An easy Z-score imaging system for discrimination between very early Alzheimer's disease and controls using brain perfusion SPECT in a multicentre study

BACKGROUND AND AIM: In Alzheimer's disease (AD), regional cerebral blood flow (rCBF) in the posterior cingulate gyrus and precuneus has been reported to decrease even at a very early stage. We performed a multicentre SPECT study to evaluate the discrimination ability of an easy Z-score imaging system (eZIS) by detecting an rCBF decrease in this area with a common normal database between very early AD patients at the stage of mild cognitive impairment and age-matched healthy volunteers. METHODS: Brain perfusion SPECT images of 40 Alzheimer's disease patients and 40 healthy volunteers were acquired from four gamma camera systems in different institutions. Systematic differences of SPECT images between different gamma cameras were corrected using conversion maps calculated from the SPECT images of the same brain phantom. Ten observers with various degrees of expertise graded eZIS results for receiver operating characteristic (ROC) curves. ROC curves for a positive Z-score in the volume of interest (VOI) of the posterior cingulate gyrus and precuneus were also analysed. RESULTS: An area under the ROC curve value (AZ) for ten observers showed the highest value of 0.866 on average with the smallest standard deviation of 0.027 in the condition of the lower threshold of a Z-score map of 2 without superimposition of VOI. Automated analysis of a Z-score in the VOI showed an AZ value of 0.895. CONCLUSION: Since the degree of expertise of the observers with respect to reading eZIS did not influence the performance and an eZIS can use a common normal database by converting site-specific SPECT data to the core data, the eZIS was considered to be very useful for diagnosing early AD in routine studies in many institutions.     

Automated discrimination between very early Alzheimer disease and controls using an easy Z-score imaging system for multicenter brain perfusion single-photon emission tomography

BACKGROUND AND PURPOSE: In Alzheimer disease (AD), a peculiar regional cerebral blood flow (rCBF) abnormality has been reported in the posterior cingulate gyri and precunei, even at a very early stage. We performed a multicenter brain perfusion single-photon emission tomography (SPECT) study to evaluate the discrimination ability of an easy Z-score imaging system (eZIS) with a common normal data base between patients with very early AD at the stage of mild cognitive impairment and age-matched healthy controls. MATERIALS AND METHODS: For a multicenter study, SPECT images of 40 patients with AD and 40 healthy volunteers were acquired from 4 gamma camera systems in 4 different institutions. Systematic differences of SPECT images between gamma cameras were corrected by using conversion maps calculated from the SPECT images of the same brain phantom. Receiver operating characteristic (ROC) analysis was performed to discriminate patients and controls by using a Z-score in the volume of interest (VOI), which had been defined as a region related to AD in subjects other than those in a multicenter study. RESULTS: Bilateral posterior cingulate gyri, precunei, and parietal cortices were defined as a VOI showing rCBF reduction in very early AD. A new indicator of rCBF abnormality in the VOI provided 86% accuracy for distinction of AD and healthy controls in the multicenter study. The area under the ROC curve was 0.934. CONCLUSION: Because an eZIS can use a common normal data base by converting site-specific SPECT data to the core data, the eZIS was useful for automated diagnosis of very early AD in routine studies in multiple institutions.     

Simulation study on a stationary data acquisition SPECT system with multi-pinhole collimators attached to a triple-head gamma camera system

Objectives

The aim of the study was to develop a new SPECT system that makes it possible to acquire projection data stationary using a triple-head gamma camera system.

Methods

We evaluated several data acquisition geometry with multi-pinhole collimators attached to a triple-head gamma camera system. The number of pinholes for each camera was three to twelve, and we located these holes on collimator plates adequately. These collimator holes were tilted by predefined angles to efficiently cover the field of view of the data acquisition system. Acquired data were reconstructed with the OS-EM method. In the simulations, we used a three-dimensional point source phantom, brain phantom, and myocardial phantom. Attenuation correction was conducted with the x-ray CT image of the corresponding slice.

Results

Reconstructed images of the point source phantom showed that the spatial resolution could be improved with the small number of pinholes. On the other hand, reconstructed images of the brain phantom showed that the large number of pinholes yielded images with less artifact. The results of the simulations with the myocardial phantom showed that more than eight pinholes could yield an accurate distribution of activity when the source was distributed only in the myocardium.

