Current Medical Imaging - Volume 11, Issue 3, 2015

The purpose of this research is to provide an unsupervised precise measurement technique in tracking the change of brain parenchyma volume over time. Tracking this change can be a very useful imaging metric for neurological patients who may develop brain dementia overtime. This technique should help in assessing the patient diagnosis, progress, and response to medication. A novel unsupervised segmentation technique was developed to measure the brain parenchyma volume with a high degree of precision. The technique consisted of two stages. The first stage used a novel manner of multi-spectral analysis and the second stage used a series of morphological filters coupled with several logical image operators to remove possible segmentation outliers. This technique required dual spin echo T2 weighted MR data of the brain. Twenty MR data sets were segmented and the accuracy was evaluated visually and found to be free of outliers. The precision of the technique was tested on a series of MR data sets for two normal subjects. Each series consisted of seven MR data sets per subject scanned over a month period. The percent brain parenchyma was calculated for the two subjects with a percent coefficient of variation of less than 0.4%. The technique ran on a standard personal computer in less than 30 seconds per data set without user interaction. This research provided an unsupervised, precise, and fast technique to track the progression of change in brain parenchyma volume.

Despite the high sensitivity of magnetic resonance imaging (MRI) in detecting a wide spectrum of various pathological processes, the specificity of the method to differentiate among these pathologies and its ability to predict clinical outcomes has been rather below initial expectations. The main problem arises from the fact that most of the pathologies of the spinal cord manifest with a rather nonspecific increase of water protons, reflecting local oedema or gliosis. This is a common finding in most myelopathies, which does not allow a further differential diagnostic distinction in most cases. The use of contrast media improved the specificity of the method; however, it is still challenging to differentiate types of myelopathies. Advanced imaging methodologies such as functional MRI (fMRI), diffusion-weighted and -tensor imaging (DWI/DTI), Magnetic Resonance Spectroscopy (MRS) have been used in the evaluation of neurologic diseases in the brain and have gained increased acceptance among the clinicians for improving the specificity of MR technology and for their ability to better correlate with functional disabilities and clinical symptoms thus providing predictive information about potential outcome. Preliminary results show that, quantitative parameters extracted by these techniques from the spinal cord can provide surrogate markers of disability for determining prognosis as well. In this review, we focus on implementing advanced neuroimaging methodologies (DWI/DTI, fMRI and MRS) in imaging of the human spinal cord for better clinical assessment. Additionally, we review the recent imaging literature advances in this topics and their clinical applications.

Myocardial perfusion imaging (MPI) is routinely used for clinical evaluation and therapeutic guidance of myocardial ischemia (MI). So far, technetium-99m (99mTc) labeled Single Photon Emission Tomography (SPECT) imaging agents have been the mainstay of MPI, primarily due to the in-house availability of 99mTc radioisotope via generators and the ease of radiolabelling. Over the last decade, Positron Emission Tomography (PET) has emerged as a superior imaging technique with improved imaging quality and image quantification. To utilize the key features of PET in the diagnosis of MI, various Gallium-68 (68Ga) based PET imaging agents were designed and evaluated. Gallium-68 is a generatorbased positron-emitting nuclide and, like 99mTc, can be obtained on an as-needed basis from an in-house 68Ge/68Ga generator system. The ease of radiolabeling and optimal physical half-life of 68Ga (68 min) position it as an ideal PET isotope for MPI. The design of 68Ga-based MPI agents discussed in this review closely followed the physicochemical requirements established for clinically used 99mTc-based MPI agents. We compare and contrast various 68Ga-based complexes used in MPI animal studies and can conclude that select compounds meet the standards set by 99mTc-based MPI agents based on their physicochemical and in vivo properties.

