Clinical Instrumentation

business loans Merchant Cash Advances Short Term Loads SBA Loans Long Term Loans Equipment Financing Big Lines of Credit best business loans Working Capital Small Business Loans

Gamma Probes:

1) RAIU probe

            It is used to quantify the uptake of a radiotracer, usually 131I or 123I in the thyroid gland  at 2, 6, 24 and 48 h. This type of device comprises a detector head associated with a scale meter. The detector consists of a crystal of sodium iodide activated with thallium [INa (Tl)] coupled to a photomultiplier. It has a collimator-type cylindrical or conical, with a single hole. The scaler has a multichannel analyzer that can be adjusted (the energy sector window) to choose the energy range to be measured. With this configuration, the radiation emitted by the thyroid gland is captured by the detector and converted into electrical pulses in the analyzer. It is necessary to measure the neck, background (counting the thigh). Subtracting the background from the neck, and comparing with a standard solution, measured in the same geometric conditions gives the percentage of uptake for the thyroid.

2) Gamma probe for radioguided surgery.

            Gamma probes are used to localize  radiotracer tissue concentrations in th operating room. The most common applications are for detection of sentinel lymphonodes in breast cancer and melanoma and also radioguided surgery of parathyroid tumors. Likewise, localize skeletal metastasis for biopsy is another interesting application.

            Intraoperative detection probes consist of a collimated detector crystal connected to a scale meter. Some probes have crystals of INa (Tl, activated), which possess a photomultiplier tube interposed between it and the scale meter. Others have bismuth germanate crystals (BGO), which do not require the photomultiplier. In this way the detector head is more stable and can be reduced in size, of paramount important if you eventually want to use this technology in laparoscopic surgery.

            For optimum utilization of this methodology it is crucial to build a detector with good spatial and temporal resolution. They will depend on the collimation, external shield of the detector, energy resolution and energy window setting. The operator has three different methods to detect the presence of radioactivity in the field of view: a record of counts per minute, an audible signal and light. These parameters indicate the surgeon with a reference position on the tissue to be removed, facilitating the dissection of surrounding tissue. The presence of nearby tissues with radioactive accumulation makes this procedure not so accurate, since the photons scattered from the site of unwanted concentration, interferes with the tissue to be extracted. It is a convenient procedure to scan the patient with the gamma camera 1 h to 2 h before the surgery and mark in the skin the projection of the lesion in anterior and lateral planar views. This is of great help for the surgeon to speed up the localization of the target. Usually the radionuclide employed is 99mTc. It is even possible to use 18F as a bone seeking agent or with FDG, but due to the high photon energy, the counts coming from adyacent tissues may make it more difficult an accurate detection.

            Recently some innovations are being proposed to improve intraoperative devices. One of them is to add a small squared detector and the possibility to get images on a monitor, not possible up until now. Another one has a mobile sliding detector, similar to an ultrasound transducer, that can detect photons from different angles and reconstruct tomographic images.

Page 2    Home       Index      Clinical Nuclear Medicine       Therapeutic Methods      Previous Page        Next   Page