How does positron emission mammography work




















Imaging takes 10 minutes per view total of 40 minutes for a standard 4-view examination and usually starts at least one hour after injection of the radiotracer. The patient must be fasting for hours prior to the test and should rest quietly for about an hour after injection prior to imaging.

Benefits Breast PET is generally considered a diagnostic test used to determine the extent of cancer within the breasts, and can be used as an alternative to breast MRI for that purpose [1, 2].

Considerations Breast PET exposes the patient to a moderately high whole body radiation dose and is not used for screening [3]. Breast PET distinguishes cancer from silicone implant rupture. Left MLO mammogram left image, taken from the side of the breast in this year-old woman shows retroglandular silicone implant that has ruptured with extracapsular silicone obscuring most of the tissue.

A larger mass is noted just above the implant arrow. Final pathology revealed a 5. Community Healthcare Services CHS system 2-line horizontal solid 2 CHS Icon Search bariatrics behavioral cancer diagnostic heart neuro orthopedics womens childbirth classes doctor health fairs immediate care lectures locations remote access screenings services support groups weight management.

Back to Womens Diagnostic Center. The separation between the detector heads can be adjusted to match the thickness of the breast. The system uses position sensitive photomultiplier tubes PS-PMT that are optically coupled to the crystal blocks. The coordinates of the coincidence on opposing PS-PMT faces are decoded by the system electronics and corrected for spatial distortion and efficiency [ 17 ].

The images from this system are obtained by performing a limited-angle weighted-backprojection algorithm. This consists on dividing the image into several equidistant planes and backprojecting the lines or response LOR onto those planes. With this technique, the image plane closest to the site of the tumor has the most focused image, while all the other planes present more blurred images, as it can be seen in the schematic diagram of Figure 3.

This is known as the focal plane effect. Weighted backprojection used in the PEM-I scanner. From [ 18 ]. The complete system has a spatial resolution of 2.

It is estimated that the system is not able to detect tumors with a tumor-to-background ratio lower than [ 20 ]. The smallest cancerous lesion detected with PEM-I was 1. The lower value of sensitivity with PEM, with respect to mammography, was due, according to the authors, to the small FOV of the PEM device and to the impossibility of imaging tumors localized close to the chest wall less than 2 cm. These limitations are related to the PMTs used, whose useful field of view is significantly smaller than its area, preventing imaging near their edges.

Figure 4 shows a typical set of images obtained with PEM-I, each image corresponding to a plane of the sample, with a visible site of FDG uptake in a region close to the chest wall [ 19 ]. A typical set of images obtained with the PEM-I scanner. Each image corresponds to a plane, with the leftmost image corresponding to the image plane closer to the upper detector. A visible site of FDG uptake can be seen in a region close to the chest wall.

From [ 19 ]. This way, emission and transmission scans can be obtained. Data acquisition is performed by moving the detectors along a linear path, in order to image as much breast as possible. The PEM detectors translation allows to image an area equal to the entire X-ray field of view [ 23 ].

The system can also work separately from the mammography unit, allowing closer chest wall access. From [ 22 ]. For each segment of the scan, list mode data are acquired, histogrammed and reconstructed by backprojection.

This allows the operator to view partial images during the scan acquisition. At the end of the entire scan, the complete list mode data are reconstructed using a maximum-likelihood expectation-maximization algorithm. The intrinsic spatial resolution of the system is 1. The image resolution is 2. The timing window used was 9 ns. The clinical trials performed so far [ 24 , 25 ] were all performed on patients with known breast cancer or suspected lesions. Hence, they provide little information on the specificity of the technique.

In one of these studies [ 25 ], PEM was able to visualize 39 out of 44 lesions. The non visualized lesions ranged in size from a 1 mm ductal carcinoma in situ DCIS to a 1 cm infiltrating ductal carcinoma. Some lesions could not be visualized due to limitations on how posterior the breast tissue is observable by the device. Others, as interpreted by the authors of the study, due to the variability in the metabolic activity of breast cancer cells, similarly to what happens with whole body PET.

From [ 25 ]. An example of such a case can be seen in Figure 6. This preliminary clinical trial seems to indicate that the technology is promising and worthy of further investigation.

An image of the scanner mounted on the biopsy table, together with a torso phantom can be seen in Figure 7. The PEM detector heads, mounted in a biopsy table, are highlighted by the black arrows. A torso phantom can be seen in the table. From [ 27 ]. Since one of the goals of the system is to perform PEM guided biopsies, a trigonometric algorithm was developed to determine the lesion stereotactic coordinates. PEM images acquired in a single detector position were initially reconstructed using a weighted backprojection algorithm similar to the used for the PEM-I system described above, or by a limited angle tomography scheme [ 23 ].

The described acquisition scenario was compared with multiple acquisitions between the same limiting angles, at small uniform increments [ 29 ]. The results were somehow mixed, with no clear evidence of significant advantage of one acquisition scenario over the other, although less artifacts were observed with the multiple angle acquisition.

This lead to a study of the complete angular sampling around the breast [ 30 ] through step and shoot acquisitions. Not surprisingly, this study showed that the complete angular sampling provided better image quality with respect to a single acquisition with stationary detectors.

The study also revealed some of the weaknesses of the system, such as the low rate acquisition capability and the lack of DOI information. This system has four planar detector heads that can rotate around the breast. The initial clinical studies have shown the ability of the system to detect lesions also detected by standard methods [ 32 ]. Another system was developed at the Jefferson Laboratory and Duke University to image the compressed breast [ 33 ]. This system is used mounted on an X-ray mammography unit, although the PEM detector heads must be removed to acquire the X-ray image.

The distance between the detector heads can be adjusted to match the size of the breast. Image reconstruction is performed by means of the backprojection scheme. The image spatial resolution varied from 4. An image of the system can be seen in Figure 8. The PEM detectors are highlighted by black arrows. From [ 34 ]. A pilot clinical trial was performed using this system [ 34 ]. This trial included 23 patients with suspected breast malignancies.

Therefore, it does not provide meaningful information concerning the specificity of the technique. In this study, where the majority of the evaluated lesions had diameters smaller than 2. The size of the three malignant lesions that PEM was unable to detect varied from 8 mm to 15 mm. The system was able to detect a 4 mm DCIS that was not detected by mammography. The use of the optical fiber allows the exact match between the crystal area and the active PMT dimensions, thus avoiding gaps between detector modules.

It also provides better imaging close to the chest wall, since the plates are active out to the edge of the field-of-view. The main disadvantage of the fiber-optic coupling is the loss of scintillation light. The two detector plates can be mounted in a gantry allowing variable plates separation, detector plates rotation and angular motion.

Based on Monte Carlo simulation, the expected intrinsic spatial resolution of the scanner was about 2. A prototype of this system was assembled but, to our knowledge, no clinical test were ever performed. A second prototype of this detector was build, with modified geometry and electronics. The integration of this system with a dedicated CT system was exploited [ 37 ].

By Open Medscience Apr 26, Positron emission mammography imaging — PEM The diagnostic breast imaging tool Positron Emission Mammography PEM uses short-lived positron-emitting isotopes to generate high-resolution tomographic images of cancer within the breast.

PEM breast imaging Positron Emission Mammography is currently part of the diagnostic toolkit to help assess patients that had detectable abnormalities in their mammogram. The indications for PEM include: the initial staging evaluation of patients with diagnosed cancer; distinguishing recurrent carcinoma from scar tissue; monitoring response to chemotherapy treatment PEM has high imaging sensitivity for breast lesions.

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