Greater cancer detection is possible with 4-D PET image reconstruction

ScienceDaily (June 8, 2011) — A study introduced at SNM's 58th Annual Meeting is advancing a positron emission tomography (PET) imaging method that uses new 4D image reconstruction to achieve the highest diagnostic capability for the detection of cancer. Mounting evidence shows that PET imaging, which provides visual representations of bodily functions, is significantly more sensitive when used with cutting-edge 4D image reconstruction technology that accounts for patient respiration and produces clearer, more easily interpreted images.

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"PET imaging with 4D image reconstruction could potentially help with early cancer detection, which is an imperative in the field of nuclear oncology," says Si Chen, lead author of the study, Johns Hopkins School of Medicine, Baltimore, Md. "The results of this study and our other studies indicate that the sensitivity of small cancer lesion detection for patients will likely benefit from this novel image reconstruction method, which incorporates an accurate and patient-specific respiratory motion estimation algorithm we previously developed. The improved diagnostic accuracy would allow physicians a more informed understanding of a patient's situation in order to provide better treatment planning for the best possible outcome."

The objective of the study was to quantify the improvement of PET image quality using the 4D PET image reconstruction method with respiratory motion compensation compared to a more conventional 3D PET image reconstruction method. The researchers evaluated the image reconstruction methods using the receiver operating characteristic (ROC) methodology, which is based on signal detection theory widely adopted in diagnostic radiology. A ROC curve is a graphical plot of the sensitivity versus specificity for lesion detection based on the reconstructed PET images. Realistically simulated PET images were employed in this evaluation study using the 4D XCAT phantom -- a digital anthropomorphic phantom that realistically models a typical patient's anatomy, respiratory and cardiac motions. A total of twelve spherical tumors of 10mm diameter were planted inside the lungs and liver of the phantom, which was input to realistic simulation of PET data acquisition using another methodology called Monte-Carlo simulation. The simulated PET data were then reconstructed using both imaging reconstruction methods. The researchers used a mathematical observer, i.e., channelized hotelling observer (CHO), to mimic the interpretation of these PET images by human observers.

Using these methodologies, researchers were able to compare the sensitivity and specificity of the two image reconstruction methods and found that the 4D PET image reconstruction method with respiratory compensation improved the detection sensitivity for the cancer lesions in the liver and lungs. This indicates that evaluation of cancer for lesions smaller than 10 millimeters could be enhanced by compensating for respiratory motion with the 4D image reconstruction method.

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Hybrid PET and MRI imaging on the horizon: Shows promise for the detection of cancerous tumors

ScienceDaily (June 6, 2011) — Preliminary research presented at SNM's 58th Annual Meeting is breaking new ground for the development of a brand new hybrid molecular imaging system. Simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) is providing important diagnostic information about soft tissues and physiological functions throughout the body. Scans focused on screening suspicious lesions for cancer are already comparable to more conventional molecular imaging methods. Further research could lead to the clinical use of PET/MRI as an additional tool for detecting cancer and other diseases.

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"Combining MRI technology with PET in a single integrated system adds the advantages of the extremely broad spectrum of diagnostic MRI procedures to the arsenal of available PET procedures," said Alexander Drzezga, MD, TU Muenchen, Munich, Germany, lead author of the study. "This could potentially result in the development of new imaging agents that bring together specific diagnostic strengths of PET and MRI. It offers exciting scientific options to image physiologic and pathophysiologic processes at the same time and to improve our understanding of both. This and further studies could potentially open a whole new hybrid imaging discipline within the field of nuclear medicine."

The most commonly used hybrid molecular imaging technology is the PET/CT system. MRI shows some advantages for combination with PET when compared to computed tomography (CT), which uses X-ray technology to capture structural information but it is not as sensitive as MRI data in terms of soft tissue contrast. CT images of certain areas of the body -- including the brain, head and neck, and pelvis -- provide restricted resolution of anatomical structures. MRI technology is excellent for imaging these complex areas of soft tissue and may provide answers to unresolved musculoskeletal questions. In combination with PET, MRI may also have value for imaging liver and breast tissues and would provide a useful tool for imaging children due to its reduced radiation dose.

