruction implementing maximum likelihood expectation-maximization (ML-EM) algorithm. The rear-panel is made up of a single layer of LSO crystals (3.2 × 3.2 × 20 mm³each), while the 'stadium'-shaped elongated ring and the anterior panel are made with dual-layered LSO crystals (1.6 × 1.6 × 6 mm³each). The energy resolution and coincidence resolving time of all detectors are assumed to be 12% and 250 ps full-width-at-half-maximum, respectively. Various sized simulated lesions (4, 5, 6 mm) having 4:1, 5:1, and 6:1 lesion-to-background radioactivity concentration ratios, mimicking different biological uptakes, were strategically located throughout a volumetric torso phantom. We compared system sensitivity and lesion detectability of the dedicated total-breast PET system to a state-of-the-art clinical whole-body PET scanner. The mean sensitivity of the total-breast PET system is 3.21 times greater than that of a whole-body PET scanner in the breast regions. The total-breast PET system also provides better contrast-recovery coefficients for lesions of all sizes and lesion-to-background ratios in the breast when compared to a reference clinical whole-body PET scanner. Receiver operating characteristics (ROC) study shows the area under the ROC curve is 0.948 and 0.924 for the total-breast system and the whole-body PET scanner, respectively, in the detection of 4 mm diameter lesions with 4:1 lesion-to-background ratio. This study demonstrates our novel geometry can provide an imaging FOV larger than conventional PEM systems to simultaneously image both breasts, chest wall and axillae with significantly improved lesion detectability in the breasts when compared to a whole-body PET scanner.

Role of 18F-fluorodeoxyglucose positron emission tomography/computed tomography in the evaluation of breast carcinoma: Indications and pitfalls with illustrative case examples

Whole-body ¹⁸F-fluorodeoxyglucose positron emission tomography (PET) has been used extensively in the last decade for the primary staging and restaging and to assess response to therapy in these patients. We aim to discuss the diagnostic performance of PET/computed tomography in the initial staging of breast carcinoma including the locally advanced disease and to illustrate its role in restaging the disease and in the assessment of response to therapy, particularly after the neoadjuvant chemotherapy. Causes of common pitfalls during image interpretations will be also discussed.

Positron Emission Mammography (PEM) in the diagnosis of breast cancer: A systematic review and economic evaluation

Background: Positron Emission Mammography (PEM) is an imaging technique which is increasing focuses on imaging the chest instead of imaging the whole body. The aim of this study was to conduct a systematic review of the clinical efficacy and coste-ffectiveness of PEM technology, as compared with PET, as a diagnostic method used for breast cancer patients.

Methods: The present study was a Health Technology Assessment (HTA), which was conducted via a systematic review of clinical efficacy and cost-effectiveness of the methods based on domestic evidence. To evaluate the efficacy of the PEM diagnostic method, as compared with PET, we used efficacy indices, including Sensitivity, Specificity, Accuracy, PPV, and NPV. The required data were collected through a meta-analysis of studies published in electronic databases from 1990 to 2016. In addition, direct costs in both methods were estimated and finally, a cost-effectiveness analysis was performed using the results of the study. Also, a one-way sensitivity analysis was performed to examine the effects of parameters’ uncertainty in the model. In this study, we used STATA software to integrate the results of studies with similar parameters.

Results: A total of 722 cases (N) were obtained from the five final studies. The results of the meta-analysis performed on the collected data showed that the two methods were identical in terms of the Specificity and PPV parameters. However, as to Sensitivity, NPV, and Accuracy parameters, the PEM method was superior to the PET for diagnosis of primary breast cancer. The total cost of using PEM and PET was $1737385.7 and $1940903.5, respectively, and the cost of a one-time scan (cost per unit) using PEM and PET devices was $86.82 and $157.63, respectively. As compared with the PET method, the use of the PEM diagnostic method for diagnosis of breast cancer was cost-effective in terms of all the five studied parameters (it was definitely cost-effective for four parameters and was also considered as cost-effective for another index, since ICER was below the threshold).

Conclusion: The results showed that the use of PEM technology for the diagnosis of primary breast cancer is more cost-effective than PET technology; thus, due to the wide range of PET technology in different fields, it is recommended that this method should be used in other areas of priority.

Progress and Future Trends in PET/CT and PET/MRI Molecular Imaging Approaches for Breast Cancer

Breast cancer is a major disease with high morbidity and mortality in women worldwide. Increased use of imaging biomarkers has been shown to add more information with clinical utility in the detection and evaluation of breast cancer. To date, numerous studies related to PET-based imaging in breast cancer have been published. Here, we review available studies on the clinical utility of different PET-based molecular imaging methods in breast cancer diagnosis, staging, distant-metastasis detection, therapeutic and prognostic prediction, and evaluation of therapeutic responses. For primary breast cancer, PET/MRI performed similarly to MRI but better than PET/CT. PET/CT and PET/MRI both have higher sensitivity than MRI in the detection of axillary and extra-axillary nodal metastases. For distant metastases, PET/CT has better performance in the detection of lung metastasis, while PET/MRI performs better in the liver and bone. Additionally, PET/CT is superior in terms of monitoring local recurrence. The progress in novel radiotracers and PET radiomics presents opportunities to reclassify tumors by combining their fine anatomical features with molecular characteristics and develop a beneficial pathway from bench to bedside to predict the treatment response and prognosis of breast cancer. However, further investigation is still needed before application of these modalities in clinical practice. In conclusion, PET-based imaging is not suitable for early-stage breast cancer, but it adds value in identifying regional nodal disease and distant metastases as an adjuvant to standard diagnostic imaging. Recent advances in imaging techniques would further widen the comprehensive and convergent applications of PET approaches in the clinical management of breast cancer.

Radiation Doses and Risks in Breast Screening

This article describes radiation doses and cancer risks of digital breast imaging technologies used for breast cancer detection. These include digital mammography (DM), digital breast tomosynthesis (DBT), and newer technologies such as contrast-enhanced digital or spectral mammography (CEM), whole-breast computed tomography, breast-specific gamma imaging (BSGI), molecular breast imaging (MBI), and positron emission mammography (PEM). This article describes the basis for radiation risk estimates, compares radiation doses and risks, and provides benefit-to-radiation-risk ratios for different breast imaging modalities that use ionizing radiation. Current x-ray-based screening modalities such as DM and DBT have small to negligible risks of causing radiation-induced cancers in women of normal screening age. Possible new screening modalities such as CEM have similar small cancer risks. Potential screening modalities that involve radionuclide injection such as BSGI, MBI, and PEM have significantly higher cancer risks unless efficient detection systems and reduced administered doses are used. Benefit-to-radiation-risk estimates are highly favorable for screening with DM and other modalities having comparable (or higher) cancer detection rates and comparably low radiation doses.

