Effects of iterative reconstruction on image contrast and lesion detection in gamma camera coincidence imaging in lung and breast cancers

Comparison of ordered-subset expectation maximization and filtered back projection reconstruction based on quantitative outcome from dynamic [18F]NaF PET images

[18F]NaF PET imaging is a useful tool for measuring regional bone metabolism. However, due to tracer in urine, [18F]NaF PET images of the hip reconstructed using filtered back projection (FBP) frequently show streaking artifacts in slices through the bladder leading to noisy time-activity curves unsuitable for quantification. This study compares differences between quantitative outcomes at the hip derived from images reconstructed using the FBP and ordered-subset expectation maximization (OSEM) methods. Dynamic [18F]NaF PET data at the hip for four postmenopausal women were reconstructed using FBP and nine variations of the OSEM algorithm (all combinations of 1, 5, 15 iterations and 10, 15, 21 subsets). Seven volumes of interest were placed in the hip. Bone metabolism was measured using standardized uptake values, Patlak analysis (Ki-PAT) and Hawkins model Ki-4k. Percentage differences between the standardized uptake values and Ki values from FBP and OSEM images were assessed. OSEM images appeared visually smoother and without the streaking artifacts seen with FBP. However, due to loss of counts, they failed to recover the quantitative values in VOIs close to the bladder, including the femoral head and femoral neck. This was consistent for all quantification methods. Volumes of interest farther from the bladder or larger and receiving greater counts showed good convergence with 5 iterations and 21 subsets. For VOIs close to the bladder, including the femoral neck and femoral head, 15 iterations and 10, 15 or 21 subsets were not enough to obtain OSEM images suitable for measuring bone metabolism and showed no improvement compared to FBP.

Determining the Performance of Fluorescence Molecular Imaging Devices Using Traceable Working Standards With SI Units of Radiance

To date, no emerging preclinical or clinical near-infrared fluorescence (NIRF) imaging devices for noninvasive and/or surgical guidance have their performances validated on working standards with SI units of radiance that enable comparison or quantitative quality assurance. In this work, we developed and deployed a methodology to calibrate a stable, solid phantom for emission radiance with International System of Units (SI) units of mW ·sr(-1) ·cm(-2) for use in characterizing the measurement sensitivity of ICCD and IsCMOS detection, signal-to-noise ratio, and contrast. In addition, at calibrated radiances, we assess transverse and lateral resolution of ICCD and IsCMOS camera systems. The methodology allowed demonstration of superior SNR of the ICCD over the IsCMOS technology and superior resolution of the IsCMOS over the ICCD approach. Contrast depended upon the camera settings (binning and integration time) and gain of intensifier. Finally, because the architecture of CMOS and CCD camera systems results in vastly different performance, we comment on the utility of these technologies for small animal imaging as well as clinical applications for noninvasive and surgical guidance.

A matter of collection and detection for intraoperative and noninvasive near-infrared fluorescence molecular imaging: to see or not to see?

PURPOSE

Although fluorescence molecular imaging is rapidly evolving as a new combinational drug/device technology platform for molecularly guided surgery and noninvasive imaging, there remains no performance standards for efficient translation of "first-in-humans" fluorescent imaging agents using these devices.

METHODS

The authors employed a stable, solid phantom designed to exaggerate the confounding effects of tissue light scattering and to mimic low concentrations (nM-pM) of near-infrared fluorescent dyes expected clinically for molecular imaging in order to evaluate and compare the commonly used charge coupled device (CCD) camera systems employed in preclinical studies and in human investigational studies.

RESULTS

The results show that intensified CCD systems offer greater contrast with larger signal-to-noise ratios in comparison to their unintensified CCD systems operated at clinically reasonable, subsecond acquisition times.

CONCLUSIONS

Camera imaging performance could impact the success of future "first-in-humans" near-infrared fluorescence imaging agent studies.