Simultaneous PET and MRI imaging has been a tricky business, as the magnetic field of MRI technology has limited PET imaging in the past, specifically the photomultipliers needed for data acquisition. Previous prototypes have been simply side-by-side designs or were solely for imaging the brain. The advent of "avalanche photodiodes" and their introduction to the new, fully integrated and whole-body PET/MRI prototype used in the current study is a leap forward for this technology. A number of these integrated scanners are available for research purposes worldwide. It is speculated that these systems will grow rapidly in number if clear clinical benefit continues to be demonstrated.

For this study, eleven patients with cancer diagnoses underwent dual-imaging single-injection PET/CT imaging followed by PET/MRI imaging. Simultaneous PET/MRI acquisition was feasible and offered good-quality PET and MRI diagnostic data. Tracer-uptake was similar in relation to lung, liver, spleen and bone scanning, all acquired within a short examination timeframe. Results already indicate that combined PET/MRI shows comparable performance in the detection, diagnosis and allocation of suspected tumors in patients with oncological diagnoses as compared to conventional PET/CT.

The next step for PET/MRI is studying the added benefit of introducing sophisticated MRI sequences to the diagnostic imaging protocol. This and other related studies may lead to the establishment of hybrid PET/MRI imaging as a new diagnostic imaging system similar to PET/CT for its effectiveness and ability to provide a wealth of both functional and anatomical information about the body.

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Gamma imaging provides superior tumor detection for dense breasts

ScienceDaily (June 6, 2011) — A study revealed at SNM's 58th Annual Meeting is comparing the breast-tumor detection capabilities of two very different imaging technologies -- breast-specific gamma imaging (BSGI), which provides functional images of breast physiology, and ultrasound -- for women with complex breast imaging cases that require further evaluation. Many women who have dense breast tissue (radiodense breasts) are difficult to image using mammography, currently the gold standard of breast imaging. For women whose mammograms are not clear enough to determine whether cancer is present, support methods such as BSGI and ultrasound are used to answer any remaining diagnostic questions.

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"A lot of white shows up on the mammograms of women with radiodense breasts, and it becomes a lot like trying to find one cloud in a cloudy sky," says Douglas Kieper, BSNMT, professor and nuclear medicine research supervisor at Hampton University, Hampton, Va. "This study tells us that BSGI improves our ability to detect breast cancer when combined with other breast imaging techniques. What we are really looking at is the impact that BSGI and ultrasound have on breast cancer patient management. Comprehensive breast imaging including BSGI could improve breast cancer detection and provide a better prognosis for breast cancer patients."

According to the American Cancer Society, breast cancer is the foremost form of cancer developed by women, except for skin cancer. An estimated 207,090 women were diagnosed with breast cancer and approximately 39,840 died of the disease in 2010. Current statistics estimate that a woman's chance of developing the disease is slightly less than one in eight women. Mammography catches about 85 percent of breast cancers in women with normal breast tissue but only 60 percent in women with dense breast tissue. Instead of relaying information about the structure or anatomy as mammography and ultrasound imaging do, BSGI informs clinicians about functions of the breast tissues, specifically changes in tumor tissues that could be essential to appropriate treatment planning, whether for biopsy, lumpectomy or cancer therapy.

BSGI, also known as molecular breast imaging, is most valuable for women who have an unresolved diagnostic concerns after mammography. These are often labeled as BIRADS 0 mammograms according to the Breast Imaging Reporting and Data System. Breast cancer patients receive a score that assesses cancer in the range of one to six, the latter being confirmed malignancy. BIRADS 0 means that there is insufficient information and further evaluation is necessary, whether the patient has dense breasts, had negative results during a mammogram but nipple discharge, or has a family history of breast cancer.

For this study, 119 patients from four medical centers scheduled for BSGI evaluation were added to a registry, and results of their routine exams were collected for analysis. Results of both routine BSGI and ultrasound imaging were collected and compared for their ability to provide additional information about the case and change breast cancer patient management. Of the 119 subjects, 102 lesions were benign, 25 were malignant and 2 were labeled as high-risk for cancer. BSGI changed the diagnosis for 109 participants compared to ultrasound, which changed patient management in 71 cases. BSGI offered greater sensitivity for detecting breast cancer (100 percent versus 77 percent with ultrasound) and greater specificity, being negative in benign cases (82 percent versus 52 percent of cases with ultrasound).

