Current Medical Imaging - Volume 5, Issue 3, 2009

Full text available

The ultimate goal of animal studies using advanced imaging technology is to understand and conquer human ailments. Studies of small and large animals provides approximation to human to different degrees. The first part will review the general requirements of small animal imaging. It will be illustrated by our experience in small animal imaging (microPET, scintigrams, CT and MRI) using rats to examine locoregional radionuclide cancer therapy. The technical requirements and requisites for translation to human studies will be discussed. The second part will examine requirements in large animal imaging, illustrated by our dog studies involving PET, PET/CT, MRI and dosimetry to provide closer approximation to human dimensions and for the design of clinical trials. The main objective is to familiarize the theoretical bases and practical requirements to carry out animal imaging studies for meaningful translation research.

Remarkable prospect has been demonstrated because of the efficacy of cellular transplant therapies based on neural stem/progenitor cells (NS/PCs) for some central nervous system (CNS) diseases. To develop this promising therapy, some important issues need to be resolved. The critical link is to develop a noninvasive technique that is able to monitor physiological state, namely the metabolic variations of the NS/PCs after operation. The magnetic resonance spectroscopy (MRS) will be capable of meeting this requirement, rather than other relevant techniques, such as magnetic resonance imaging (MRI), position emission tomography (PET). After understanding the features about metabolic profiles of NS/PCs, it will be available to trace them in alive organism. To date, some studies about metabolic characteristics of the NS/PCs have been reported. The Myo-inositol and Phosphocholine are both enriched in NS/PCs spectrum, and the 1.28 parts per million (ppm) biomarker is probably their specific resonance. These discoveries caused a tremendous commotion in the scientific field, however, some concerns with doubt were also reported. Therefore, more evidences and studies will be needed. Acquiring the metabolic profiles of NS/PCs has great significance, not only for assessing the efficacy of cellular transplant therapies, may be, but also for understanding the origin of the brain tumors.

Image fusion between different “anatomic” imaging modalities such as CT or MRI with the “functional” radionuclide images (positron emission tomography, PET, or single photon emission tomography, SPECT) has been shown to give very useful clinical information. This image fusion technique is now implemented in several, commercially available PET-CT and SPECT-CT, and very recently also PET-MRI scanners. Involvement of ultrasound (US) in image fusion has obvious potential benefits compared with the other imaging modalities: real-time images, possible bedside examinations and ease of image-guided biopsies. However, two important challenges comprise the lack of a DICOM standard in US and the fact that being a real-time examination, it either means fusion of previously recorded static US images or live fusion, which has been applied to liver, prostate, brain and vessels. A review is presented of the current literature involving US in image fusion from peer-reviewed journals in English, to give an overview of the current and future possibilities with this technique.

In high intensity focused ultrasound (HIFU) experiments it is found that the center of the heated region is always deviated from the geometrical focus point of transducers. This phenomenon is called the shift of the focus region (SFR). To achieve optimal result in HIFU treatment, the focused region should be adjusted to compensate the shift. In this paper, a quantitative method to measure SFR is proposed and applied to the experiments for porcine tissues in vitro by the authors. In the experiments it is observed that the maximum SFR which are towards to the HIFU transducer can exceed 1 cm.

Recent technical advances and a renewed interest in protection of patients against the danger of ionizing radiation have prompted new trends in interventional radiology. Therefore this paper presents a review on the state of the art in the field of both radiation doses and image quality optimization in interventional radiological procedures. After a summary of recent progresses in this area, an overview of physical parameters suitable for measuring the doses to patients in interventional radiology is introduced: indeed in these procedures both stochastic and deterministic risks have to be assessed, and then many “dose indicators” can be used (fluoroscopy time, dose-area-product, cumulative dose at the interventional reference point, etc.). Some National Authorities are transferring the principle of using reference levels of doses from plain film radiology to interventional examinations in order to optimize the procedures, and careful considerations have to be done about the very large variations in doses among different centres. Together with the dose issues, one must also consider the quality of the generated image: the three main image-quality physical parameters (i.e., contrast, sharpness, and noise) are interdependent, and therefore in interventional radiology the goal is to reduce the patient dose to the minimum level that will generate an image with an acceptable degree of noise, that is, to produce an “adequate” image, even if it is not a “perfect” image. Finally, a review of features available to optimize the full interventional procedure (image receptor, last image hold, pulsed fluoroscopy, spectral filtration, collimation, and virtual collimator) is given.