Newly-Developed Positron Emission Mammography (PEM) Device for the Detection of Small Breast Cancer

Positron emission mammography (PEM) has higher detection sensitivity for breast cancer compared with whole-body positron emission tomography (PET) due to higher spatial resolution. We have developed a new PEM device with high resolution over a wide field of view. This PEM device comprises novel scintillation crystals, praseodymium-doped lutetium aluminum garnet (Pr:LuAG). In the present study, the clinical use of the newly developed PEM for the detection of small breast cancer was compared with that of the conventional PET-computed tomography (PET/CT). Eighty-two patients with breast cancer less than 20 mm (UICC T1) participated in this study, including 23 patients with T1a or T1b breast cancer (less than 10 mm). Histologically-proved lesions were examined by PET/CT and PEM on the same day after injection of [¹⁸F]fluoro-2-deoxy-2-fluoro-D-glucose ([¹⁸F]FDG), a marker of glycolytic activity. The newly developed PEM showed better sensitivity of cancer detection compared with PET/CT especially in case of the small T1a or T1b lesions. Moreover, when the conventional PET/CT and new PEM were combined, the detection sensitivity with [¹⁸F]FDG molecular imaging for T1 (N = 82) and T1a plus T1b breast cancer (N = 23) were 90% and 70%, respectively. The uptake of [¹⁸F]FDG was proportional to the histological malignancy of breast cancer. Using the newly-developed PEM with [¹⁸F]FDG, we are able to identify and characterize exactly the small breast tumors less than 10 mm in combination with the conventional PET/CT. These data indicate that PEM and PET/CT are synergic and complementary for the detection of small breast cancer.

A dedicated breast-PET/CT scanner: Evaluation of basic performance characteristics

PURPOSE

Application of advanced imaging techniques, such as PET and x ray CT, can potentially improve detection of breast cancer. Unfortunately, both modalities have challenges in the detection of some lesions. The combination of the two techniques, however, could potentially lead to an overall improvement in diagnostic breast imaging. The purpose of this investigation is to test the basic performance of a new dedicated breast-PET/CT.

METHODS

The PET component consists of a rotating pair of detectors. Its performance was evaluated using the NEMA NU4-2008 protocols. The CT component utilizes a pulsed x ray source and flat panel detector mounted on the same gantry as the PET scanner. Its performance was assessed using specialized phantoms. The radiation dose to a breast during CT imaging was explored by the measurement of free-in-air kerma and air kerma measured at the center of a 16 cm-diameter PMMA cylinder. Finally, the combined capabilities of the system were demonstrated by imaging of a micro-hot-rod phantom.

RESULTS

Overall, performance of the PET component is comparable to many pre-clinical and other dedicated breast-PET scanners. Its spatial resolution is 2.2 mm, 5 mm from the center of the scanner using images created with the single-sliced-filtered-backprojection algorithm. Peak NECR is 24.6 kcps; peak sensitivity is 1.36%; the scatter fraction is 27%. Spatial resolution of the CT scanner is 1.1 lp/mm at 10% MTF. The free-in-air kerma is 2.33 mGy, while the PMMA-air kerma is 1.24 mGy. Finally, combined imaging of a micro-hot-rod phantom illustrated the potential utility of the dual-modality images produced by the system.

CONCLUSION

The basic performance characteristics of a new dedicated breast-PET/CT scanner are good, demonstrating that its performance is similar to current dedicated PET and CT scanners. The potential value of this system is the capability to produce combined duality-modality images that could improve detection of breast disease. The next stage in development of this system is testing with more advanced phantoms and human subjects.

Recent Advances in Breast-Specific Imaging

Background

Imaging the breast is a vital component not only for breast cancer screening, but also for diagnosis, evaluation, treatment, and follow-up of patients with breast cancer.

Methods

The author reviews recent advances and also provides her personal experience in describing the status of digital mammography, computer-aided detection, dedicated magnetic resonance imaging (MRI), and positron-emission mammography for evaluating the breast.

Results

Full-field digital mammography is superior to standard mammography in women under 50 years of age and in those with dense breasts. Computer-aided detection assists inexperienced mammographers and enhances detection of microcalcifications in dense breasts. Breast MRI is useful in preoperative evaluation, clarification of indeterminate mammograms, and follow-up of BRCA mutation carriers. The specificity of MRI remains problematic, however. Positron-emission mammography promises enhanced detection of ductal carcinoma in situ (DCIS), even when not associated with microcalcifications, and should aid surgical planning.

Conclusions

These four significant advances in breast imaging have all improved the sensitivity of detecting breast abnormalities. Cost issues, however, may limit the widespread application of these advances.

Comparison of Diagnostic Performance of Three-Dimensional Positron Emission Mammography versus Whole Body Positron Emission Tomography in Breast Cancer

Objective

To compare the diagnostic performance of three-dimensional (3D) positron emission mammography (PEM) versus whole body positron emission tomography (WBPET) for breast cancer.

Methods

A total of 410 women with normal breast or benign or highly suspicious malignant tumors were randomized at 1 : 1 ratio to undergo 3D-PEM followed by WBPET or WBPET followed by 3D-PEM. Lumpectomy or mastectomy was performed on eligible participants after the scanning.

Results

The sensitivity and specificity of 3D-PEM were 92.8% and 54.5%, respectively. WBPET showed a sensitivity of 95.7% and specificity of 56.8%. After exclusion of the patients with lesions beyond the detecting range of the 3D-PEM instrument, 3D-PEM showed higher sensitivity than WBPET (97.0% versus 95.5%, P = 0.913), particularly for small lesions (<1 cm) (72.0% versus 60.0%, P = 0.685).

Conclusions

The 3D-PEM appears more sensitive to small lesions than WBPET but may fail to detect lesions that are beyond the detecting range. This study was approved by the Ethics Committee (E2012052) at the Tianjin Medical University Cancer Institute and Hospital (Tianjin, China). The instrument positron emission mammography (PEMi) was approved by China State Food and Drug Administration under the registration number 20153331166.

