Detection of Sentinel Node in Breast Cancer: Pilot Study with the Imaging Probe

The commonly used gamma probes are easy to use but also give rough information when employed in radioisotope-guided surgery. When images are required for exact localization, a gamma camera as well as a probe have to be used. Position-sensitive photomultipliers have contemporaneously allowed high-resolution scintigraphy and miniaturization of gamma cameras. We have assembled a miniature gamma camera with a 1-square-inch field of view and an intrinsic resolution of about 1 mm. When the minicamera is collimated with a large-holed, highly sensitive collimator, it acquires a spatial resolution of 3 mm. This prototype has been tested in the detection of difficult-to-image breast cancer sentinel nodes. Five nodes that had not been found with the usual technique of an Anger camera plus conventional probe were checked with the miniature camera that we named imaging probe: it actually is small enough to be used as a probe and large enough to give an image. One of the five nodes was found and imaged. It was small, disease-free, close to the tumor and probably hidden by the Compton halo around the peritumoral injection site. Our pilot study shows that the imaging probe, although still a prototype, has certain advantages over conventional methods when lymph node localization is required during surgery.

Imaging performance comparison between a LaBr3: Ce scintillator based and a CdTe semiconductor based photon counting compact gamma camera

The authors report on the performance of two small field of view, compact gamma cameras working in single photon counting in planar imaging tests at 122 and 140 keV. The first camera is based on a LaBr3: Ce scintillator continuous crystal (49 x 49 x 5 mm3) assembled with a flat panel multianode photomultiplier tube with parallel readout. The second one belongs to the class of semiconductor hybrid pixel detectors, specifically, a CdTe pixel detector (14 x 14 x 1 mm3) with 256 x 256 square pixels and a pitch of 55 microm, read out by a CMOS single photon counting integrated circuit of the Medipix2 series. The scintillation camera was operated with selectable energy window while the CdTe camera was operated with a single low-energy detection threshold of about 20 keV, i.e., without energy discrimination. The detectors were coupled to pinhole or parallel-hole high-resolution collimators. The evaluation of their overall performance in basic imaging tasks is presented through measurements of their detection efficiency, intrinsic spatial resolution, noise, image SNR, and contrast recovery. The scintillation and CdTe cameras showed, respectively, detection efficiencies at 122 keV of 83% and 45%, intrinsic spatial resolutions of 0.9 mm and 75 microm, and total background noises of 40.5 and 1.6 cps. Imaging tests with high-resolution parallel-hole and pinhole collimators are also reported.

A 3D high-resolution gamma camera for radiopharmaceutical studies with small animals

The results of studies conducted with a small field of view tomographic gamma camera based on a Position Sensitive Photomultiplier Tube are reported. The system has been used for the evaluation of radiopharmaceuticals in small animals. Phantom studies have shown a spatial resolution of 2mm in planar and 2-3mm in tomographic imaging. Imaging studies in mice have been carried out both in 2D and 3D. Conventional radiopharmaceuticals have been used and the results have been compared with images from a clinically used system.

High-resolution scintimammography improves the accuracy of technetium-99m methoxyisobutylisonitrile scintimammography: use of a new dedicated gamma camera

The main disadvantage of technetium-99m methoxyisobutylisonitrile (MIBI) prone scintimammography is its limited sensitivity for T1a and T1b cancers with a size of less than 1 cm. We have developed a high-resolution scintimammographic technique using a gamma camera based on a new concept, namely a position-sensitive photo-multiplier tube. The field of view of this camera, previously known as the SPEM (single photon emission mammography) camera, was 10 cm diameter. Scintimammographic images were acquired in the axial view; each breast was compressed to a thickness of 3-6 cm, modal class 4 cm. When the compressed breast was larger than the field of view, more than one study was performed in order to image the entire gland. Fifty-three patients were studied with high-resolution-scintimammography (HRSM) and Anger camera prone scintimammography (ACPSM). HRSM was performed 70 min after i.v. administration of 740 Mbq of (99m)Tc-MIBI; ACPSM images were acquired 10 and 60 min following the injection. Early 10-min ACPSM images were only evaluated for routine diagnostic purposes, while comparison was carried out between the 60-min ACPSM and 70-min HRSM images. At fine-needle aspiration (FNA) and/or open biopsy, 31 patients showed cancer: 15 T1c, 11 T1b and 5 T1a. In T1a-T1b cancers, the sensitivity of scintimammography was 50% with ACPSM and 81.2% with HRSM (P<0.01). Specificity was 86% with both techniques. HRSM is a promising new technique that improves the sensitivity of (99m)Tc-MIBI scintimammography in tumours sized less than 1 cm without apparently reducing its specificity. We are now working on a larger field-of-view camera.