Quality analysis of in vivo near-infrared fluorescence and conventional gamma images acquired using a dual-labeled tumor-targeting probe

The cyclic peptide, cyclopentapeptide cyclo(lys-Arg-Gly-Asp-phe) (c(KRGDf)), which is known to target alpha(v)beta3 integrin, is dual-labeled with a radiotracer, (111)indium, for gamma scintigraphy as well as with a near-infrared dye, IRDye800, for continuous-wave (cw) imaging of alpha(v)beta3 positive human M21 melanoma in xenografts. Twenty-four hours after administration of the dual-labeled peptide at a dose equivalent to 90 microCi of (111)In and 5 nmol of near-infrared (NIR) dye, whole-body gamma scintigraphy and cw imaging was conducted. Image acquisition time was 15 min for the gamma scintigraphy images and 800 ms for the optical images acquired using an NIR sensitive intensified charge-coupled device. The results show that while the target-to-background ratio (TBR) of nuclear and optical imaging were similar for surface regions of interest and consistent with the origin of gamma and NIR radiation from a common targeted peptide, the signal-to-noise ratio (SNR) was significantly higher for optical than nuclear imaging. Furthermore, an analysis of SNR versus contrast showed greater sensitivity of optical over nuclear imaging for the subcutaneous tumor targets. While tomographic reconstructions are necessary to probe TBR, SNR, and contrast for interior tissues, this work demonstrates for the first time the direct comparison of molecular optical and planar nuclear imaging for surface and subsurface cancers.

Optimization of technetium-99m Sestamibi single-photon emission tomography to define multidrug resistance with confidence

BACKGROUND

The efflux rate of technetium-99m Sestamibi (99mTc-Sestamibi) is a kinetic phenomenon related to the response of cancer cells to chemotherapy, and may be used to determine drug resistance. Measurement of the efflux rate requires accurate quantitative single-photon emission tomography (SPET) imaging within the time constraints imposed by the kinetics of the process.

METHODS

A phantom study, at activity concentrations typically found with 99mTc-Sestamibi in vivo, was undertaken to optimize the SPET parameters and, in particular, to determine whether 180 degrees acquisition arcs with heads in 'L' configuration could be used for accurate quantification. Following the development of the most appropriate SPET protocol, a small patient pilot study was undertaken.

RESULTS

Studies designed to evaluate statistical uncertainty (noise), contrast restitution and spatial resolution of the data sets, using different acquisition and reconstruction parameters, showed that 180 degrees SPET using a 64 x 64 matrix, 6 degrees angular sampling and iterative reconstruction was optimal. Finer linear and/or angular sampling afforded negligible improvement in resolution, but markedly increased the statistical uncertainty. Comparison of 360 degrees and 180 degrees acquisitions, utilizing conventional filtered backprojection and iterative reconstruction algorithms, demonstrated that the statistical uncertainty was reduced to a greater extent for 180 degrees data collection. For 360 degrees (64 x 64) data acquisition, statistical uncertainty decreased from 15% to 11% using the iterative algorithm, whilst the 180 degrees (64 x 64) data showed a reduction from 20% to 7%, and approached values obtained by planar imaging. The efflux measurements obtained in the patient pilot study were consistent with the observed chemotherapy response.

CONCLUSION

Our study shows that 180 degrees acquisition arcs are a practical option for accurate quantitative SPET kinetic imaging for potential studies of chemotherapy response in patients with lung cancer.

Lesion detectability of a gamma camera based coincidence system with FDG in patients with malignant tumors: A comparison with dedicated positron emission tomography

OBJECTIVE

The aim of this study was to investigate the lesion detectability of a gamma camera based coincidence detector system (c-PET system) in comparison to the dedicated PET system (d-PET system), and thereby clarify the feasibility of the clinical application of this system and also describe any factors influencing the lesion detectability of the c-PET system.

