Digital Breast Tomosynthesis (DBT). The Method's principles, advantages and limitations

Ioannis K. Giannakelos, RT

Mammography is a specialized technique of medical imaging, which, through the use of a low energy X-ray system, aims at the early detection and diagnosis of diseases such as breast cancer. In fact, mammography is a radiography of the breast. Its main and primary goal is to detect breast cancer before the display of relevant symptoms or palpation of tumors. Mammography represents a measurement that : i) allow early detection of breast cancer with the distant aim of reducing mortality and the use of improved therapeutic techniques aims, ii) the radial charge of the examinant is not significantly valuable, iii) give back comparable results.

A mammogram cannot approve with certainty that the presence of a lesion is an element of a malignancy. But it can provide with useful information on the need for further investigation of the problem through the use of other techniques such as ultrasonography (Ultrasounds) and displaying with Magnetic Tuning (Magnetic Resonance Imaging). The two types of breast lesions that can be detected in a mammogram are calcifications and masses.

Breast compression is essential for the following reasons:

a) To stretch the breast tissue so as to reduce the possibility even the smallest lesions to be hidden from underlying tissues.

b) In order to be able to reduce the dose, as we would like to depict a tissue of a smaller thickness.

c) Compression immobilizes the breast and thus the motion artifacts in the final image can be minimized.

d) The Compression reduce X-ray scattering, that results in increase of the image sharpness.

Diagnostic mammography is commonly used to evaluate a patient with abnormal clinical findings such as for example a bump in the breast or an alteration of the teat.

Some of the benefits-benefits of mammography are the following:

·  The basic advantage is the early detection and diagnosis of breast cancer, which in turn has a very significant impact on prognosis.

·  Breast imaging greatly improves the ability of the doctor to detect small tumors that cannot be detected by palpation. This fact offers the possibility of choice through different therapeutic techniques so that the best possible outcome for the patient can be achieved.

·  The use of mammography also improves greatly the ability to detect small lesions in tissues which are confined to the milk ducts within the breast. Such a malformation is called porous carcinoma in situ (ductal in situ carcinoma - DCIS). These tumors are important to be removed when they are at an early stage and this can only be achieved after their detection with the help of mammography.

·  Improved early-stage treatment: Improving treatment options is one of the most important benefits of early detection of breast cancer. Early detection, in turn, leads to a reduced number of mastectomies and consequently to better aesthetic results, reduced chemotherapy use, and reduced invasive biopsies commonly performed in the armpit area.

To the disadvantages of the method we can summarized:

a) Use of ionizing radiation

b) Falsehood positive evidence.

c) Hyper diagnosis

The tomosynthesis systems are based on digital mammography, which are able to produce both 2D images and 3D tomosynthesis images. The 2D images and the tomosynthesis can be taken individually or in combination by exerting parallel pressure on the breast.

In order to obtain the reconfiguration images, the lamp rotates in the form of an arc, drawing a series of low-dose images from different angles across the breast. The images are then reconstructed into very thin sections from 0.5 mm to 1 mm.

The superiority of this diagnostic test against digital mammography (2D) is attributed to increased detection of cancer cases in women with dense breasts. Specifically, this technique offers higher sensitivity in breast cancer diagnosis and detect lesions with 2D would escape since it would be overlapping with the inflated elements of dense parenchyma. The possibility of this, to reflect and analyze the tissues that they show up with each other, is also due to the reduction in the rate for women with dense breasts in preventive population control programs.

Studies have shown that tomosynthesis prevails over 2D mammography for the characterization of lesions not accompanied by micro-calcifications. Are more clearly depicted in dense breasts the limits of the mass, the density, the number of lesions and other accompanying findings such as displaced and vessels.

As a preventive control tool is important to consider the radiation dose. Dose recording from 2D image acquisition and synthesis is approximately 2.5mGy. This dose is less than the 3mGy allowed by the Mammography Quality Standards Act.

Companies try to improve the quality of the images they are composing. When this is achieved, double 2D and image tomography will be avoided and their use will be suitable for study and comparison with previous digital mammograms.

The time needed to interpret the synthesis is an additional factor to be considered. Most studies indicate that the time required to read the test is about twice as great as 2D.

The workstation is only used to interpret the examinations. For long-term storage of images, 2D images and tomosynthesis images are sent to a permanent storage system called PACS. All sections of the synthesis are sent to the PACS for storage, from which they can be retrieved at any time for future display on the workstation. The electronic storage space required for a reconfiguration test is approximately 100 times greater than the capacity required for a 2D mammogram.

According with the carrier Mammography Quality Standards Act. (MQSA) for the use of this new technology and familiarity interpretation of images by radio diagnostician required 8-hour training. Similar training time is also required for radiological technologists.

Digital tomosynthesis is a method for reconstructing tomographic images of a limited arc (Limited angle reconstruction of tomographic images), which are produced at variable heights, based on a beam of angular projections. Particularly in breast imaging, studies including clinical cases have shown that digital tomosynthesis can provide much superior image quality compared to that of conventional mammography images. In this method, the illustrated volume (volume) is reconstructed from two-dimensional projections in order to provide three dimensional information about the structure of the patient anatomy. The most basic algorithms that are used for reconstruction are back-up and the method of displacement and addition. However, these algorithms lead to the appearance of significant image ambiguity caused by other structures that are not at the level of interest. This leads to poor traceability of objects within the level we focus on. Digital breast transplantation is a female breast imaging technique that is offered either as a separate system or as a choice in the existing two-dimensional mammography systems. During the acquisition of the images, the X-ray tube moves by deleting a small angle around the breast, and in this way a series of images is taken. The movement of the tube can be continuous or with a shape of step and shoot.

Image quality and performance of digital breast tomosynthesis are determined by:

·  The X-ray tube

·  The detector

·  The quality of the package

·  The dose

·  The image reconstruction method

·  The movement that may exist during the acquisition of images

·  The geometry of the system

The ability to detect lesions in this technique is influenced by three key issues:

1. The quality that the representation of the corruption in the reconstructed image plan can have.

2. The ability of the digital tomosynthesis system to suppress the texture that is outside the image plane and is produced by adjacent tissues.

3. The thickness of the reconstructed plan presented to the radiologist.

The application of tomosynthesis is gaining ground in the breast imaging. Study results argue that when proper attention is paid to image acquisition, the interpretation of examination, storage, radiologist training, radiation dose, then the use of tomosynthesis in our clinical practice can actually offer positive results.

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