Current Medical Imaging - Volume 3, Issue 1, 2007

Cancer remains one of the major causes of death in the Western world, and it is increasing in developing countries as well as in the industrial world. The overall costs of cancer management relentlessly increase year on year. Therefore, there are huge challenges ahead for all those involved in the care of cancer patients that include the development of new and more effective therapies and the development of new technologies to diagnose cancer at an earlier stage, to define the presence and extent of established tumors more accurately, and to monitor new therapies directed at specific biological targets. Imaging is now recognized as pivotal to the management of cancer patients, and oncologic imaging is an increasingly large component of the general workload in the radiologic department. The multichannel computed tomography (CT) is transforming axial CT into a 3D modality, and the positron emission tomography (PET) integrated with CT provides a precise tumor localization combined with exquisite anatomical and morphological details. The important development in ultrasonography is an introduction of non-destructive microbubble contrast agents for enhancing vascular structures or lesions. In this issue there are seven excellent updated review articles including three dealing with evaluation of various cancers utilizing different imaging modalities (restaging renal cell cancer with F-18 FDG PET, diagnosing prostate cancer in Spain using color doppler ultrasonography and detection of hepatic metastases with contrasted ultrasonography), one summarizing use of micro-CT in basic animal research, one reporting safe and effective laser thermal ablation (LTA) therapy of small hepatocellular carcinoma, and one demonstarting variants and artefacts of bone mineral density (BMT) study using dual-energy X-ray absorptiometry (DEXA) which is widely used in clinical practice for the management of osteoporosis. The demand for BMD and physician visits related to osteoporosis has seen a dramatic increase with a significant publicity. The precision of DEXA analysis is what makes the technology such a clinically useful tool. The interpreter should be vigilant with regard to the proper bone margins and the presence of mettallic hardware or artefacts.

The rapidly growing field of PET imaging is providing new opportunities to define target volumes for radiotherapy. For multiple disease sites, PET has become a tool to provide a way to locate the most rapidly metabolizing portions of the lesion mass and to detect unsuspected metastases over conventional CT imaging. This made PET a desirable imaging modality for radiotherapy treatment planning. In addition to improved staging and target definition, radiotherapy has benefitted from the use of PET as a therapy response tool. Introduction of combined PET/CT units has accelerated the proliferation of PET into treatment planning. Today there are many radiation therapy departments either has a PET scanner of their own or access to PET images. We are, now, in the era of solving problems of PET imaging for smooth integration into radiotherapy. However, in the future we will be beyond hyper-metabolic tissue characterization and incorporation of this information into functional treatment planning. New lesion markers under development in animal models today will inevitably be translated into clinical studies. With advances in computer and biotechnology, in the near future, it may be possible to give a cocktail of tracers to patients so as to generate multi-dimensional information, to further improve the radiobiological characterization of the target volume for consideration in the radiation treatment planning. This review provides an introduction to the subject of the use of PET for radiotherapy for clinicians. It also outlines today's and tomorrows challenges for successful integration of PET imaging into radiotherapy.

The incidence of Renal Cell Carcinoma (RCC) is increasing at all stages. Thus, there is a need to develop more accurate and reliable methods of diagnosing, staging and treating the disease. The role of positron emission tomography (PET) is still evolving with regard to the diagnosis, staging and management of RCC. At present, the assessment of renal masses and primary staging of RCC are reasonably well investigated using computed tomography and ultrasound. However, many masses are still excised that are benign or understaged. PET with 18F-Fluorodeoxyglucose (FDG) has been useful with re-staging RCC and in certain cases where conventional studies, including bone scan, are inconclusive. The value of PET radiotracers in RCC other than FDG, the standard one used in oncology, is under investigation. We review the current status of PET in RCC and examine the recent development of PET/CT with its impact on renal mass imaging due to its ability to contemporaneously acquire and co-register data, to localize elevated FDG uptake with improved anatomic specificity. New radiotracers, such as those created by radiolabelling of antibodies (e.g. labelled G250, a protein overexpressed in RCC cells) and how they may impact on the diagnosis and future treatment of RCC are also outlined.