Molecular breast imaging is continually expanding. If future studies also prove that BSGI imaging is clinically useful for patient management and the cost of technology and radiation dose are reduced with technological advancements, BSGI could potentially become an accepted imaging technique for initial cancer screening. Until then, BSGI is an effective tool for providing clinicians with additional information about complex breast cancer cases and could potentially improve cancer outcomes for women.

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Important step towards early detection of breast cancer

ScienceDaily (May 18, 2011) — European researchers have developed a clinical PET system with the highest resolution and sensitivity in the market, specifically dedicated to breast cancer detection in early stages. The MAMMI (MAMmography with Molecular Imaging) device will allow doctors to start treatments one or even two years earlier than usual and also evaluate the patient's response to chemotherapy.

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Coordinated by José María Benlloch, researcher of the Spanish National Research Council (CSIC) and co-director of the Institute for Molecular Imaging Instrumentation (I3M), the MAMMI Project was created by a multidisciplinary team of eight European research institutions and companies, ranging from medical oncology and pharmacokinetics research to molecular imaging instrumentation, advanced image processing software and integrated electronics circuit design.

The device is currently installed in the National Cancer Institute in Amsterdam (Netherlands) and was previously set up at the clinic of the Technical University of Munich (Germany), where they have completed the clinical research and examined over fifty patients. The new system will shortly be installed in the Provincial Hospital of Castellón (Spain) and other international hospitals have shown their interest in purchasing it.

The most striking novelty of the mammogram is the way it captures the image. The patient lies face down on a special table, and enters a breast in one of the openings. Beside the stretcher, the specialist positions a trolley that incorporates the detection system based on a gamma ray sensor.

The picture is taken without compressing the breast thanks to the ring shape of the detector that surrounds the pendant breast. According to Dr Benlloch: "This significantly improves the visualisation and diagnosis because sometimes there are tumours that are very close to the base of the pectoral muscle."

This new mammogram also provides greater patient comfort. In this sense, the Biomechanics Institute of Valencia (IBV) assessed the company ONCOVISION in the design, manufacturing, and mechanical tests of the stretcher, and applied user-friendly design methodologies and ergonomic criteria. For example, lifting columns were added to the table to facilitate its use by the elderly and disabled.

The PET system

The other major innovation is the technique used. The traditional mammogram is an x-ray of mammary glands. MAMMI, however, is based on the PET technique (Positron Emission Tomography) for the diagnosis of breast cancer, which offers numerous advantages.

In the first stages of a cancer, the malignant cells replicate in an uncontrolled way and, after one to two years, cause a lesion that is visible with the current techniques. After that, the lesion extends and takes about another year until it can be felt.

While current diagnostic equipment is based on morphological images and does not recognize the cancer until there is a lesion, the MAMMI PET measures the metabolic activity of the tumour by locating the high glucose uptake of the cancer cells. This allows the specialist to detect the disease much earlier and numerous studies have confirmed that early detection reduces mortality by 29%.

Until now, whole-body PET scans were indicated for breast cancer patients or for people with a high risk of suffering the disease. However, the result is a low resolution image and therefore does not detect small tumours. "Our device, however, is devoted exclusively to breasts so the detectors are very close to this part of the body and show tumours in early stages," explains Luis Caballero, head of the project in ONCOVISION.

In comparison, MAMMI can see lesions as little as 1.5 mm, while the best of the systems that currently exist offers a resolution of 5 mm. The system generally improves the diagnosis of all patients, but it is especially effective for women with breast implants or young women whose breast density has always made obtaining a clear image difficult.

Assessment in later stages

The mammography device marketed by the Valencian company can also monitor whether the treatment the patient with breast cancer is following actually works. According to Dr Caballero: "By showing the uptake of glucose, the PET technique is the only one able to reveal whether there are still cancer tissues after an operation, since with the other techniques it is impossible to distinguish tumour tissue from the scar left by the operation."

Also, the PET reveals whether the therapies of radiation and chemotherapy are effective or need to be modified. As MAMMI is a more precise PET instrument, it ensures a better assessment of tumour activity and its response to therapy.

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