Conclusions

The results of the simulations confirmed that more than eight pinholes for each detector were required to reconstruct an artifact free image in the triple-head SPECT system for imaging of brain and myocardium.     

Dynamic sequence respiratory gated perfusion pulmonary SPECT without external tracking device

Objective

The purpose of this study was to develop and evaluate a new method for respiratory gated pulmonary perfusion SPECT (RGPS) based on dynamic acquisition without using an external tracking device (ETD) or list-mode data acquisition.

Methods

In the phantom study, our method used a dynamic sequence technique, which was specified by sequences of 50-ms acquisition during 30 s per view of SPECT instead of using an ETD. For this purpose, we created a computer program that identified respiratory phases by calculating the center of activity (COA) in each dynamic frame image. We compared RGPS using the dynamic sequence acquisition (RGPS-DS) and RGPS using ETD (RGPS-ETD) in phantom studies employing a cylinder phantom filled with technetium-99m solution attached to an instrument providing a simple harmonic motion. In the patient study, RGPS-DS was applied to data collected from 3 patients during a routine study of Tc-MAA pulmonary perfusion SPECT.

Results

In the phantom study, the calculation of COA indicated a good agreement between RGPS-DS and RGPS-ETD. With an oscillatory phantom movement amplitude of 30 mm, the amplitudes determined by RGPS-DS and RGPS-ETD (28.36 and 27.58 mm, respectively) were identical on considering a pixel size of 4.66 mm for reconstructed SPECT images. In the patient study, applicability of our method to patient data was demonstrated.

Conclusions

We have showed the feasibility of our method to obtain RGPS without ETD, and conclude that RGPS-DS may be an innovative and efficient technique in respiratory gated pulmonary perfusion SPECT. Further studies with a larger number of patients should demonstrate the accuracy of our method.     

Performance of a semiconductor SPECT system: comparison with a conventional Anger-type SPECT instrument

Objective

The performance of a new single photon emission computed tomography (SPECT) scanner with a cadmium-zinc-telluride (CZT) solid-state semiconductor detector (Discovery NM 530c; D530c) was evaluated and compared to a conventional Anger-type SPECT with a dual-detector camera (Infinia).

Methods

Three different phantom studies were performed. Full width at half maximum (FWHM) was measured using line sources placed at different locations in a cylindrical phantom. Uniformity was measured using cylindrical phantoms with 3 different diameters (80, 120, and 160 mm). Spatial resolution was evaluated using hot-rod phantoms of various diameters (5, 9, 13, 16, and 20 mm). Three different myocardial phantom studies were also performed, acquiring projection data with and without defects, and evaluating the interference of liver and gallbladder radioactivity. In a clinical study, the D530c employed list-mode raw data acquisition with electrocardiogram (ECG)-gated acquisition over a 10-min period. From the 10-min projection data, 1-, 3-, 5-, 7- and 10-min SPECT images were reconstructed.

Results

The FWHM of the D503c was 1.73–3.48 mm (without water) and 3.88–6.64 mm (with water), whereas the FWHM of the Infinia was 8.17–12.63 mm (without water) and 15.48–16.28 mm (with water). Non-uniformity was larger for the D530c than for the Infinia. Truncation artifacts were also observed with the D530c in a Φ160 mm phantom. The contrast ratio, as defined by myocardial defect/non-defect ratio, was better for the D530c than for the Infinia, and the influence from liver and gallbladder radioactivities was less. Quantitative gated SPECT (QGS) software demonstrated significant differences between data captured over a 10-min period, relative to those acquired over periods of <5 min; there was no difference between ejection fractions calculated using data capture for periods ≥5 min (p < 0.05).

Conclusions

The D530c is superior to the Infinia, with regard to both spatial resolution and sensitivity. In this study, these advantages were confirmed by the myocardial phantom and in a clinical setting, using the QGS software.     

Planar radionuclide angiography with a dedicated cardiac SPECT camera

Background

We compared a dedicated cardiac camera with a traditional system for left ventricular (LV) functional measurements using gated blood-pool imaging.