Multimodal breast cancer imaging using coregistered dynamic diffuse optical tomography and digital breast tomosynthesis

Diffuse optical tomography (DOT) is emerging as a noninvasive functional imaging method for breast cancer diagnosis and neoadjuvant chemotherapy monitoring. In particular, the multimodal approach of combining DOT with x-ray digital breast tomosynthesis (DBT) is especially synergistic as DBT prior information can be used to enhance the DOT reconstruction. DOT, in turn, provides a functional information overlay onto the mammographic images, increasing sensitivity and specificity to cancer pathology. We describe a dynamic DOT apparatus designed for tight integration with commercial DBT scanners and providing a fast (up to 1 Hz) image acquisition rate to enable tracking hemodynamic changes induced by the mammographic breast compression. The system integrates 96 continuous-wave and 24 frequency-domain source locations as well as 32 continuous wave and 20 frequency-domain detection locations into low-profile plastic plates that can easily mate to the DBT compression paddle and x-ray detector cover, respectively. We demonstrate system performance using static and dynamic tissue-like phantoms as well as in vivo images acquired from the pool of patients recalled for breast biopsies at the Massachusetts General Hospital Breast Imaging Division.

Higher breast cancer conspicuity on dbPET compared to WB-PET/CT

OBJECTIVES

The purpose of this study was to evaluate lesion detectability of a dedicated breast positron-emission tomography (dbPET) scanner for breast cancers with an updated reconstruction mode, comparing it to whole-body positron-emission tomography/computed tomography (WB-PET/CT).

MATERIALS AND METHODS

A total of 179 histologically-proven breast cancer lesions in 150 females who underwent both WB-PET/CT and dbPET with ¹⁸F-fluorodeoxyglucose were retrospectively analyzed. The patient/breast/lesion-based sensitivities based on visual analysis were compared between dbPET and WB-PET/CT. For lesions visible on both PET images, SUVmax values of the tumors were measured, and tumor-to-background ratios (T/B ratios) of SUVmax were compared between the two scans. Subgroup analyses according to clinical tumor stage, histopathology and histological grade were also performed.

RESULTS

Patient/breast/lesion-based sensitivities were 95%, 95%, and 92%, respectively, for dbPET, and 95%, 94%, and 88%, respectively, for WB-PET/CT. Mean±standard deviation SUVmax values of FDG-avid tumors were 13.0±9.7 on dbPET and 6.4±4.8 on WB-PET. T/B ratios were also significantly higher in dbPET than in WB-PET/CT (8.1±7.1 vs. 5.1±4.5). In the subgroup analysis, no significant differences in sensitivities between dbPET and WB-PET/CT were found. However, T/B ratios of dbPET were significantly higher than those of WB-PET/CT in cT1c, cT2, cT3, invasive cancer, invasive carcinoma of no special type, mucinous carcinoma and Grades 1-3.

CONCLUSION

No significant differences in sensitivities were identified between dbPET using an updated reconstruction mode and WB-PET/CT; however, T/B ratios of dbPET were significantly higher than those of WB-PET/CT, indicating higher tumor conspicuity on dbPET.

Performance evaluation of a high resolution dedicated breast PET scanner

PURPOSE

Early stage breast cancers may not be visible on a whole-body PET scan. To overcome whole-body PET limitations, several dedicated breast positron emission tomography (DbPET) systems have emerged nowadays aiming to improve spatial resolution. In this work the authors evaluate the performance of a high resolution dedicated breast PET scanner (Mammi-PET, Oncovision).

METHODS

Global status, uniformity, sensitivity, energy, and spatial resolution were measured. Spheres of different sizes (2.5, 4, 5, and 6 mm diameter) and various 18 fluorodeoxyglucose ((18)F-FDG) activity concentrations were randomly inserted in a gelatine breast phantom developed at our institution. Several lesion-to-background ratios (LBR) were simulated, 5:1, 10:1, 20:1, 30:1, and 50:1. Images were reconstructed using different voxel sizes. The ability of experienced reporters to detect spheres was tested as a function of acquisition time, LBR, sphere size, and matrix reconstruction voxel size. For comparison, phantoms were scanned in the DbPET camera and in a whole body PET (WB-PET). Two patients who just underwent WB-PET/CT exams were imaged with the DbPET system and the images were compared.

RESULTS

The measured absolute peak sensitivity was 2.0%. The energy resolution was 24.0% ± 1%. The integral and differential uniformity were 10% and 6% in the total field of view (FOV) and 9% and 5% in the central FOV, respectively. The measured spatial resolution was 2.0, 1.9, and 1.7 mm in the radial, tangential, and axial directions. The system exhibited very good detectability for spheres ≥4 mm and LBR ≥10 with a sphere detection of 100% when acquisition time was set >3 min/bed. For LBR = 5 and acquisition time of 7 min the detectability was 100% for spheres of 6 mm and 75% for spheres of 5, 4, and 2.5 mm. Lesion WB-PET detectability was only comparable to the DbPET camera for lesion sizes ≥5 mm when acquisition time was >3 min and LBR > 10.

CONCLUSIONS

The DbPET has a good performance for its clinical use and shows an improved resolution and lesion detectability of small lesions compared to WB-PET.

Comparative analysis of imaging sensitivity of positron emission mammography and whole-body PET in relation to tumor size

OBJECTIVE

Positron emission mammography (PEM) consists of a dedicated PET scanner for breast imaging with a higher spatial resolution than whole-body PET (WBPET) scanners. This study compared the imaging sensitivity of PEM with WBPET in relation to tumor size.

METHODS

Fifty-four Japanese women younger than 50 years with histologically confirmed breast lesions were retrospectively enrolled. Positron emission mammography and WBPET were conducted on the same day. Positron emission mammography and WBPET images were blindly evaluated and compared with histopathology. Tumors were classified into 3 groups based on size as follows: group 1, 1 cm or smaller; group 2, 1 to 2 cm; and group 3, larger than 2 cm. The sensitivities of PEM and WBPET were compared in overall subjects and in each size group.

RESULTS

In visual analysis, the overall imaging sensitivity was 78.6% (33/42) for PEM and 47.6% (20/42) for WBPET. The overall sensitivity of PEM was significantly higher than that of WBPET (P < 0.001). The differences in sensitivities between PEM and WBPET were larger in smaller tumors: group 1 (66.7% vs 13.3%), group 2 (63.4% vs 36.4%), and group 3 (100.0% vs 87.5%). The sensitivity of PEM was significantly higher than that of WBPET in group 1 (P = 0.008); however, no significant differences were seen in group 2 (P = 0.500) or group 3 (P = 0.250). Overall, the imaging specificity of PEM and WEBPET was 90.6% (60/66) and 93.9% (62/66), respectively.

CONCLUSIONS

The imaging sensitivity of PEM was higher than that of WBPET in Japanese women younger than 50 years. Positron emission mammography showed significant sensitivity in tumors smaller than 1 cm, which has been a weak point for WBPET.

