MGC500

The MGC500 is a handheld mini gamma camera developed for localizing sentinel lymph nodes. It's used for pre-surgical and intra-operative lymphoscintigraphy to image sentinel lymph nodes. Applications include melanoma, breast cancer, head, and neck. Lymphoscintigraphy is an area of increasing utility in determining which lymph node basins serve the diseased tissue. The presence or absence of regional lymph node involvement determines the staging and treatment of many malignant tumors. Clinical uses such as superficial tumors can be easily imaged, especially mammary carcinoma (breast cancer) and malignant melanoma. Radioactive colloids administered by licensed technologist or physician 2-3 hours prior to imaging. RN drain through lymphatic system and pool at the first lymph node basin relative to the injection site. Nodes can be easily located with MGC pre-surgery, and skin marked accordingly. During surgery, MGC can be used to finalize location.

Before the MGC, the intraoperative tool was the Gamma Probe, which produces a tone and a count, but no image. Spatial resolution is poor, and it has trouble detecting nodes close to other nodes or injection sites. Operator skill (not moving too quickly) is important Faster and more direct localization of sentinel nodes, leading to shorter time in the OR, shorter anesthetic, less surgeon time, and minimized trauma for patients.

CdTe Technology:

While conventional gamma cameras consist of a scintillating crystal such as Sodium Iodide and photomultipler tubes, MGC500 incorporates a solid state semiconductor detector called Cadmium Telluride. CdTe allows the imaging device to be smaller, lighter, and more portable with higher spatial resolution and faster imaging capabilities.

Clinical Benefits:

The highly sensitive MGC500 can localize sentinel nodes in about 60 seconds, significantly reducing physician's assessment time. The MGC500 system is placed on a mobile cart, allowing it to be moved anywhere to capture images. Using a lightweight handheld camera allows physicians to image patients from any position, angle, or direction. MGC500 is useful in detecting sentinel nodes pre-operatively that are in close proximity to each other, near injection sites, weaker threshold nodes, or those in difficult locations. The ability to modify thresholds allows the detection of low threshold nodes (low up-take), which are typically difficult to detect. The MGC500 achieves high spatial resolution images with 1024 pixels and a pitch of 1.4mm. CdTe detectors cause less scattering, further enhancing image quality. MGC500 software has the energy window setting for up to 3 windows, which is considered useful to detect various kinds of radioisotopes at a time to create enhanced images.

Specifications:

Field of View: 4.5 x 4.5 cm (1.76 x 1.76 inches), beneficial in detecting small organs and lesions such as sentinel lymph nodes. Number of Pixels: 1024 pixels (32 x 32 matrix size); Pixel size: 1.4mm x 1.4mm; Energy Range: 60 -300 keV; Quick Measurements: Length, ROI, Time Activity Curve. General measurement feature for quantitative analysis; Detachable 10 mm collimator

Options:

20 mm collimator for higher resolution imaging; Flexible arm unit and detector holder

What is the MGC500?

The Mini Gamma Camera (MGC500) is a nuclear medical imager (commonly known as a scintillation or gamma camera) that is smaller, lighter and more portable than conventional gamma cameras. The MGC500 is intended for use in nuclear medicine procedures, mainly for intra-operative and pre-surgical lymphoscintigraphy. The MGC500 detects and visualizes gamma rays emitted from an administered radiopharmaceutical. While previous gamma cameras have consisted of a scintillating crystal such as a Sodium Iodide and photomultiplier tubes (PMT), the design of the MGC500 incorporates a solid-state CdTe semiconductor detector. This allows the imaging device to be smaller, lighter, and more portable with higher spatial resolution and faster imaging capabilities.

What is CdTe?

Cadmium Telluride is the solid-state semiconductor radiation detector produced by synthesizing Cadmium and Telluride. The absorption efficiency of CdTe is higher than other similar purposed detector materials to achieve a highly sensitive detector, and the semiconductor material used allows for the direct conversion from radiation energy to the electrical signals. CdTe delivers high sensitivity and high-energy resolution images in a smaller, lighter, and more portable imaging device.

Clinical Applications - Benefits

What are the MGC500 clinical benefits?

a)	The highly sensitive MGC500 can localize sentinel lymph nodes in about 60 seconds, significantly reducing physician's assessment time.
b)	The MGC500 system is placed on a mobile cart, allowing it to be easily moved anywhere to capture images.
c)	Using a handheld camera, patients can be imaged from any position, angle, or direction.
d)	The MGC500 is useful in detecting nodes pre-operatively that are in close proximity to each other, near injection sites, weaker threshold nodes, or nodes in deeper locations. The ability to modify thresholds allows the detection of low threshold nodes (low up-take), which are difficult to detect.
e)	The MGC500 achieves high spatial resolution images with 1024 pixels and a pitch of 1.4mm. CdTe detectors cause less scattering, further enhancing image quality.

What are the intended clinical uses?

Clinical uses include imaging of superficial tumors, especially mammary carcinoma (breast cancer) and malignant melanoma. Lymphoscintigraphy is an area of increasing utility to map the sentinel lymph nodes for biopsy to determine whether the tumor cells have spread (metastasized) to the lymph nodes. This procedure is important to determine the area to be removed during surgery as well as before and after surgery.

How is lymphoscintigraphy performed using the MGC500?

The procedure of lymphoscintigraphy using the MGC500 is basically similar to the gamma probe. Before going to the operating room, a small dose of radiopharmaceutical such as filtered Sulfer Colloid marked by a radioactive tracer called Technetium 99m is injected in the region of the patient's primary lesion of the tumor. It takes about 15 to 30 minutes for the Tc-99m to travel from the tumor region to the sentinel lymph nodes, where localization of the sentinel lymph nodes is performed with the conventional gamma camera and the nodes are mapped. On the same day or the following day after the injection, the sentinel lymph nodes are localized in combination with the MGC500 and the gamma probe to remove the sentinel nodes

What radiopharmaceuticals are used in sentinel lymph node mapping?