Methods

24-frame gated planar images were obtained from 48 patients in an LAO orientation for 6M counts/view on a standard gamma camera. Immediately thereafter, 24-frame ECG-gated data were obtained for 8 minutes on a dedicated cardiac SPECT camera. The gated SPECT image volumes were iteratively reconstructed and then transferred offline. In-house software was used to reproject the images into a 24-frame gated planar format. Both the original and the reprojected gated planar datasets were analyzed using semiautomated software to determine ejection fraction (EF), ventricular volume (end diastolic volume, EDV), peak ejection rate (PER), and peak filling rate (PFR).

Results

The difference in EF values averaged 0.4% ± 4.4%. The correlation in EF was r ≥ 0.94 (P < .01) with a linear regression slope of 0.98. Correlation of the EDV was r ≥ 0.86 (P < .01), but the volumes from the dedicated cardiac camera were smaller (linear regression slope was 0.6). Correlation of PFR and PER were r = 0.91 and r ≥ 0.83, respectively (P < .01 for both).

Conclusions

Reprojection of 24-frame gated blood-pool SPECT images is an effective means of obtaining LV functional measurements with a dedicated cardiac SPECT camera using standard 2D-planar analysis tools.     

Implementation of GPU accelerated SPECT reconstruction with Monte Carlo-based scatter correction

Objective

Statistical SPECT reconstruction can be very time-consuming especially when compensations for collimator and detector response, attenuation, and scatter are included in the reconstruction. This work proposes an accelerated SPECT reconstruction algorithm based on graphics processing unit (GPU) processing.

Methods

Ordered subset expectation maximization (OSEM) algorithm with CT-based attenuation modelling, depth-dependent Gaussian convolution-based collimator-detector response modelling, and Monte Carlo-based scatter compensation was implemented using OpenCL. The OpenCL implementation was compared against the existing multi-threaded OSEM implementation running on a central processing unit (CPU) in terms of scatter-to-primary ratios, standardized uptake values (SUVs), and processing speed using mathematical phantoms and clinical multi-bed bone SPECT/CT studies.

Results

The difference in scatter-to-primary ratios, visual appearance, and SUVs between GPU and CPU implementations was minor. On the other hand, at its best, the GPU implementation was noticed to be 24 times faster than the multi-threaded CPU version on a normal 128?×?128 matrix size 3 bed bone SPECT/CT data set when compensations for collimator and detector response, attenuation, and scatter were included.

Conclusions

GPU SPECT reconstructions show great promise as an every day clinical reconstruction tool.

     

Ultrafast nuclear myocardial perfusion imaging on a new gamma camera with semiconductor detector technique: first clinical validation

Purpose

To assess the diagnostic performance of a novel ultrafast cardiac gamma camera with cadmium-zinc-telluride (CZT) solid-state semiconductor detectors for nuclear myocardial perfusion imaging (MPI).

Methods

The study group comprised 75 consecutive patients (55 men, BMI range 19–45 kg/m²) who underwent a 1-day ^99mTc-tetrofosmin adenosine-stress/rest imaging protocol. Scanning was performed first on a conventional dual-detector SPECT gamma camera (Ventri, GE Healthcare) with a 15-min acquisition time each for stress and rest. All scans were immediately repeated on an ultrafast CZT camera (Discovery 530 NMc, GE Healthcare) with a 3-min scan time for stress and a 2-min scan time for rest. Clinical agreement (normal, ischaemia, scar) between CZT and SPECT was assessed for each patient and for each coronary territory using SPECT MPI as the reference standard. Segmental myocardial tracer uptake values (percent of maximum) using a 20-segment model and left ventricular ejection fraction (EF) values obtained using CZT were compared with those obtained using conventional SPECT by intraclass correlation and by calculating Bland-Altman limits of agreement.

Results

There was excellent clinical agreement between CZT and conventional SPECT on a per-patient basis (96.0%) and on a per-vessel territory basis (96.4%) as shown by a highly significant correlation between segmental tracer uptake values (r=0.901, p<0.001). Similarly, EF values for both scanners were highly correlated (r=0.976, p<0.001) with narrow Bland-Altman limits of agreement (?5.5–10.6%).