Role of 99mTc-Sestamibi scintimammography by SPEM camera in the management of breast cancer in the elderly

The incidence of breast cancer in the elderly is 10 fold higher than in the population younger than 65 years. Moreover, in this segment of the population there are not defined clear practice guidelines regarding patient management. X-ray mammography, the most widely used diagnostic technique, is often inadequate to differentiate benign from malignant lesions. 99mTc Sestamibi scintimammography plays an important role as complement to mammography; in fact it is a very sensitive and specific method for breast cancer detection, when cancers > 1 cm diameter are considered. However, sensitivity values fall to 50-60% in the case of small tumors (T1a and T1b). In this study we present the results of a new Small Field Of View (SFOV) Gamma Camera with very high spatial resolution that allows the first Single Photon Emission Mammography (SPEM). Eighteen patients aged 71 +/- 6 years with mammographically detected breast lesions were submitted to a Prone Scinti Mammography (PSM) by conventional Gamma Camera and to a SPEM on craniocaudal view. A final diagnosis was reached by histopathology. SPEM correctly diagnosed 15 of 16 cancers, while PSM was not able to recognize 5 malignant lesions with subcentimeter size. Both the techniques provided normal findings in the case of benign lesions. The 99mTc Sestamibi scintimammography, particularly when performed by SPEM camera, is a sensitive, specific, and non invasive method to define the nature of radiologically described breast masses and would be very useful as a complement to X-ray mammography in screening programs for breast cancer.

Single tube gamma camera for scintimammography

The development of large area Position Sensitive Photo Multiplier Tubes (PSPMT) by Hamamatsu is opening new imaging possibilities in Nuclear Medicine. In particular the realization of the 8" PSPMT prototype represents the first important technological advantage since the discovery of the Anger Camera. PSPMT virtually integrates in one hundreds PMT allowing the creation of dedicated detectors. A Single Tube Gamma Camera based on a 5" PSPMT dedicated to scintimammography is presented and discussed in this work. To optimize gamma camera response two different scintillating arrays were tested: YAP:Ce and CsI (Tl). Their overall size cover all photocathode active area, and crystal pixel size was 2 mm x 2 mm. The detection efficiency was comparable to that of Anger Camera. The best result was obtained by CsI (Tl) scintillating: an intrinsic spatial resolution of 1.6 mm FWHM and a relative energy resolution of 17% FWHM. New image possibilities in scintimammography are offered by Single Tube Gamma Camera operating in the same radiological projection of RX mammography.

The role of Compton background and breast compression on cancer detection in scintimammography

99mTc MIBI scintimammography is a promising diagnostic technique for cancer detection. Using a dedicated Small Field Of View Gamma Camera (SFOVGC) with the high spatial resolution recently developed, it is possible to improve the sensitivity and to achieve images in projections similar to mammography with the breast under moderate compression. This new technique is called Single Photon Emission Mammography (SPEM). Several factors affect the imaging of small cancers; breast thickness, tumor-collimator distance and body activity. A phantom study was performed to assess the role of breast compression in scintimammography. In this work we analyze the intensity and the energy distribution of Compton scattering affecting the breast scintigraphy, by a Germanium detector and by SFOVCG. Five patients with 7 to 18 mm sized cancer were studied. The intensity of Compton scattering resulted from 4 to 10 times greater than true events. The fundamental role played by breast compression to improve the scintimammographic sensitivity is discussed.

99mTc MIBI scintimammography with a high resolution single tube gamma camera: preliminary study

99mTc MIBI scintimammography is a sensitive and specific diagnostic technique for breast cancer detection when cancers more than 1 cm sized are considered. However the sensitivity falls in the case of submillimetric lesions. We developed a new Small Field of View, High Resolution Detector, able to image the breast in similar conditions of x-ray mammography: it allows the performance of Single Photon Emission Mammography (SPEM) studies. Seven patients with suspicion of malignant lesions were comparatively submitted to a Prone Scintimammography (PSM) by Anger camera and to a cranio-caudal view SPEM. The final diagnosis was reached by histopathology. Four malignant lesions were identified by SPEM but not by PSM, which that failed to image two submillimetric cancers. Both the cameras gave normal findings for benign lesions, confirming the high sensitivity of this technique. The results allow us to consider the SPEM camera as promising to improve scintimammographic sensitivity, even when small-sized tumors are examined.