Arrays of Segmented, Tapered Light Guides for Use with Large, Planar Scintillation Detectors

Metabolic imaging techniques can potentially improve detection and diagnosis of cancer in women with radiodense and/or fibrocystic breasts. Our group has previously developed a high-resolution positron emission tomography imaging and biopsy device (PEM-PET) to detect and guide the biopsy of suspicious breast lesions. Initial testing revealed that the imaging field-of-view (FOV) of the scanner was smaller than the physical size of the detector's active area, which could hinder sampling of breast areas close to the chest wall. The purpose of this work was to utilize segmented, tapered light guides for optically coupling the scintillator arrays to arrays of position-sensitive photomultipliers to increase both the active FOV and identification of individual scintillator elements. Testing of the new system revealed that the optics of these structures made it possible to discern detector elements from the complete active area of the detector face. In the previous system the top and bottom rows and left and right columns were not identifiable. Additionally, use of the new light guides increased the contrast of individual detector elements by up to 129%. Improved element identification led to a spatial resolution increase by approximately 12%. Due to attenuation of light in the light guides the detector energy resolution decreased from 18.5% to 19.1%. Overall, these improvements should increase the field-of-view and spatial resolution of the dedicated breast-PET system.

Performance Evaluation of a New Dedicated Breast PET Scanner Using NEMA NU4-2008 Standards

The aim of this work was to evaluate the performance characteristics of a newly developed dedicated breast PET scanner, according to National Electrical Manufacturers Association (NEMA) NU 4-2008 standards.

METHODS

The dedicated breast PET scanner consists of 4 layers of a 32 × 32 lutetium oxyorthosilicate-based crystal array, a light guide, and a 64-channel position-sensitive photomultiplier tube. The size of a crystal element is 1.44 × 1.44 × 4.5 mm. The detector ring has a large solid angle with a 185-mm aperture and an axial coverage of 155.5 mm. The energy windows at depth of interaction for the first and second layers are 400-800 keV, and those at the third and fourth layers are 100-800 keV. A fixed timing window of 4.5 ns was used for all acquisitions. Spatial resolution, sensitivity, counting rate capabilities, and image quality were evaluated in accordance with NEMA NU 4-2008 standards. Human imaging was performed in addition to the evaluation.

RESULTS

Radial, tangential, and axial spatial resolution measured as minimal full width at half maximum approached 1.6, 1.7, and 2.0 mm, respectively, for filtered backprojection reconstruction and 0.8, 0.8, and 0.8 mm, respectively, for dynamic row-action maximum-likelihood algorithm reconstruction. The peak absolute sensitivity of the system was 11.2%. Scatter fraction at the same acquisition settings was 30.1% for the rat-sized phantom. Peak noise-equivalent counting rate and peak true rate for the ratlike phantom was 374 kcps at 25 MBq and 603 kcps at 31 MBq, respectively. In the image-quality phantom study, recovery coefficients and uniformity were 0.04-0.82 and 1.9%, respectively, for standard reconstruction mode and 0.09-0.97 and 4.5%, respectively, for enhanced-resolution mode. Human imaging provided high-contrast images with restricted background noise for standard reconstruction mode and high-resolution images for enhanced-resolution mode.

CONCLUSION

The dedicated breast PET scanner has excellent spatial resolution and high sensitivity. The performance of the dedicated breast PET scanner is considered to be reasonable enough to support its use in breast cancer imaging.

Where does radioimmunotherapy fit in the management of breast cancer?

Breast cancer is one of the most commonly diagnosed malignancies and is the main cause of death in women aged 40-49 years. Metastatic breast cancer is a heterogeneous disease that has a variety of different clinical presentations, ranging from solitary metastatic lesion to diffuse and multiple organ involvement. The biological heterogeneity of metastatic breast cancer has led to its unpredictable clinical behavior. One of the major challenges, therefore, is to identify predictive and prognostic models facilitating the selection of patients who can benefit from more aggressive and potentially curative options. This article provides an overview of the current management of metastatic breast cancer with focused emphasis on radioimmunotherapy.

Nuclear imaging of the breast: translating achievements in instrumentation into clinical use

Approaches to imaging the breast with nuclear medicine and∕or molecular imaging methods have been under investigation since the late 1980s when a technique called scintimammography was first introduced. This review charts the progress of nuclear imaging of the breast over the last 20 years, covering the development of newer techniques such as breast specific gamma imaging, molecular breast imaging, and positron emission mammography. Key issues critical to the adoption of these technologies in the clinical environment are discussed, including the current status of clinical studies, the efforts at reducing the radiation dose from procedures associated with these technologies, and the relevant radiopharmaceuticals that are available or under development. The necessary steps required to move these technologies from bench to bedside are also discussed.

Improving PET imaging for breast cancer using virtual pinhole PET half-ring insert

A PET insert with detector having smaller crystals and placed near a region of interest in a conventional PET scanner can improve image resolution locally due to the virtual-pinhole PET (VP-PET) effect. This improvement is from the higher spatial sampling of the imaging area near the detector. We have built a prototype half-ring PET insert for head-and-neck cancer imaging applications. In this paper, we extend the use of the insert to breast imaging and show that such a system provides high resolution images of breast and axillary lymph nodes while maintaining the full imaging field of view capability of a clinical PET scanner. We characterize the resolution and contrast recovery for tumors across the imaging field of view. First, we model the system using Monte Carlo methods to determine its theoretical limit of improvement. Simulations were conducted with hot spherical tumors embedded in background activity at tumor-to-background contrast ranging from 3:1 to 12:1. Tumors are arranged in a Derenzo-like pattern with their diameters ranging from 2 to 12 mm. Experimental studies were performed using a chest phantom with cylindrical breast attachment. Tumors of different sizes arranged in a Derenzo-like pattern with tumor-to-background ratio of 6:1 are inserted into the breast phantom. Imaging capability of mediastinum and axillary lymph nodes is explored. Both Monte Carlo simulations and experiment show clear improvement in image resolution and contrast recovery with VP-PET half-ring insert. The degree of improvement in resolution and contrast recovery depends on location of the tumor. The full field of view imaging capability is shown to be maintained. Minor artifacts are introduced in certain regions.

Diagnostic and prognostic application of positron emission tomography in breast imaging: emerging uses and the role of PET in monitoring treatment response

Positron emission tomography (PET) is an imaging modality that using radiotracers, permits real-time dynamic monitoring of biologic processes such as cell metabolic behavior and proliferation, and has proven useful as a research tool for understanding tumor biology. While it does not have a well-defined role in breast cancer for the purposes of screening, diagnosis, or prognosis, emerging PET technologies and uses could expand the applications of PET in breast cancer. Positron emission mammography may provide an alternative adjunct imaging modality for the screening and diagnosis of high-risk patients unable to tolerate MRI. The development of radiotracers with the ability to measure hormonal activity could provide a non-invasive way to assess hormone receptor status and functionality. Finally, the role of PET technologies in monitoring early treatment response may prove particularly useful to research involving new therapeutic interventions.