Conclusion

The novel CZT camera allows a more than fivefold reduction in scan time and provides clinical information equivalent to conventional standard SPECT MPI.     

A new method for evaluation of mild traumatic brain injury with neuropsychological impairment using statistical imaging analysis for Tc-ECD SPECT

Objective

The objective of this study was to identify specific brain lesions with regional perfusion abnormalities possibly associated with neuropsychological impairments (NPI), as sequela after mild traumatic brain injury (MTBI), using 99mTc-ethylcysteinate dimer single photon emission computed tomography (Tc-99m ECD SPECT) and its novel analytic software.

Methods

We studied 23 patients with diffuse axonal injury with NPI group (Impaired-DAI), 26 with MTBI with NPI group (Impaired-MTBI) and 24 with MTBI without NPI group (Healthy-MTBI). In each subject, Tc-99m ECD SPECT images were analyzed by easy Z score imaging system (eZIS) and voxel-based stereotactic extraction estimation (vbSEE). Segmented into lobule levels, ROIs were set in 140 areas in whole brain, and relative regional low Tc-99m ECD uptake was computed as “extent” (rate of coordinates with Z score >2.0 in the ROI). Receiver operating characteristic analysis was performed using “extent” to discriminate the three groups.

Results

The highest area under the curve (AUC) value for data of Impaired-DAI and Healthy-MTBI groups was obtained in ROI on the left anterior cingulate gyrus (LtACG), with AUC of 0.93, optimal “extent” cutoff value of 10.9 %, sensitivity 87.0 %, specificity 83.3 %. The highest AUC value for data of Impaired-MTBI and Healthy-MTBI groups was also in the LtACG, with AUC of 0.87, optimal “extent” cutoff value of 9.2 %, sensitivity 73.1 %, specificity 83.3 %.

Conclusions

Using two analytic software packages, eZIS and vbSEE, we identified specific lesions with low regional Tc-99m ECD uptake possibly associated with NPIs after MTBI. Especially, this trend was most marked in the left anterior cingulate gyrus in MTBI patients with NPIs and those with DAI. The optimal “extent” cutoff value, as a criterion for SPECT abnormality, might help the diagnosis of NPIs after MTBI.     

Gated tomographic radionuclide angiography using cadmium-zinc-telluride detector gamma camera; comparison to traditional gamma cameras

Purpose

Estimation of left ventricular ejection fraction (LVEF) with equilibrium 99MTc-HSA equilibrium radionuclide angiography (MUGA) is frequently used for assessing cardiac function. The purpose of this study was to compare intra- and interobserver variation between three different gamma cameras.

Materials and Methods

Eighty-two patients, scanned in the same sequential order on the three cameras. Each acquisition was analyzed twice by two technologists. Inter- and intraobserver variations were calculated as the coefficient of variation and the 95% confidence interval for limits of agreement between each sequence of analyses for each of the three cameras.

Results

The lowest intraobserver variations in LVEF for the two NaI-detector cameras were 3.1% (?4.0% to 3.5%) for the planar and 3.4% (?4.2% to 4.5%) for SPECT (P ≤ 0.001-0.019), the highest result for the CZT SPECT camera was 2.6% (?2.9% to 3.1%). Similarly, interobserver variation was 4.8% (?4.8% to 6.4%) and 4.9% (?5.4% to 7.5%), respectively, for each of the NaI-detector cameras and 3.3% (?3.4% to 4.3%) for the CZT SPECT camera (P ≤ 0.001-0.008).

Discussion

The CZT detector camera was superior to both NaI detector cameras regarding intra- and interobserver variation. The CZT SPECT camera may identify changes in LVEF with greater certainty than its NaI detector-equipped counterparts.     

Comparative study of anatomical normalization errors in SPM and 3D-SSP using digital brain phantom

Objective  

In single photon emission computed tomography (SPECT) cerebral blood flow studies, two major algorithms are widely used statistical parametric mapping (SPM) and three-dimensional stereotactic surface projections (3D-SSP). The aim of this study is to compare an SPM algorithm-based easy Z score imaging system (eZIS) and a 3D-SSP system in the errors of anatomical standardization using 3D-digital brain phantom images.     

