Stereotaxy

Information about Stereotaxy

The introduction of screening by mammography has led to the detection of a considerable number of non-palpable abnormal lesions. Most of them, typically, are benign, and regular follow-up may be sufficient. But some are indeterminate or suspicious and require further investigation. Biospy is playing a key role in breast cancer detection and has improved considerably breastcare.

What is a Biopsy?

What is a Biopsy?

A biopsy involves removing a sample of tissue for diagnostic histological examination. It is a preferred method for determining whether a tumour is benign or malignant.
When the lesions are visible with ultrasound this technique is preferred. In the case of an impalpable radiological abnormality, the stereotactic mammography must be used – particularly in the presence of microcalcifications.


What is Stereotaxy?

Stereotaxy is a process that determines the position of a lesion in 3 dimensional space (X, Y and Z coordinates) using a stereotactic pair of X-ray images. The biopsy puncture is then made at this precise spot with millimetric accuracy.


Schema stereotaxy

The first image is obtained with the tube arm in the 0° position, perpendicular to arm in the 0° position, perpendicular to Y coordinates 2 dimensions.
When an image of the same lesion is obtained with the arm at a different angle with respect to the detector, the lesion appears to move along a line, called the epipolar line.
This distance is determined by the depth of the lesion within the breast ie the Z axis. Stereotaxy uses a pair of images obtained by tilting the tube arm +15° and -15° perpendicular to the image detector.
By measuring the position of the lesion on the stereotactic pair, it is possible to calculate its position in each of the 3D detector (X, Y, Z axes).


Types of Stereotactic Biopsy


Fine-needle cytopuncture

This technique may be adequate for the diagnosis of palpable breast cancers. For non-palpable lesions, some studies have revealed its limitations, as insufficient material is obtained for a reliable diagnosis. Moreover it gives inadequate results in the diagnosis of microcalcifications or for pre-operative grading.


Microbiopsy

In the 90s, in order to reduce the uncertainties linked to the insufficient quantities of material obtained with fine-needle cytopuncture, biopsy techniques using small-calibre equipment (21G to 16G) were developed. They made it possible to achieve better sensitivity in the diagnosis of malignant lesions (60 to 92%). The use of automatic biopsy guns has improved the quality of samples and provides good diagnostic results for opacities. However, studies have shown that sensitivity is still inadequate for microcalcifications. Microbiopsy is still indicated for the detection of lymph node involvement, or abnormal nodes on ultrasound. However an experienced cytologist is required as part of the diagnostic team.


Macrobiopsy

In their constant search for greater sensitivity, doctors have progressively turned to the use of a 14G needle (removing approximately 17 mg of tissue) to obtain larger samples. Diagnostic sensitivity for malignant lesions is between 85 and 95%, and specificity is close to 100%, with however some inadequacies in the presence of microcalcifications.


Vacuum-assisted macrobiopsy

With this technique, and using stereotactic guidance, it is possible to obtain large cylindrical tissue samples thanks to vacuum assistance. The various guns available on the market use 14G, 11G or 8G needles (providing samples of 35mg, 100mg and 300mg respectively). They considerably reduce the number of false negatives and may be used to completely remove some lesions, thereby avoiding surgical intervention.
Alongside the progress made in the tools (gun and needles) used to obtain samples, these techniques have all undoubtedly benefited from the advent of digital stereotaxy systems which improve the accuracy of localization of lesions and the feasibility of the procedure. Stereotactic biopsy has thus become a genuine alternative to a diagnostic surgical biopsy.


The Successive Generations of Digital Stereotaxy Systems

Stereotactic localizing systems have evolved enormously over the last few years, and various techniques are now available to allow practitioners to carry out these biopsy procedures:


1st-Generation Systems

  • 3 Dimension targeting systems linked to an analogue device.


Developed in the 90s, these systems enabled stereotaxy to position itself as an alternative to a diagnostic surgical biopsy. They possessed the following characteristics:

  • The stereotactic module associated with the device can be removed after the procedure
  • The patient usually is in a sitting position
  • Stereotactic positioning is carried out using a CCD camera.


2nd-Generation Systems

At the end of the 90s, in order to avoid problems of syncope and patient movement due to the sitting position, some manufacturers proposed another solution: the dedicated digital table.


Its specifications are as follows:

  • The table is fixed and used solely for stereotaxy
  • The patient lies on her stomach (in a prone position)
  • The tube and the digital plate are situated below the table on which the patient is lying. X-rays are detected on a phosphorus plate and the image is relayed by optical fibres to the CCD camera.


Latest Generation of Systems

In order to respond to the needs of those who wish to practice high quality stereotaxy and overcome some limitations of current systems (Image quality access to posterior lesions, cost…) , GE Healthcare, in collaboration with leading specialists, has invented a new approach: the Senographe DS Interventional with its dedicated table.

The Senographe DS Interventional can be used for all types of biopsy, with or without vacuum assistance and for preoperative position marking.