The current status of positron emission mammography in breast cancer diagnosis

Mammography is currently the standard breast cancer screening procedure, even though it is constrained by low specificity in the detection of malignancy and low sensitivity in women with dense breast tissue. Modern imaging modalities, such as magnetic resonance imaging (MRI), have been developed in an effort to replace or complement mammography, because the early detection of breast cancer is critical for efficient treatment and long-term survival of patients. Nuclear medicine imaging technology has been introduced in the field of oncology with the development of positron emission tomography (PET), positron emission tomography/computed tomography (PET/CT) and, ultimately, positron emission mammography (PEM). PET offers the advantage of precise diagnosis, by measuring metabolism with the use of a radiotracer and identifying changes at the cellular level. PET/CT imaging allows for a more accurate assessment by merging the anatomic localization to the functional image. However, both techniques have not yet been established as diagnostic tools in early breast cancer detection, primarily because of low sensitivity, especially for sub-centimeter and low-grade tumors. PEM, a breast-specific device with increased spatial resolution, has been developed in order to overcome these limitations. It has demonstrated higher detectability than PET/CT and comparable or better sensitivity than MRI. The ability to target the lesions visible in PEM with PEM-guided breast biopsy systems adds to its usability in the early diagnosis of breast cancer. The results from recent studies summarized in this review indicate that PEM may prove to be a useful first-line diagnostic tool, although further evaluation and improvement are required.

Quantification with a dedicated breast PET/CT scanner

PURPOSE

Dedicated breast PET/CT is expected to have utility in local staging, surgical planning, monitoring of therapy response, and detection of residual disease for breast cancer. Quantitative metrics will be integral to several such applications. The authors present a validation of fully 3D data correction schemes for a custom built dedicated breast PET/CT (DbPET/CT) scanner via (18)F-FDG phantom scans.

METHODS

A component-based normalization was implemented, live-time was estimated with a multicomponent model, and a variance reduced randoms estimate was computed from delayed coincidences. Attenuation factors were calculated by using a CT based segmentation scheme while scatter was computed using a Monte Carlo (MC) simulation method. As no performance standard currently exists for breast PET systems, custom performance tests were created based on prior patient imaging results. Count-rate linearity for live-time and randoms corrections was measured with a decay experiment for a solid polyethylene cylinder phantom with an offset line source. A MC simulation was used to validate attenuation correction, a multicompartment phantom with asymmetric activity distribution provided an assessment of scatter correction, and image uniformity after geometric and detector normalization was measured from a high count scan of a uniform cylinder phantom. Raw data were reconstructed with filtered back projection (FBP) after Fourier rebinning. To quantify performance absolute activity concentrations, contrast recovery coefficients and image uniformity were calculated through region of interest analysis.

RESULTS

The most significant source of error was attributed to mispositioning of events due to pile-up, presenting in count-related axial and transaxial nonuniformities that were not corrected for with the normalization method used here. Within the range of singles counts observed during clinical trials residual error after applying all corrections was comparable to that of a commercial whole body PET/CT system.

CONCLUSIONS

The results suggest that DbPET/CT is capable of producing quantitative images under the operating conditions expected during patient imaging.

Molecular Imaging in Breast Cancer: From Whole-Body PET/CT to Dedicated Breast PET

Positron emission tomography (PET), with or without integrated computed tomography (CT), using 18F-fluorodeoxyglucose (FDG) is based on the principle of elevated glucose metabolism in malignant tumors, and its use in breast cancer patients is frequently being investigated. It has been shown useful for classification, staging, and response monitoring, both in primary and recurrent disease. However, because of the partial volume effect and limited resolution of most whole-body PET scanners, sensitivity for the visualization of small tumors is generally low. To improve the detection and quantification of primary breast tumors with FDG PET, several dedicated breast PET devices have been developed. In this nonsystematic review, we shortly summarize the value of whole-body PET/CT in breast cancer and provide an overview of currently available dedicated breast PETs.

Characterization of a high-resolution hybrid DOI detector for a dedicated breast PET/CT scanner

The aim of this study is to design and test a new high-resolution hybrid depth of interaction (DOI) detector for a dedicated breast PET/CT scanner. Two detectors have been designed and built. The completed detectors are based on a 14 × 14 array of 1.5 × 1.5 × 20 mm(3) unpolished lutetium orthosilicate scintillation crystals, with each element coated in a 50 μm layer of reflective material. The detector is read out from both ends using a position-sensitive photomultiplier tube (PSPMT) and a large active area (20 × 20 mm(2)) avalanche photodiode (APD) to enable acquisition of DOI information. Nuclear instrumentation modules were used to characterize the detectors' performances in terms of timing, intrinsic spatial resolution (ISR) and energy resolution, as well as DOI resolution with a dual-ended readout configuration. Measurements with the APD were performed at a temperature of 10 °C. All crystals were identified at all depths, even though the signal amplitude from the PSPMT decreases with depth away from it. We measured a timing resolution of 2.4 ns, and an average energy resolution of 19%. The mean ISR was measured to be 1.2 mm for crystals in the central row of the array for detectors in the face-to-face position. Two off-center positions were measured corresponding to 26° and 51° oblique photon incidence, and the mean ISR at these positions was 1.5 and 1.7 mm, respectively. The average DOI resolution across all crystals and depths was measured to be 2.9 mm (including the beam width of 0.6 mm). This detector design shows good promise as a high-resolution detector for a dedicated breast PET/CT scanner.

Advances in molecular imaging for breast cancer detection and characterization

Advances in our ability to assay molecular processes, including gene expression, protein expression, and molecular and cellular biochemistry, have fueled advances in our understanding of breast cancer biology and have led to the identification of new treatments for patients with breast cancer. The ability to measure biologic processes without perturbing them in vivo allows the opportunity to better characterize tumor biology and to assess how biologic and cytotoxic therapies alter critical pathways of tumor response and resistance. By accurately characterizing tumor properties and biologic processes, molecular imaging plays an increasing role in breast cancer science, clinical care in diagnosis and staging, assessment of therapeutic targets, and evaluation of responses to therapies. This review describes the current role and potential of molecular imaging modalities for detection and characterization of breast cancer and focuses primarily on radionuclide-based methods.