Comparing slow- versus high-speed CT for attenuation correction of cardiac SPECT perfusion studies

Background

For SPECT, CT-based attenuation correction is preferred. Many different models of CT are available with SPECT/CT systems. Our study compares clinical cardiac SPECT images that were attenuation corrected using slow-rotation CT and high-speed CT transmission scans.

Methods

We evaluated 59 rest/stress perfusion studies from patients who had undergone both a SPECT/CT with a slow-rotation CT and a perfusion study on a PET/CT camera equipped with a high-speed CT scanner. Each SPECT study was reconstructed with transmission maps from both CT scans and the relative perfusion was assessed using semi-automated software. The summed stress/rest/and difference scores (SSS/SRS/SDS) were compared as well as the test classification.

Results

The intraclass correlation coefficients for the SSS, SRS, and SDS were 0.97, 0.96, and 0.80 respectively. There were no significant differences in the mean SSS, SRS, or SDS with the use of either CT for attenuation corrections. Classifying SSS?>?3 as abnormal, there was 97% concordance (???=?0.88). Classifying SDS?>?1 as abnormal, there was 95% concordance (???=?0.54). A McNemar??s test showed no significant differences.

Conclusions

There were no significant differences between using a high-speed CT and using a slow-rotation CT for attenuation correction of SPECT myocardial perfusion images.     

Comparative analysis of iterative reconstruction algorithms with resolution recovery for cardiac SPECT studies. A multi-center phantom study

Background

This investigation used image data generated by a physical phantom over a wide range of count statistics to evaluate the effectiveness of several of the newer commercially available SPECT reconstruction iterative algorithms (IRR) in improving perfusion defect contrast and spatial resolution, while controlling image noise.

Methods

A cardiac phantom was imaged using four different gamma cameras over a wide range of counts statistics (from 6 to 0.8 Mcounts). Images were reconstructed with FBP, OSEM, and the IRR available on site. IRR were applied without corrections (IRR NC), with attenuation correction (IRR AC), scatter correction (IRR SC), and attenuation + scatter corrections (IRR SCAC). Four image performance indices related to spatial resolution, contrast, and image noise were analyzed.

Results

IRR NC always determined significant improvements in all indices in comparison to FBP or OSEM. Improvements were emphasized with IRR SC and IRR SCAC. Count reduction from 6 to 1.5 Mcounts did not impair the performances of any of the considered indices.

Conclusions

This is the first study comparing the relative performance of different, commercially available, IRR software, over a wide range of count statistics; the additional effect of scatter and attenuation corrections, alone or in combination, was also evaluated. Our results confirm that IRR algorithms produce substantial benefits with respect to conventional FBP or OSEM reconstruction methods, as assessed through different figures of merit, in particular when SC and/or SCAC are also included.     

Aperture correction with an asymmetrically trimmed Gaussian weight in SPECT with a fan-beam collimator

Objectives

The aim of the study is to improve the spatial resolution of SPECT images acquired with a fan-beam collimator.

Methods

The aperture angle of a hole in the fan-beam collimator depends on the position of the collimator. To correct the aperture effect in an iterative image reconstruction, an asymmetrically trimmed Gaussian weight was used for a model. To confirm the validity of our method, point source phantoms and brain phantom were used in the simulation, and we applied the method to the clinical data.

Results

The results of the simulation showed that the spatial resolution of point sources improved from about 6 to 2 pixels full width at half maximum, and the corrected point sources were isotropic. The results of the simulation with the brain phantom showed that our proposed method could improve the spatial resolution of the phantom, and our method was effective for different fan-beam collimators with different focal lengths. The results of clinical data showed that the quality of the reconstructed image was improved with our proposed method.

Conclusions

Our proposed aperture correction method with the asymmetrically trimmed Gaussian weighting function was effective in improving the spatial resolution of SPECT images acquired with the fan-beam collimator.     