· Tc-99m filtered Sulfur Colloid
· Tc-99m human serum Albumin
· Tc-99m Albumin Colloid
· Tc-99m Sodium Pertechnetate
· Tc-99m Tin Colloid
· Tc-99m Phytic Acid

The typical injection amount for SLN procedure is 0.15-1 mCi. The amount of radioactivity that migrates to the sentinel or lymphatic nodes ranges from 1/100 to 1/1000.

Can the MGC500 identify sestamibi (Tc-99m sestamibi, Tc-99m-MIBI)?

Though the Tc-99m is the optimal radionuclide for the MGC500, sestamibi imaging depends on its application: which organ you would like to see and what is the activity. Tc-99m sestamibi is often used for thyroid and parathyroid imaging/uptake as well as myocardial perfusion and breast cancer imaging. According to the Society of Nuclear Medicine’s guidelines, the typical injection amount is 5-25mCi for parathyroid scintigraphy, for which the MGC500 should be applicable. Further clinical validations are expected with the MGC500.

What would happen if the MGC500’s maximum imaging count rate is saturated?

The maximum imaging count rate of the MGC500 is 250kcps or 250,000 counts per second and the imaging sensitivity is rated at 730cpm/uCi or 730 counts per minute per microcurie; however, those rates are not guaranteed under MGC500 specifications. When the activity is too high, the MGC500 will start to produce the wrong images due to an imaging pulse pile-up.

Is the MGC500 available for PET scan? What is the MGC500’s energy range?

No, the energy range of the MGC500 is from 60 to 300 keV (kilo electron volts), which is not suitable for 511keV PET agents.

Table: Properties of frequently/optimally used radionuclides for the MGC500

Nuclide	Name	Radiation Energy (gamma)	Half-life
Tc-99m	Technetium	141 keV	6 h
Ga-67	Gallium	93, 185, 300 keV	3.3 d
In-111	Indium	171, 245 keV	2.8 d
Tl-201	Thallium	167 keV	73 h
I-123	Iodine	159 keV	13.2 h

What are the benefits of MGC500 compared with a conventional gamma camera?

a)	MGC 500 is portable and mobile enough to bring in the operating room. The conventional gamma camera is a large fixed system requiring a dedicated room for patient imaging.
b)	The conventional gamma camera consists of a scintillating crystal such as a Sodium Iodide and photomultiplier tubes (PMT). These PMT's are comprised of large components limiting system resolution and speed, while the MGC500 utilizes the CdTe semiconductor detector with Tungsten collimator to achieve high spatial resolution of 1.4 mm and much faster acquisition times. This enables physicians to rapidly detect small, close, weak or deep sentinel lymph nodes or adjacent nodes.
c)	The highly sensitive MGC500 can localize sentinel lymph nodes generally in about 60 seconds. This not only shortens the assessment time but also enables localization of nodes with a limited or weak dose, as the radioactivity of the Tc-99m accumulated in the sentinel lymph nodes decreases over time (half-life of Tc-99m is 6 hours) after the injection. It sometimes becomes difficult to detect sentinel lymph nodes using gamma probes during the operation due to limited spatial resolution. In such cases, the MGC500 can be useful to localize the nodes visually.

What are the benefits of MGC500 compared with a gamma probe?

The main difference is that the MGC500 provides high-resolution visual images, while the gamma probes only provide audible tones. Gamma probes typically cannot localize sentinel lymph nodes close to injection sites or in close proximity to each other. If the sentinel nodes do not contain tumor cells, this may eliminate the need to remove additional lymph nodes in the axillary area. The MGC500 has 4.5cm x 4.5cm (1.76x1.76 inches) field of view, and can visualize multiple nodes simultaneously in some cases. Therefore, less invasive surgeries may be possible using the MGC 500 than just using gamma probes.

What is the difference for the correct diagnosis when compared with the blue dye method?

In a recent clinical study investigating early stage breast cancer, the detection rate of sentinel lymph nodes were reported at 76% using the blue dye method only, 92% with gamma probe, 91% with simultaneous use, and 93% with the addition of scintigraphy.

Can the MGC500 determine if lymph nodes are metastasized?

Not currently. The MGC500 software has a feature of drawing a time activity curve (TAC) with dynamic acquisition, so in the future, it may be possible.

What are the key features of the MGC500?

Mobility & Speed: The MGC500 provides high-resolution images in near real-time anywhere it's needed. Using a lightweight handheld camera allows patients to be imaged from any position, angle, or direction.

Field of View (FOV): The MGC500 has 4.5 x 4.5 cm (1.76 x 1.76 inches) FOV, beneficial in detecting small organs and lesions, such as sentinel lymph nodes. The image consists of 1024 pixels, which is 32 x 32 matrix size.

Energy Window Setting: MGC500 software has the energy window setting for up to three windows, which is considered to be useful to detect various kinds of radioisotopes at a time to create enhanced images. (The benefits in clinical use are not yet identified.)

Sound Indicator: Same principle as gamma probes.

DICOM 3.0 (Optional): The acquired images can be pushed and stored to/in the DICOM corresponding server.

Quick measurement (Length, ROI, TAC): The MGC500 software has a general measurement feature for quantitative analysis.

What developments are planned for the MGC500?

While utilizing the benefits of CdTe as a semiconductor detector, we are planning to enlarge the FOV (field of view or imaging area) for imaging areas such as the thyroid.