Is 18F-FDG PET accurate to predict neoadjuvant therapy response in breast cancer? A meta-analysis

Clinical evidence regarding the value of (18)F-FDG PET for therapy responses assessment in breast cancer is increasing. The objective of this study is to evaluate the accuracy of (18)F-FDG PET in predicting responses to neoadjuvant therapies with meta-analysis and explore its optimal regimen for clinical use. Articles in English language relating to the accuracy of (18)F-FDG PET for this utility were retrieved. Methodological quality was assessed by QUADAS tool. Pooled estimation and subgroup analysis data were obtained by statistical analysis. Nineteen studies met the inclusion criteria and involved 920 pathologically confirmed patients in total (mean age 49.8 years, all female). Methodological quality was relatively high. To predict histopathological response in primary breast lesions by PET, the pooled sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic odds ratio were 84% (95% CI, 78-88%), 66% (95% CI, 62-70%), 50% (95% CI, 44-55%), 91% (95% CI, 87-94%), and 11.90 (95% CI, 6.33-22.36), respectively. In regional lymph nodes, sensitivity and NPV of PET were 92% (95% CI, 83-97%) and 88% (95% CI, 76-95%), respectively. Subgroup analysis showed that performing a post-therapy (18)F-FDG PET early (after the 1st or 2nd cycle of chemotherapy) was significantly better than later (accuracy 76% vs. 65%, P = 0.001). Furthermore, the best correlation with pathology was yielded by employing a reduction rate (RR) cutoff value of standardized uptake value between 55 and 65%. (18)F-FDG PET is useful to predict neoadjuvant therapy response in breast cancer. However, the relatively low specificity and PPV still call for caution. It is suggested to perform PET in an earlier course of therapy and use RR cutoff value between 55 and 65%, which might potentially identify non-responders early. However, further prospective studies are warranted to assess this regimen and adequately position PET in treatment management.

Investigating the limit of detectability of a positron emission mammography device: a phantom study

PURPOSE

A new positron emission mammography (PEM) device (PEM Flex Solo II, Naviscan Inc., San Diego, CA) has recently been introduced and its performance characteristics have been documented. However, no systematic assessment of its limit of detectability has been evaluated. The aim of this work is to investigate the limit of detectability of this new PEM system using a novel, customized breast phantom.

METHODS

Two sets of F-18 infused gelatin breast phantoms of varying thicknesses (2, 4, 6, and 8 cm) were constructed with and without (blank) small, shell-less contrast objects (2 mm thick disks) of varying diameters (3-14.5 mm) [volumes: 0.15-3.3 cc] and activity concentration to background ratio (ACR) (2.7-58). For the phantom set with contrast objects, the disks were placed centrally inside the phantoms and both phantom sets were imaged for a period of 10 min on the PEM device. In addition, scans for the 2 and 6 cm phantoms were repeated at different times (0, 90, and 150 min) post phantom construction to evaluate the impact of total activity concentration (count density) on lesion detectability. Each object from each phantom scan was then segmented and placed randomly in a corresponding blank phantom image. The resulting individual images were presented blindly to seven physician observers (two nuclear medicine and five breast imaging radiologists) and scored in a binary fashion (1-correctly identified object, 0-incorrect). The sensitivity, specificity, and accuracy of lesion detectability were calculated and plots of sensitivity versus ACR and lesion diameters for different phantom thicknesses and count density were generated.

RESULTS

The overall (mean) detection sensitivity across all variables was 0.68 (95% CI: [0.64, 0.72]) with a corresponding specificity of 0.93 [0.87, 0.98], and diagnostic accuracy of 0.72 [0.70, 0.75]. The smallest detectable object varied strongly as a function of ACR, as sensitivity ranged from 0.36 [0.29, 0.44] for the smallest lesion size (3 mm) to 0.80 [0.75, 0.84] for the largest (14.5 mm).

CONCLUSIONS

The detectability performance of this PEM system demonstrated its ability to resolve small objects with low activity concentration ratios which may assist in the identification of early stage breast cancer. The results of this investigation can be used to correlate lesion detectability with tumor size, ACR, count rate, and breast thickness.

Comparison of diffusion-weighted MR imaging and FDG PET/CT to predict pathological complete response to neoadjuvant chemotherapy in patients with breast cancer

OBJECTIVE

To compare the use of diffusion-weighted MR imaging (DWI) and (18)F-FDG PET/CT to predict pathological complete response (pCR) in breast cancer patients receiving neoadjuvant chemotherapy.

METHODS

Thirty-four women with 34 invasive breast cancers underwent DWI and PET/CT before and after chemotherapy and before surgery. The percentage changes in the apparent diffusion coefficient (ADC) and the standardised uptake value (SUV) were calculated, and the diagnostic performances for predicting pCR were evaluated using receiver operating characteristic (ROC) curve analysis.

RESULTS

After surgery, 7/34 patients (20.6%) were found to have pCR. A( z ) values for DWI, PET/CT and the combined use of DWI and PET/CT were 0.910, 0.873 and 0.944, respectively. The best cut-offs for differentiating pCR from non-pCR were a 54.9% increase in the ADC and a 63.9% decrease in the SUV. DWI showed 100% (7/7) sensitivity and 70.4% (19/27) specificity and PET/CT showed 100% sensitivity and 77.8% (21/27) specificity. When DWI and PET/CT were combined, there was a trend towards improved specificity compared with DWI.

CONCLUSIONS

DWI and FDG PET/CT show similar diagnostic accuracy for predicting pCR to neoadjuvant chemotherapy in breast cancer patients. The combined use of DWI and FDG PET/CT has the potential to improve specificity in predicting pCR.

Initial clinical test of a breast-PET scanner

INTRODUCTION

The goal of this initial clinical study was to test a new positron emission/tomography imager and biopsy system (PEM/PET) in a small group of selected subjects to assess its clinical imaging capabilities. Specifically, the main task of this study is to determine whether the new system can successfully be used to produce images of known breast cancer and compare them to those acquired by standard techniques.

METHODS

The PEM/PET system consists of two pairs of rotating radiation detectors located beneath a patient table. The scanner has a spatial resolution of ∼2 mm in all three dimensions. The subjects consisted of five patients diagnosed with locally advanced breast cancer ranging in age from 40 to 55 years old scheduled for pre-treatment, conventional whole body PET imaging with F-18 Fluorodeoxyglucose (FDG). The primary lesions were at least 2 cm in diameter.

RESULTS

The images from the PEM/PET system demonstrated that this system is capable of identifying some lesions not visible in standard mammograms. Furthermore, while the relatively large lesions imaged in this study where all visualised by a standard whole body PET/CT scanner, some of the morphology of the tumours (ductal infiltration, for example) was better defined with the PEM/PET system. Significantly, these images were obtained immediately following a standard whole body PET scan.

CONCLUSIONS

The initial testing of the new PEM/PET system demonstrated that the new system is capable of producing good quality breast-PET images compared standard methods.