99Tcm-MIBI uptake in green plants

Uptake of 99mTcm-sestamibi by biological structures depends on delivery and concentration by electrochemical gradients through the biological membranes and can be simply studied using a green plant model in which photosynthesis tightly modulates water and solute regional flow. Photosynthesis creates electrochemical gradients inside chloroplasts and mitochondria. Moreover, it is the driving force for the movement of water and solutes through induction of pore opening which causes capture of CO2 and loss of water vapour. Thus osmotic pressure increases thereby drawing water from the roots. Hypoestes sanguinolenta was used as an experimental model. This plant displays green zones (with several chloroplasts) and red zones (where they are absent). To detect the uptake differences between these zones we used a new, high-resolution gamma camera. Our results show that (a) 99mTcm-sestamibi is actively transported with water and ions by xylem to leaves where it may diffuse at cellular levels; (b) activation of photosynthesis by light strongly influences the total uptake and the selective compartmentation in green zones; and (c) the green plant's particular physiology tremendously enhances the differences between 99Tcm-sestamibi and 201Tl uptake. We suggest that viable cells, able to create and maintain electrochemical gradients, selectively take up 99Tcm-sestamibi.

Determination of x-ray spectra and of the scattered component up to 300 kV

Several x-ray spectra, including those of the ISO reference radiations, were measured by 2-hp Ge detectors. Measurements were carried out in different experimental conditions with regard to detector size, beam collimation, and SDD. A stripping procedure to improve the spectrum analysis was developed on the basis of a detailed evaluation (by means of a Monte Carlo method) of the detector's spurious effects. These effects include K-photon escape, Compton photon escape, electron escape, and collimation effect. The stripping procedure also allows us to determine directly the spectra of possible scattered radiation reaching the detector in addition to the primary beam. When the primary beam is heavily filtered, the leakage radiation from the x-ray tube housing scattered onto the detector may not be negligible even when the x-ray tube is provided with appreciable shielding. Possible practical consequence of these effects are discussed. The results obtained on the ISO x-ray spectra are in agreement with previous determinations. The advantage of the present procedure is its more immediate applicability to Ge detectors of any size and with different beam collimation conditions.

Diagnostic x-ray spectra measurements using a silicon surface barrier detector

A silicon surface barrier detector is used to analyse diagnostic x-ray spectra. This detector, usually employed to detect charged particles, has a very low efficiency for x-ray. This characteristic is advantageous in overcoming experimental problems caused by the high fluence rates typical of diagnostic x-ray beams. The pulse height distribution obtained with silicon surface barrier detectors is very different from the true photon spectra because of the presence of escaped Compton photons and the fact that detection efficiency falls abruptly when photon energy increases. A detailed analysis of the spurious effects involved in detection is made by applying a Monte Carlo method. A stripping procedure is described for implementation on a personal computer. The validity of this method is finally tested by comparison with the experimental results obtained with a Ge detector. The spectra obtained with the Si detector are in fairly good agreement with the analogous spectra measured with a Ge detector. The advantages of using Si as opposed to Ge detectors in x-ray spectrometry can be summarised as: its simplicity of use, its greater economy for use in routine diagnostic x-ray spectroscopy and the possibility that the stripping procedure can be implemented on a personal computer.

The radiation dose to the lens in radiology of the orbit

This paper describes research into measurement and reduction of the radiation dose to the lens during various examinations, namely skull and orbit, optic canal and optic strut, superior and inferior orbital fissure, localisation of foreign bodies in the eye, calcifications, orbital fractures, macrodacryography and orbital venography. Using rare-earth screens and high-sensitivity films, without an antiscattering grid, and with an added filtration of 0.5 mm Cu, it is possible to reduce the radiological risk during all investigations involving skull, orbit and eyeballs, while maintaining a good image quality. Particularly in those examinations with direct magnification (macrodacryography and venography, foreign bodies in the eye, orbital fractures), the dose to the lens is very low: less than 0.2 mGy/radiograph.

The use of cadmium telluride detectors for the qualitative analysis of diagnostic x-ray spectra

A method is introduced for the evaluation of x-ray spectra from x-ray machines operating in the range 50-100 kVp using a cadmium telluride (CdTe) detector with low detection efficiency. The pulse height distribution obtained with this kind of detector does not represent the true photon spectra owing to the presence of K-escape, Compton scattering, etc.; these effects were evaluated using a Monte Carlo method. A stripping procedure is described for implementation on a Univac 1100/82 computer. The validity of our method was finally tested by comparison with experimental results obtained with a Ge detector and with data from the literature; the results are in good agreement with published data.