Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Reexamination Certificate
1998-12-22
2001-05-15
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
C250S367000, C250S363020
Reexamination Certificate
active
06232605
ABSTRACT:
The invention relates to a flat scintillation gamma camera, with high spatial resolution, able to be assembled in modular fashion, as it is composed of blocks which can be adapted to each other to form gamma cameras of variable sizes and shapes, from a minimum of 2 single blocks to an unlimited number, in such a way as to constitute the first flat scintillation gamma camera, unlike flat ones operating, with semi-conductor detectors.
Its application can find employment is all fields of oncological diagnostics in general and in some cases of radioimmuno guided surgery. It is well known that one of the most widely used devices for the localization of tumours is the gamma camera which uses tracers concentrating where receiving structures behaving as tumour formations exist.
In oncological diagnostics the use of the Anger Camera is quite widespread, although it does not reach satisfactory values of spatial resolution in the evaluation and prevention of tumours.
The principle of the Anger Camera consists of the use of a number of photo-multiplier tubes (PMTs in a number usually exceeding 30) coupled through a glass window to a single Nal planar crystal.
The gamma radiation, interacting in the scintillating crystal, generates a light distribution whose centroid coincides with the interaction point of the photon. The PMTs, reading from the different positions the portion of light quantity generated by the event, convert it into an electrical signal. An appropriate average, operated through a resistive-capacity network, allows one to obtain two signals for the position x and y. The main limitations of the Anger Camera consist of a spatial resolution of at least 3 mm, for the dimensions of the photo tubes having a diameter of about 60 mm and dead zone present between the PMTs in the order of 5-7 mm, the non homogeneous response of the photo cathodes, the light distribution which in this case must be broader than the diameter of the PMTs. Having fixed as technological limit for the scintillation performance that of NaI(Tl), under these conditions the limit value of spatial resolution cannot be better than 3 mm.
Another critical point is the peripheral dead zone.
Because of the broad distribution of light, an event close to the edge of the camera undergoes great deformations in position if it occurs at a distance of less than 5 cm; this entails a considerable limitation in the use of this camera for limited fields and imaging small organs and in particular anatomic adaptation applications.
Due to the Pb shielding necessary for the gamma ray detection connected to the use of passive Pb or W collimators, the thickness of the camera entails heavy weights (tens of kg) which limit its mechanical positioning use through special support and motion systems.
Moreover the broad distribution of light with circular symmetry limits preferred shapes to the circular one.
The active area of the current gamma cameras has progressively grown over time according to the technological capability of constructing ever larger scintillating crystals.
To improve the spatial resolution of the gamma camera based on Anger's principle, it is necessary to reduce the FWHM (Full Width Half Maximum) light distribution. Associated thereto, a reduction in the sampling size of the light (diameter of the PMT photo multiplier) results. This entails a quadratic increase of the photo tubes (5 mm of sampling entails a hundred-fold increase in the number of PMTs). Unfortunately, due to the technological difficulties related to the construction of photo tubes, the active area/dead area ratio decreases with the diameter of the PMTs entailing the loss of large fractions of light and large position uncertainties between individual PMTs. Moreover, the gain alignment procedures for hundreds of PMTs are particularly onerous and costly, in addition to the costs intrinsic in hundreds of individual PMTs.
The interest originated in the past few years towards the development of gamma cameras with high spatial resolution inevitably leads to hopes in a precocious diagnosis of tumours by means of ever more accurate and sophisticated technologies. Already the development of apparatuses dedicated to certain pathologies (such as SPEM=Single Photon Emission Mammography and PEM=Positron Emission Mammography dedicated to the assessment of breast carcinoma) moves the problem to the construction of machines dedicated to specific clinical applications. One of the needs of the new oncological diagnostics remains in any case linked to the possibility of having available versatile equipment, able to reach high spatial resolutions, at reduced costs. Already PET (Positron Emission Tomography) in some ways is wholly innovative for equipment dedicated to specific neurological pathologies.
The present invention constitutes a modular type of instrument, able to be adapted to different types of oncological investigations and, for the first time in the state of the art, able to adapt its constructive shape to the anatomy of the human body. This type of gamma camera in fact revolutionizes the concept of classic gamma camera like the Anger camera, further adding a technology able to attain extremely high levels of spatial resolution (in the order of 1-2 mm).
The modularity of the device stems from the use of individual Position Sensitive Photo-Multiplier Tubes (PSPMT), which behave as individual blocks to be joined without limitation, ranging from a minimum of two individual blocks to a variable number, thus attaining total areas of detection of any dimension.
The dimensions of each individual block are roughly 22 mm×22 mm or less of active area, and total size of about 30 mm×30 mm or less. The length of the individual photo tubes is about 30 mm, so that the thickness of the entire block can be defined as nearly flat with respect to a gamma camera which, on the contrary, has considerable bulk. The crucial technological problem is the one pertaining to the so-called “dead zones”, i.e. the border zone between two photo tubes. Having solved this problem, using different technological solutions, individual blocks can be used to obtain different designs to be adapted to different requirements. The invention therefore constitutes the first scintillation gamma camera, of a flat type, to be used also according to differentiated sizes and at contained costs. In its simplest application variation it is possible to use just two blocks (about 3 cm×6 cm in area) for applications during surgical operations, or for external oncological diagnosis to detect small areas. An object of the invention, hence, is also the realization of an actual imaging system sensitive to gamma radiation, of variable dimensions, usable also for external diagnoses of turnouts of small dimensions (for instance skin melanomas, thyroid investigations, etc.). For instance, in order to remove a tumour surgically, the surgeon needs to localise it and, for that purpose, he/she normally uses the results obtained with the diagnostic systems employed to identify the tumour itself (radiography, CAT scans, NMR, Scintigraphy).
Such a technique can be replaced with the use of a standard gamma camera i.e. one having a single PSPMT which, although its dimensions are quite reduced, nonetheless still has considerable bulk during the surgical operation. Such information has a considerable advantage connected to the real-time display of any neoplastic formations and the confirmation of their total elimination after the surgical intervention for their removal.
Thus, the realisation is desirable of an actual imaging system sensitive to gamma radiations, of variable dimensions according to the different diagnostic needs, usable also for external diagnoses of tumours of small dimensions (for instance skin melanomas, thyroid examinations, etc.), since the reduced size, for example, can allow the total ease of handling of the device, with extremely reduced weight and the ability to visualize hard to reach areas of interest (between organs). Small detectors able to detect accumulations of radio
Pani Roberto
Soluri Alessandro
Browdy and Neimark
C.N.R. - Consiglio Nazionale Delle Ricerche
Gabor Otilia
Hannaher Constantine
LandOfFree
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