METHODS

We examined 74 patients including 19 with malignant lymphoma, 16 with lung cancer, 9 with primary malignant bone tumor, 7 with esophageal cancer, 6 with malignant melanoma, 3 with hepatocellular carcinoma, 3 with primary unknown cancer, 2 with breast cancer, 2 with colon cancer, and 7 with others. d-PET images were obtained using ECAT EXACT HR+ at 60 min, followed by c-PET imaging using ECAM at 120 min after the injection of 185 MBq of FDG. Each image was reconstructed without any attenuation correction. In the image interpretation, the whole body was classified into 16 regions (5 superficial regions and 11 deep regions). The FDG accumulation of the lesions was evaluated by visual grading based on the consensus of three nuclear medicine physicians, and the findings were classified into three grades; (++), (+), and (-). The lesions were also classified into 3 groups according to their size: large group (> or =2 cm), middle group (1 < or = <2 cm) and small group (<1 cm).

RESULTS

In 627 regions, the abnormal FDG uptake was detected in 109 regions by the d-PET system. Out of 109 regions, the c-PET system could detect the lesions in 91 regions and was false positive in 1 region. Therefore, the sensitivity, specificity, and accuracy of the c-PET system were 83.5%, 99.8% and 97.0%, respectively. Lesion detectability of the small group (54.5%) was significantly lower than that of the large group (97.9%) (p < 0.001) and that of the middle group (93.1%) (p < 0.001); however, the difference in lesion detectability between the large and middle groups was not significant. Neither the degree of FDG accumulation nor the location of the lesion markedly influenced the lesion detectability of the c-PET system. However, when we focused on the large and middle size lesions, the detectability of deep lesions tended to be lower than that of superficial lesions.

CONCLUSION

In conclusion, the lesion detectability of the c-PET system was inferior to that of the d-PET system, especially in the case of small lesions. Further examination is required to assess the clinical usefulness of the c-PET system.

Detection of recurrent colorectal carcinoma by 18F-FDG: comparison of the clinical performances of FDG PET and FDG CDET

OBJECTIVES

To assess the clinical performance of fluorodeoxyglucose positron emission tomography (FDG PET) using either a coincidence (CDET) gamma camera or PET equipment with Nal crystals for the detection of recurrences of colorectal cancer.

METHODS

From July 1997 to December 1999, 290 examinations were performed in 244 patients using a CDET gamma camera (2-dimensional system with 19 mm thick crystals). Additionally, from January 2000 to July 2002, 354 examinations were performed in 303 patients using PET (3-dimensional system with Nal crystals).

RESULTS

Four hundred and seventy-three of the 644 examinations performed were evaluable on the basis of histological data (202 examinations) or more than 6 months of follow-up (273 examinations). The performances of the two systems were equivalent on a patient basis (sensitivity, specificity and accuracy of dedicated PET was 92%, 84% and 90%, respectively; and sensitivity, specificity and accuracy of CDET was 90%, 94% and 91%, respectively). On a site basis, a highly significant reduction in sensitivity was observed for lesions < or = 10 mm vs. > 10 mm with both PET and the CDET gamma camera, but no difference was observed between PET and CDET according to the size of the lesions.

CONCLUSION

For detection of recurrent colorectal carcinoma, a 2-D coincidence gamma camera with 19 mm thick crystals and optimized acquisition and reconstruction parameters provides similar results in terms of accuracy, both per patient and per site, to those of an Nal PET camera.