Evaluation of simultaneous 201Tl/99mTc dual-isotope cardiac SPECT imaging with model-based crosstalk compensation using canine studies

Background

Simultaneous ²⁰¹Tl/^99mTc-sestamibi dual-isotope myocardial perfusion SPECT imaging can reduce imaging time and produce perfectly registered rest/stress images. However, crosstalk from ^99mTc into ²⁰¹Tl images can significantly reduce ²⁰¹Tl image quality. We have developed a model-based compensation (MBC) method to compensate for this crosstalk. The method has previously been validated with phantom and simulation studies. In this study, we evaluated the MBC method using a canine model.

Methods

Left anterior descending or left circumflex coronary artery stenoses were created in 50 adult mongrel dogs weighing 20-30 kg. The dogs were injected with 111 MBq (3 mCi) of ²⁰¹Tl at rest, and a SPECT study acquired. Stress was induced by administering adenosine to the dog, followed by injection of 740 MBq (20 mCi) of ^99mTc-sestamibi at peak stress. A second SPECT study was performed with data acquired in both ²⁰¹Tl and ^99mTc energy windows to provide simultaneous dual-isotope projection data. The images were reconstructed using the ordered-subsets expectation-maximization reconstruction algorithm with compensation for attenuation, scatter, and detector response. For simultaneously acquired ²⁰¹Tl data, we also applied the MBC method to compensate for crosstalk contamination from ^99mTc.

Results

Without compensation, ^99mTc crosstalk increased the estimated ²⁰¹Tl activity concentration in the rest images and reduced defect contrast. After MBC, the ²⁰¹Tl images were in good agreement with the registered single-isotope images and ex vivo count data. The ischemic (IS) to non-ischemic (NIS) region ²⁰¹Tl activity concentration ratios were computed for single-isotope and dual-isotope studies. The correlation with ex vivo IS-NIS ratios was 0.815 after MBC, compared to the 0.495 from data without compensation. In addition, the regression line for the IS-NIS ratios with MBC was almost parallel to the line of identity with a slope of 0.93, compared to a slope of 0.45 without compensation.

Conclusions

These results demonstrate that model-based crosstalk compensation can provide substantial reduction of crosstalk effects in simultaneously acquired myocardial perfusion SPECT images in living biological systems.     

eZIS在脑血流灌注SPECT诊断神经退行性痴呆中的临床应用

简易Z评分成像系统（eZIS）是一种基于统计参数图和三维立体定向表面投影的辅助脑血流灌注SPECT图像自动诊断的统计分析方法,可以用于痴呆、帕金森病、共济失调和运动神经元病等神经系统疾病的诊断。与其他计算机辅助分析方法相比,eZIS可提供正常数据库,并通过图像转换程序实现不同机构的数据共享,使未来多中心、大样本量的临床研究成为可能。笔者就eZIS在脑血流灌注SPECT诊断神经退行性痴呆中的临床应用进行综述,旨在提高临床医师对eZIS的认识,促进其在临床及科研工作中的应用。     

First demonstration of 3-D lymphatic mapping in breast cancer using freehand SPECT

Purpose

Freehand SPECT is a 3-D tomographic imaging modality based on data acquisition with a hand-held detector that is moved freely, in contrast to conventional, fixed gamma camera systems. In this pilot study, the feasibility of freehand SPECT for 3-D lymphatic mapping in breast cancer was evaluated.

Methods

A total of 85 patients (age: 29–88 years) with an initial diagnosis of invasive breast cancer and no clinical evidence of nodal involvement prospectively underwent sentinel lymph node (SLN) biopsy. Preoperative lymphatic mapping (35–87 MBq ^99mTc-Nanocoll) included tomographic imaging with a SPECT/CT device (Siemens Symbia T6) serving as reference. Initially, the freehand SPECT approach was assessed in a pilot study consisting of 50 patients. The quality of each freehand SPECT acquisition was assessed and ranked as good, intermediate or poor. In another series comprising a further 35 patients (validation study), a guidance system for the acquisition was implemented based on the results of the pilot study, ensuring acquisitions with good quality. For 3-D tomographic image reconstruction, ad hoc models and iterative reconstruction algorithms were used in all 85 patients. To allow for adequate comparison, SPECT/CT data and freehand SPECT data were registered within the same coordinate system.