Acupuncture, an ancient therapeutic technique, is currently gaining popularity as an important modality of alternative and complementary medicine in the West world. Concurrently, scientific interests in exploring whether acupuncture is therapeutically effective are raised alongside those about the means by which it may operate. Modern neuroimaging techniques such as functional magnetic resonance imaging, positron emission tomography, electroencephalography, and magnetoencephalography provide a means to safely monitor brain activity in humans. In this review, we have summarized evidence derived from the neuroimaging studies and tried to elucidate the neurophysiological correlates of acupuncture. Previous investigations on the neural responses to acupuncture mainly focus on its acute effects and explore the correlation between the specific acupoints and cortical activations only in the spatial domain. However, abundant clinical reports and psychophysical analysis suggest the kinetics of acupuncture is longer acting as a function of time. Consequentially, an accurate interpretation of acupuncture actions depends on how effectively we can characterize the nature of temporal variations underlying neural activities, rather than simply detect the occurrence of such changes. This emerging picture indicates that both designing paradigms and statistical models involved in acupuncture studies should be applied with great care.

ventilation/perfusion scintigraphy (V/PSCAN) was the procedure of choice for studying patients with suspected pulmonary embolism (PE) until the prospective evaluation of V/P imaging in the study known as PIOPED I revealed high number of non diagnostic findings. This has challenged development of computed tomography (CT) during 1990s. Since beginning of 2000, multidetector CT (MDCT) is widely applied and has become the most commonly used technique in patients with suspected PE. The current MDCT have very advanced technology and have improved ability to detect small emboli. Unfortunately, results of the most advanced MDCT are still compared with V/PSCAN results performed in PIOPED I 20 years ago. However V/PSCAN has further developed. Tomographic technique V/PSPECT is taking over V/PPLANAR. Probabilistic criteria are replaced by holistic criteria for interpretation, taking lessons learned from PIOPED I. Discussion is focused on diagnostic value for MDCT and V/PSPECT. MDCT and V/PSPECT are both indispensible imaging techniques to study patients with suspected PE. However, when available, V/PSPECT should be the preferred method for diagnosis of PE, primarily due to the lower radiation exposure and applicability to all patients. Therefore it is our duty to make V/PSPECT generally more available, to use holistic interpretation knowledge and to communicate daily with the clinicians, so that the best technique is used in all patients. In conclusion MDCT cannot replace V/PSPECT. MDCT and V/PSPECT are complementary rather the competitive!

The purposes of this article are to review the computed tomography (CT) and magnetic resonance imaging (MRI) findings of various solid pancreatic masses and to correlate them to pathologic features, to illustrate typical and atypical imaging findings of solid pancreatic masses, and to learn the crucial CT and MRI findings in differentiating solid pancreatic masses. Presenting cases are divided into three categories as solid tumors, cystic tumors mimicking solid masses, and tumor-like lesions. Review of CT and MRI findings is performed and imaging-pathologic correlation is performed. Typical and atypical cases are presented. The major teaching points of this article are as follows; atypical presentations of solid pancreatic masses may give us much instructive information, detailed evaluation of the morphological features as well as enhancement pattern on dynamic study is essential in diagnosing solid pancreatic masses, and signal intensity of the lesion on MRI can play an important role in differentiating solid pancreatic masses.

Aim: To review the imaging features of alveolar echinococcosis in eight patients with involvement of different organs. Material and Methods: Ultrasound (US) and computed tomography (CT) examinations were performed in all patients, and magnetic resonance imaging (MRI) and color Doppler ultrasound (CDUS) were performed for two patients. Three patients had involvement of only the liver; two had involvement of lung and liver; one had involvement of only the lung; one had involvement of liver and sternum; and one had lung, liver, and adrenal involvement. The diagnosis was confirmed by histopathologic examination in all patients. Results: The lesions located in the liver were generally seen as heterogeneous hypoechogenic on US, hypodense on CT, and hypointense solid masses on MRI. These masses included necrosis and calcifications. Vascular flow on CDUS and contrast enhancement on CT and MRI were not observed in any of the lesions. On CT, lung lesions were seen as multiple, nodular, well-defined or ill-defined opacities; some had cavitations caused by necrosis. Conclusion: Knowledge of imaging characteristics of alveolar echinococcosis makes it possible to provide an early diagnosis radiologically. In addition, radiologic findings have an important role in the follow-up. Ultrasound, CT, and MRI are complementary methods in the diagnosis of alveolar echinococcosis.