Gamma camera coincidence imaging with [18F]fluorodeoxyglucose in the pretreatment evaluation of patients with oesophageal cancer

This study investigated the role of [18F]fluorodeoxyglucose (FDG) dual-head gamma camera coincidence imaging (GCI) in the pretreatment evaluation of patients with oesophageal cancer. Twenty-two patients (20 men; mean age, 64 years) with untreated, biopsy proven squamous cell carcinoma of the oesophagus underwent positron emission tomography (PET) and GCI 1 and 3 h after a single injection of FDG, respectively. Computed tomography (CT) was performed within 2 weeks of the FDG imaging. The sensitivity of lesion detection was compared between GCI and PET. Regional (N) and distant (M) metastases detected by GCI were evaluated with reference to PET and CT. The staging obtained by each modality was also compared with pathological staging in nine patients who underwent surgery. FDG PET detected 22 primary tumours, 34 metastatic lymph nodes and four organ metastases. Of them, GCI detected all primary tumours, 24 (71%) metastatic lymph nodes, and none of the organ metastases. Lymph nodes missed by GCI were smaller in size and the majority of them were located in the thoracic region. GCI provided N and M staging identical to CT and PET in eight patients and improved staging over CT in four patients. On the other hand, GCI missed metastases detected by both PET and CT in five patients. The addition of GCI to CT could improve detection of patients with metastasis to 82% (18/22) compared with 64% (14/22) detected by CT alone. In patients with pathological staging (n = 9), GCI could influence management changes in two patients (22%). In conclusion, FDG GCI has a role that is complementary to CT in the initial staging of patients with oesophageal cancer, and due to the additional detection of nodal metastasis, GCI can provide staging information, which may influence changes in management.

Positron emission tomography imaging in nonmalignant thoracic disorders

The role of the fluorodeoxyglucose (FDG) technique positron emission tomography (PET) is well established in the management of patients with lung cancer. Increasingly, it is becoming evident that FDG-PET can be effectively employed to diagnose a variety of benign pulmonary disorders. Knowledge of such applications further expands the domain of this powerful modality and further improves the ability to differentiate benign from malignant diseases of the chest. We describe pertinent technical factors that substantially contribute to optimal imaging of the thoracic structures. Particularly, the complementary role of attenuation correction (AC) to that of non-AC images is emphasized. We further outline the need for and the state of the art for co-registration of PET and anatomic images for diagnostic and therapeutic purposes. We then review patterns of physiologic uptake of FDG in thoracic structures, including the lung, the heart, the aorta and large arteries, esophagus, thymus, trachea, thoracic muscles, bone marrow, and joints and alterations following radiation therapy to the thorax. A great deal of information is provided with regard to differentiating benign from malignant nodules and in particular, we emphasize the role of dual time point imaging and partial volume correction for accurate assessment of such lesions. Following a brief review of the diagnostic issues related to the assessment of mediastinal adenopathies, the role of FDG-PET imaging in environment-induced lung diseases, including pneumoconiosis, smoking, and asthma are described. A large body of information is provided about the role of this technology in the management of patients with suspected infection and inflammation of the lungs such as acquired immunodeficiency syndrome, fever of unknown origin, sarcoidosis, chronic granulomatous disease and monitoring the disease process and response to therapy. Finally, the value of FDG-PET in differentiating benign from malignant diseases of the pleura including asbestosis-related disorders is described at the conclusion of this comprehensive review.

PET imaging using a triple-head gamma camera

Interest in clinical fluorodeoxyglucose (FDG) imaging with multiple-head gamma cameras is growing. To improve sensitivity, triple-head coincidence imaging has been proposed. We report our initial experiences with a triple-head coincidence gamma camera with 19 mm sodium iodide crystal thickness. Several positron emission tomography-image quality parameters were evaluated using a Carlson and line source phantom. The system sensitivity with two-dimensional axial shields was 830 cps kBq-1 ml-1 and maximum noise equivalent count rate 1900 cps for an 18F-activity of 50 MBq. The imaging resolution was in central axial 7.0 mm and in central transaxial 7.6 mm, respectively. The average scatter fraction in scattered media was 29%. Clinical brain, heart and whole body images studies with [18F]FDG were acquired and they show good correlation with the phantom image quality. As a conclusion, triple-head coincidence gamma camera provides relatively high-count rate imaging with good contrast and resolution.