Objective: The last decade has seen numerous modifications in the way the prostate cancer is diagnosed. Current diagnostic methods in prostate cancer lacking the ability to predict individual patient outcome, which highlights the need for more sensitive approaches. We investigated the value of digital rectal examination (DRE), transrectal ultrasonography (TRUS) and prostatic specific antigen (PSA) analysis as aids in general clinical practice and in the early detection of prostate cancer. The purpose of this paper is to evaluate the efficiency and effectiveness of analytical and imaging methods for diagnosing prostate cancer in the north-west Spain. Material and Methods: We investigated prospectively two groups of patients (in all 760) with pathological DRE or PSA. Sensitivity (Se), specificity (Sp), Positive predictive Value (PPV), Negative Predictive Value (NPV), Receiver Operating Characteristics (ROC) curves and other analyses were performed to determine the relative contributions of PSA, DRE, TRUS, Colour Doppler Ultrasound (CDUS), symptoms and patient age to cancer prediction. Results: The presence of prostatic disease symptoms did not distinguish between subjects with and without cancer (p=0.8450). The most sensitive (98%) was total PSA (>4 ng/ml) and the most specific were DRE (78%) and TRUS (65%). The contribution of PSA, DRE and TRUS to the diagnosis of prostate cancer was significant (p<0.05). In patients with a PSA of 4-10 ng/ml, using a threshold PSA specificity increased, using a free/total PSA ratio of 15%. Both echographic methods were effective (p<0.05), with greater specificity for CDUS. Conclusion: The PSA continues to be the most sensitive method for prostate cancer diagnosis. DRE tends to be more negative at early stages of cancer detection. Comparing the conventional TRUS echography with the CDUS, the latter is a better detector in the diagnosis of cancer.

Detection of liver metastases is one of the most common problems in evaluating patients with primary neoplasms. Gray-scale and color Doppler ultrasonography have limited accuracy with a sensitivity ranging between 53% and 77%. Isoechoic metastases and nodules under 1 cm in size may not be detectable. Occasionally, non-metastatic liver lesions can be identified in neoplastic patients which must be correctly characterized. Microbubble contrast agents overcome many limitations of gray-scale ultrasonography to detect liver metastases and increase the possibility to differentiate them from other focal liver lesions. In this review article we discuss the current role of contrast enhanced ultrasonography in detection of liver metastases using specialized destructive and non-destructive modes. Using air-filled microbubbles and destructive modes the sensitivity of contrast enhanced ultrasonography to detect liver metastases ranges between 80% and 98%. The ease of use of the non-destructive approach makes it much more attractive and is particularly helpful for lesion characterization. An increasing number of studies is being published regarding the diagnostic performance of perfluorocarbon- or sulfur hexafluoride-filled microbubbles with non-destructive modes to detect liver metastases, and the general agreement is that sensitivity and specificity of the non-destructive modes approach those of the destructive approach and of helical CT.

Micro Computed Tomography (micro-CT) was suggested in biomedical research to investigate tissues and small animals. Its use to characterize bone structures, vessels (e.g. tumor vascularization), tumors and soft tissues such as lung parenchyma has been shown. When co-registered, micro-CT can add structural information to other small animal imaging modalities. However, due to fundamental CT principles, high-resolution imaging with micro-CT demands for high x-ray doses and long scan times to generate a sufficiently high signal-to-noise ratio. Long scan times in turn make the use of extravascular contrast agents difficult. Recently introduced flat-panel based mini-CT systems offer a valuable tradeoff between resolution (∼200 μm), scan time (0.5 s), applied x-ray dose and scan field-of-view. This allows for angiography scans and follow-up examinations using iodinated contrast agents having a similar performance compared to patient scans. Furthermore, dynamic examinations such as perfusion studies as well as retrospective motion gating are currently implemented using flat-panel CT. This review summarizes applications of experimental CT in basic research and provides an overview of current hardware developments making CT a powerful tool to study tissue morphology and function in small laboratory animals such as rodents.

Measurement of bone mineral density (BMD) with dual-energy X-ray absorptiometry (DXA) is widely used in clinical practice for the diagnosis of osteoporosis and assessment of fracture risk. However, variants and artefacts such as, osteophytes and metallic objects can affect the BMD results of the spine and hip. We demonstrate a spectrum of clinical examples that may impact on BMD evaluation. Recognition of such artefacts is important for the correct interpretation of these studies.