Molecular Imaging in Breast Cancer - Potential Future Aspects

SUMMARY: Molecular imaging aims to visualize and quantify biological, physiological, and pathological processes at cellular and molecular levels. Recently, molecular imaging has been introduced into breast cancer imaging. In this review, we will present a survey of the molecular imaging techniques that are either clinically available or are being introduced into clinical imaging. We will discuss nuclear imaging and multiparametric magnetic resonance imaging as well as the combined application of molecular imaging in the assessment of breast lesions. In addition, we will briefly discuss other evolving molecular imaging techniques, such as phosphorus magnetic resonance spectroscopic imaging and sodium imaging.

The assessment of breast cancer response to neoadjuvant chemotherapy: comparison of magnetic resonance imaging and 18F-fluorodeoxyglucose positron emission tomography

BACKGROUND

Neoadjuvant chemotherapy for locally advanced breast cancer is a widely accepted treatment. For assessment of the tumor response after chemotherapy, both magnetic resonance imaging (MRI) and (18)F-fluorodeoxyglucose positron emission tomography (PET) are promising methods.

PURPOSE

To retrospectively compare MRI and PET in the assessment of tumor response to neoadjuvant chemotherapy for primary breast cancer with the pathologic response as the reference standard.

MATERIAL AND METHODS

Between August 2006 and May 2008, 32 women with breast cancer underwent concurrent MRI and PET before and after neoadjuvant chemotherapy. For response assessment, we calculated the changes in the maximum diameters of the tumor (ΔD(max)) on MRI, and the changes in the standard uptake values (ΔSUV) on PET. The correlation between the ΔD(max) and ΔSUV was analyzed using Pearson's correlation coefficient. The correspondence rates between each imaging modality and pathologic assessment were calculated. For prediction of the pathologic complete response (pCR), the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were analyzed using the McNemar test.

RESULTS

The pathologic assessment of tumor response to neoadjuvant chemotherapy identified eight complete responses (25.0%), 10 partial responses (31.2%), and 14 non-responses (43.8%). The change in size on MRI was moderately correlated with the change in SUV on PET (r=0.574, p=0.001). The correspondence rate of response assessment was 75.0% (24/32) between MRI and pathologic response and 53.1% (17/32) between PET and pathologic response. For the pCR, specificity (95.8% vs. 62.5%) and PPV (83.3% vs. 47.1%) were statistically higher on MRI than PET (p < 0.05), while sensitivity (100.0% vs. 62.5%) and NPV (100.0% vs. 88.5%) on PET tended to be higher than MRI.

CONCLUSION

Before and after neoadjuvant chemotherapy for breast cancer, the ΔD(max) of MRI correlated moderately with the ΔSUV on PET. For prediction of the pCR, MRI proved to be a more specific modality than PET.

Positron emission tomography for benign and malignant disease

Functional imaging using radiolabeled probes that specifically bind and accumulate in target tissues has improved the sensitivity and specificity of conventional imaging. Fluorodeoxyglucose (FDG)-positron emission tomography (PET) has shown improved diagnostic accuracy in differentiating benign from malignant lesions in the setting of solitary pulmonary nodules. FDG-PET has become useful in preoperative staging of patients with lung cancer, and is being tested with many other malignancies for its ability to change patient management. This article provides an overview of the current status of FDG-PET and presents the challenges of moving toward routine use.

Positron emission mammography in breast cancer presurgical planning: comparisons with magnetic resonance imaging

PURPOSE

The objective of this study was to compare the performance characteristics of (18)F-fluorodeoxyglucose (FDG) positron emission mammography (PEM) with breast magnetic resonance imaging (MRI) as a presurgical imaging and planning option for index and ipsilateral lesions in patients with newly diagnosed, biopsy-proven breast cancer.

METHODS

Two hundred and eight women >25 years of age (median age = 59.7 ± 14.1 years) with biopsy-proven primary breast cancer enrolled in this prospective, single-site study. MRI, PEM, and whole-body positron emission tomography (WBPET) were conducted on each patient within 7 business days. PEM and WBPET images were acquired on the same day after intravenous administration of 370 MBq of FDG (median = 432.9 MBq). PEM and MRI images were blindly evaluated, compared with final surgical histopathology, and the sensitivity determined. Substudy analysis compared the sensitivity of PEM versus MRI in patients with different menopausal status, breast density, and use of hormone replacement therapy (HRT) as well as determination of performance characteristics for additional ipsilateral lesion detection.

RESULTS

Two hundred and eight patients enrolled in the study of which 87% (182/208) were analyzable. Of these analyzable patients, 26.4% (48/182), 7.1% (13/182), and 64.2% (120/182) were pre-, peri-, and postmenopausal, respectively, and 48.4% (88/182) had extremely or heterogeneously dense breast tissue, while 33.5% (61/182) had a history of HRT use. Ninety-two percent (167/182) underwent core biopsy for index lesion diagnosis. Invasive cancer was found in 77.5% (141/182), while ductal carcinoma in situ (DCIS) and/or Paget's disease were found in 22.5% (41/182) of patients. Both PEM and MRI had index lesion depiction sensitivity of 92.8% and both were significantly better than WBPET (67.9%, p < 0.001, McNemar's test). For index lesions, PEM and MRI had equivalent sensitivity of various tumors, categorized by tumor stage as well as similar invasive tumor size predictions with Spearman's correlation coefficient of 0.61 for both PEM and MRI compared to surgical pathology. Menopausal status, breast density, and HRT did not influence the sensitivity of PEM or MRI. For 67 additional unsuspected ipsilateral lesions or multifocal lesions, PEM had sensitivity of 85% (34/40) and specificity of 74%, (20/27) compared to MRI's sensitivity of 98% (39/40) and specificity of 48% (13/27) [p = 0.074, for sensitivity; p = 0.096 for specificity]

CONCLUSION

PEM is a good alternative to MRI as a presurgical breast imaging option and its performance characteristics are not affected by patient menopausal/hormonal status or breast density.

PET in women with high risk for breast or ovarian cancer

Data on the use of PET in women with genetic or familial high-risk for breast or ovarian cancer are scarce. Open issues include the complementary use of dedicated breast-PET scanners in patients at high-risk for breast cancer, the relation between pathological characteristics of cancer diagnosed in BRCA carriers and (18)F-fluorodeoxyglucose ((18)F-FDG)-avidity, and the predictive value of PET in patients at high-risk for ovarian cancer presenting with a pelvic mass or potential chemical markers. Therefore, the use of PET in high-risk patients with unproven malignant disease needs to be investigated in well designed clinical trials. Once breast or ovarian cancer is diagnosed, indications for (18)F-FDG-PET or PET-CT imaging are similar for high-risk patients and patients with sporadic cancer. However, PET can provide data that are beyond tumour detection per se. Future directions of PET in high-risk patients might include monitoring the response of BRCA carriers to new treatments such as poly-ADP ribose polymerase (PARP) inhibitors, personalisation of treatment, and the use of new PET tracers to investigate the tissue changes related to increased risk for breast and ovarian cancer.

