Background: Molecular breast imaging (MBI) is a novel breast imaging technique that uses Cadmium Zinc
Telluride (CZT) gamma cameras to detect the uptake of Tc-99m sestamibi in breast tumors. Current
techniques employ an administered dose of 20-30 mCi Tc-99m, delivering an effective dose of 6.5-10 mSv
to the body. This is ~ 5-10 times that of mammography. The goal of this study was to reduce the radiation
dose by a factor of 5-10, while maintaining image quality. Methods: A total of 4 dose reduction schemes
were evaluated - a) optimized collimation, b) improved utilization of the energy spectrum below the
photopeak, c) adaptive geometric mean algorithm developed for combination of images from opposing
detectors, and d) non local means filtering (NLMF) for noise reduction and image enhancement. Validation
of the various schemes was performed using a breast phantom containing a variety of tumors and containing
activity matched to that observed in clinical studies. Results: Development of tungsten collimators with
holes matched to the CZT pixels yielded a 2.1-2.9 gain in system sensitivity. Improved utilization of the
energy spectra yielded a 1.5-2.0 gain in sensitivity. Development of a modified geometric mean algorithm
yielded a 1.4 reduction in image noise, while retaining contrast. Images of the breast phantom demonstrated
that a factor of 5 reduction in dose was achieved. Additional refinements to the NLMF should enable an
additional factor of 2 reduction in dose. Conclusion: Significant dose reduction in MBI to levels comparable
to mammography can be achieved while maintaining image quality.
In women with radiographically dense breasts, the sensitivity of mammography is less than 50%. With the increase in the percent of women with dense breasts, it is important to look at alternative screening techniques for this population. This article reviews the strengths and weaknesses of current imaging techniques and focuses on recent developments in semiconductor-based gamma camera systems that offer significant improvements in image quality over that achievable with single-crystal sodium iodide systems. We have developed a technique known as Molecular Breast Imaging (MBI) using small field of view Cadmium Zinc Telluride (CZT) gamma cameras that permits the breast to be imaged in a similar manner to mammography, using light pain-free compression. Computer simulations and experimental studies have shown that use of low-energy high sensitivity collimation coupled with the excellent energy resolution and intrinsic spatial resolution of CZT detectors provides optimum image quality for the detection of small breast lesions. Preliminary clinical studies with a prototype dual-detector system have demonstrated that Molecular Breast Imaging has a sensitivity of ~90% for the detection of breast tumors less than 10 mm in diameter. By comparison, conventional scintimammography only achieves a sensitivity of 50% in the detection of lesions < 10 mm. Because Molecular Breast Imaging is not affected by breast density, this technique may offer an important adjunct to mammography in the evaluation of women with dense breast parenchyma.
Variations in blood volume in the myocardium through the cardiac cycle have previously been considered constant. More recent studies have indicated a considerably variation from end diastole to end systole. These studies were nearly all performed under non-physiological conditions using muscle preparations or ex situ cardiac preparations. This study was designed to assess the dynamic changes of the intramyocardial blood volume in the intact animal under normal flow conditions using single photon emission computed tomography (SPECT). Radiolabeled, 15 micrometers diameter, microspheres were emoblized in the myocardial microcirculation of dogs with subsequent scans in a TRIAD single-photon-emission-computed- tomography scanner. Gated images were obtained at 63 msec intervals encompassing the entire heart. Transmural voxel (equals volume element) brightness was measured in all tomographic images reflecting global and regional count density in the myocardium. There was a significant decrease in the blood volume from end diastole to end systole (10.8 cc/100 mL muscle volume; p < 0.00001). The decrease from diastole (ED) to systole (ES) in image brightness at the apex, mid ventricle, and base were: -5.7% (p < 0.01, apex vs. base), -4.7% (p < 0.01, mid ventricle vs. base) and +2.2%, respectively. Conclusions: (1) respiratory and ECG gated SPECT images allow measurement of intramyocardial blood volume changes throughout the cardiac cycle in the intact animal; (2) myocardial blood content is maximum at ED; (3) these findings progressively diminished in magnitude from apex to base.