Results

In the pilot study, freehand SPECT enabled mapping of 24 of 83 SLNs in 20 of 44 patients (3 dropouts, 3 patients without SLN either in SPECT/CT or in freehand SPECT). Using SPECT/CT as reference, the accuracy of freehand SPECT was 77.8% (7/9 nodes) in scans with good quality, while for intermediate and poor quality scans, the accuracy was reduced to 34.3 and 12.8%, respectively. In the validation study, quality feedback improved the results significantly and freehand SPECT enabled the mapping of at least one SLN in 87.5% of the patients (28/32 ? 3 dropouts). Compared to the reference method, freehand SPECT showed a sensitivity of 83.3% (35/42 nodes). False-negative findings were related to insufficient scanning time, insufficient coverage of the axillary region, close proximity of the SLN to the injection site and low tracer uptake in the SLNs.

Conclusion

In this preliminary study, we could demonstrate that 3-D localization of SLNs is feasible using freehand SPECT technology. Prerequisites for acquisition of a good scan quality, most likely allowing precise SLN mapping, have been defined. This approach has high potential to allow image-guided biopsy and further standardization of SLN dissection, thus bringing 3-D nuclear imaging into the operating room.     

Evaluation of a multicrystal gamma camera and rotating chair for tomographic studies of the heart

Background

This study evaluates the feasibility of performing tomographic studies with a multicrystal gamma camera combined with a rotating chair.

Methods and Results

Tomographic acquisitions were performed with a cardiac phantom containing eight defects of different sizes. Defect size was determined from the fraction of counts in the short-axis slices that fell below a fixed threshold value. Image contrast was determined from the ratio of minimum/maximum counts. Images of an American College of Nuclear Physicians cardiac single-photon emission computed tomographic phantom were acquired and the results were compared with those obtained from 194 centers in the United States. For cardiac studies with ²⁰¹TI and ^99mTc, threshold values of 65% to 70% gave the best correlation (R ²>0.94) between true and measured defect sizes, although the slope of the regression line was less than 0.95 for both isotopes. Small inferior defects demonstrated poor image contrast, particularly for ^99mTc. Of the three defects in the American College of Nuclear Physicians phantom, the two largest were identified in the tomographic images.

Conclusions

A multicrystal gamma camera system coupled with a rotating chair can be used for tomographic studies of the heart. Image quality is poorer than that seen on conventional single-photon emission computed tomographic systems, particularly for ^99mTc.     

Concomitant radio- and fluorescence-guided sentinel lymph node biopsy in squamous cell carcinoma of the oral cavity using ICG-99mTc-nanocolloid

Purpose

For oral cavity malignancies, sentinel lymph node (SLN) mapping is performed by injecting a radiocolloid around the primary tumour followed by lymphoscintigraphy. Surgically, SLNs can then be localized using a handheld gamma ray detection probe. The aim of this study was to evaluate the added value of intraoperative fluorescence imaging to the conventional radioguided procedure. For this we used indocyanine green (ICG)‐^99mTc‐nanocolloid, a hybrid tracer that is both radioactive and fluorescent.

Methods

Fourteen patients with oral cavity squamous cell carcinoma were peritumourally injected with ICG-^99mTc-nanocolloid. SLNs were preoperatively identified with lymphoscintigraphy followed by single photon emission computed tomography (SPECT)/CT for anatomical localization. During surgery, SLNs were detected with a handheld gamma ray detection probe and a handheld near-infrared fluorescence camera. Pre-incision and post-excision imaging with a portable gamma camera was performed to confirm complete removal of all SLNs.

Results

SLNs were preoperatively identified using the radioactive signature of ICG-^99mTc-nanocolloid. Intraoperatively, 43 SLNs could be localized and excised with combined radio- and fluorescence guidance. Additionally, in four patients, an SLN located close to the primary injection site (in three patients this SLN was located in level I) could only be intraoperatively localized using fluorescence imaging. Pathological analysis of the SLNs revealed a metastasis in one patient.

Conclusion

Combined preoperative SLN identification and intraoperative radio- and fluorescence guidance during SLN biopsies for oral cavity cancer proved feasible using ICG-^99mTc-nanocolloid. The addition of fluorescence imaging was shown to be of particular value when SLNs were located in close proximity to the primary tumour.