[Diffusion-weighted MR imaging of the breast]

Diffusion-weighted imaging is helpful to further characterize lesions that remain indeterminate after morphological and dynamic MR evaluation. Suspicious lesions are hyperintense on diffusion-weighted images with corresponding low ADC values, indicating restricted diffusion and hypercellularity. Benign lesions and tumors responding to treatment usually have no diffusion restriction. ADC maps are useful for T2W hyperintense lesions that could mask the presence of restricted diffusion. Image fusion is sometimes needed to accurately localize enhancing lesions on ADC maps. For indeterminate lesions, a hypocellular appearance suggests a lower ACR category whereas the presence of restricted diffusion suggests a higher category.

Modern breast cancer detection: a technological review

Breast cancer is a serious threat worldwide and is the number two killer of women in the United States. The key to successful management is screening and early detection. What follows is a description of the state of the art in screening and detection for breast cancer as well as a discussion of new and emerging technologies. This paper aims to serve as a starting point for those who are not acquainted with this growing field.

Clinical imaging characteristics of the positron emission mammography camera: PEM Flex Solo II

We evaluated a commercial positron emission mammography (PEM) camera, the PEM Flex Solo II. This system comprises two 6 x 16.4 cm detectors that scan together covering up to a 24 x 16.4 cm field of view (FOV). There are no specific standards for testing this detector configuration. We performed several tests important to breast imaging, and we propose tests that should be included in standardized testing of PEM systems.

METHODS

We measured spatial resolution, uniformity, counting- rate linearity, recovery coefficients, and quantification accuracy using the system's software. Image linearity and coefficient of variation at the edge of the FOV were also characterized. Anecdotal examples of clinical patient data are presented.

RESULTS

The spatial resolution was 2.4 mm in full width at half maximum for image planes parallel to the detector faces. The background variability was approximately 5%, and quantification accuracy and recovery coefficients varied within the FOV. Positioning linearity began at approximately 13 mm from the edge of the detector housing. The coefficient of variation was significantly higher close to the edge of the FOV because of limited sensitivity in these image planes.

CONCLUSION

A reconstructed spatial resolution of 2.4 mm represented a significant improvement over conventional whole-body PET scanners and should reduce the lower threshold on lesion size and tracer uptake for detection in the breast. Limited-angle tomography and a lack of data corrections result in spatially variable quantitative results. PEM acquisition geometry limits sampling statistics at the chest-wall edge of the camera, resulting in high variance in that portion of the image. Example patient images demonstrate that lesions can be detected at the chest-wall edge despite variance artifacts, and fine structure is visualized routinely throughout the FOV in the focal plane. The PEM Flex camera should enable the functional imaging of breast cancer earlier in the disease process than whole-body PET.

Molecular PET/CT imaging-guided radiation therapy treatment planning

The role of positron emission tomography (PET) during the past decade has evolved rapidly from that of a pure research tool to a methodology of enormous clinical potential. (18)F-fluorodeoxyglucose (FDG)-PET is currently the most widely used probe in the diagnosis, staging, assessment of tumor response to treatment, and radiation therapy planning because metabolic changes generally precede the more conventionally measured parameter of change in tumor size. Data accumulated rapidly during the last decade, thus validating the efficacy of FDG imaging and many other tracers in a wide variety of malignant tumors with sensitivities and specificities often in the high 90 percentile range. As a result, PET/computed tomography (CT) had a significant impact on the management of patients because it obviated the need for further evaluation, guided further diagnostic procedures, and assisted in planning therapy for a considerable number of patients. On the other hand, the progress in radiation therapy technology has been enormous during the last two decades, now offering the possibility to plan highly conformal radiation dose distributions through the use of sophisticated beam targeting techniques such as intensity-modulated radiation therapy (IMRT) using tomotherapy, volumetric modulated arc therapy, and many other promising technologies for sculpted three-dimensional (3D) dose distribution. The foundation of molecular imaging-guided radiation therapy lies in the use of advanced imaging technology for improved definition of tumor target volumes, thus relating the absorbed dose information to image-based patient representations. This review documents technological advancements in the field concentrating on the conceptual role of molecular PET/CT imaging in radiation therapy treatment planning and related image processing issues with special emphasis on segmentation of medical images for the purpose of defining target volumes. There is still much more work to be done and many of the techniques reviewed are themselves not yet widely implemented in clinical settings.

Initial characterization of a dedicated breast PET/CT scanner during human imaging

We have constructed a dedicated breast PET/CT scanner capable of high-resolution functional and anatomic imaging. Here, we present an initial characterization of scanner performance during patient imaging.

METHODS

The system consisted of a lutetium oxyorthosilicate-based dual-planar head PET camera (crystal size, 3 x 3 x 20 mm) and 768-slice cone-beam CT. The position of the PET heads (separation and height) could be adjusted for varying breast dimensions. For scanning, the patient lay prone on a specialized bed and inserted a single pendent breast through an aperture in the table top. Compression of the breast as used in mammography is not required. PET and CT systems rotate in the coronal plane underneath the patient sequentially to collect fully tomographic datasets. PET images were reconstructed with the fully 3-dimensional maximum a posteriori method, and CT images were reconstructed with the Feldkamp algorithm, then spatially registered and fused for display. Phantom scans were obtained to assess the registration accuracy between PET and CT images and the influence of PET electronics and activity on CT image quality. We imaged 4 women with mammographic findings highly suggestive of breast cancer (breast imaging reporting and data system, category 5) in an ongoing clinical trial. Patients were injected with (18)F-FDG and imaged for 12.5 min per breast. From patient data, noise-equivalent counting rates and the singles-to-trues ratio (a surrogate for the randoms fraction) were calculated.

RESULTS

The average registration error between PET and CT images was 0.18 mm. PET electronics and activity did not significantly affect CT image quality. For the patient trial, biopsy-confirmed cancers were visualized on dedicated breast PET/CT on all patient scans, including the detection of ductal carcinoma in situ in 1 case. The singles-to-trues ratio was found to be inversely correlated with breast volume in the field of view, suggesting that larger breasts trend toward increased noise-equivalent counting rates for all other things equal.

CONCLUSION

Scanning of the uncompressed breast with dedicated breast PET/CT can accurately visualize suspected lesions in 3 dimensions.