Hepatocellular carcinoma (HCC) comprises a major subtype of primary liver cancer that could be diagnosed earlier using computed tomography (CT) examination. Video compression reduces the size of multi-frame data and induces blocking effect. This study aims to examine if the blocking effect alters the performances of HCC tumor detection and hepatic lesion classification in CT images. H.264 is considered in this study because it can compress 14-bit grayscale multi-frame data that is compatible with the image requirement of CT. A range of quantization parameters (QP) was determined in a phantom study. With this QP range, the trained support vector machines (SVM) based on image features were applied to test 20 HCC cases and 21 normal cases. The SVM performed significantly better than the random classification for detecting HCC in images compressed with the QP levels of interest. Images compressed with QP1 yielded the best performance. The same range of QP levels was applied to 15 lesion-bearing images. The image quality indices of these images were calculated to form the feature vectors. The clustering of these feature vectors identified at least six clusters. The association of the lesion classes with the identified clusters was found significant for all QP levels of interest. QP5 and QP9 yielded higher association than QP-3 and QP1. The findings proved a novel application of H.264 compression for enhancing the hepatic lesion detection classification in CT images.

MDCT is considered as the principle imaging modality utilized for evolution of suspected pancreatic cancer. But there is a subset of pancreatic cancer may be notable. Spectral CT can create monochromatic images which reduce beam-hardening artifacts, improve image quality and optimize lesion contrast. Methods: Thirty-one patients with pancreatic cancer underwent spectral CT to generate conventional 140kVp polychromatic images (group A) and monochromatic images, with energy level from 40 to 140 keV (group B) during arterial phase and portal venous phase. ANOVA compared the tumor-to-pancreas contrast-to-noise ratio (CNR), image noise, artery-totumor CNR. Readers’ subjective evaluations of image quality were recorded. Results: The lower image noise for group B was at 65-80keV during 40-80keV (p<0.05). Higher tumor-to pancreas CNR values of arterial phase and portal venous phase in group A and B were distributed at 55-65 keV (p<0.05). Artery-totumor CNR value was higher at 40-70 keV in group A and B (p<0.05). Higher image quality score were obtained at 55-65 keV than in group A and B (p<0.05). Compared with polychromatic images, tumor-to pancreas CNR values of arterial phase and portal venous phase, artery-to-tumor CNR of monochromatic images increased by 84.6%, 89.4% and 61.1%. Conclusions: The monochromatic imaging can improve image quality of pancreatic cancer and surrounding vessels by using single source dual-energy CT, and optimal energy level for display lesion, surrounding vessels were 40-65 keV and 40-70keV, respectively.

Rationale and Objectives: Despite the recent development of coronary computed tomography angiography (CCTA) allowing for significant radiation dose reductions, the impact of lower tube voltages compared to traditional voltages is still unclear. We investigate the role of decreasing tube voltage and its effect on the total dose reduction and image quality. Materials and Methods: We investigated 184 consecutive patients (age: 61±13 years; 47% male) referred for CCTA. Signal and noise [Hounsfield Units (HU)] were measured in the ascending aorta at the level of the left main origin. The contrast was calculated by [signal - HU measured in subcutaneous tissue in front of the sternum]. The signal-to-noise ratio (SNR) was calculated by [signal / noise] and the contrast-to-noise ratio (CNR) was calculated by [contrast / noise]. Signal, noise, contrast, the dose length product (DLP) and radiation dose (millisievert: mSv) were assessed between the kilovoltage (kVp) protocols. Images were scored qualitatively by two experienced readers. Results: Body mass index was significantly higher in the 120-kVp patients than in the 100- and 80-kVp patients (29.9±3.1 vs. 26.1±3.1 vs. 22.7±2.0; p<0.0001). Retrospective protocols were used in 10.5%, 10.8% and 18.2% for 120-, 100- and 80- kVp patients, respectively. Overall, a post-processing algorithm called adaptive statistical iterative reconstruction (IR 30%) was used in 58% of patients. The radiation doses were 3.3, 1.9 and 1.0 mSv for the 120-, 100- and 80-kVp protocols (p<0.0001 for both), respectively. When compared with the 120-kVp protocol, lower tube voltages with 100 and 80 kVp were associated with an increased signal, higher contrast and increased noise with resultant increase in the SNRs (10.7±3.2 vs. 12.2±3.6 vs. 12.2±3.2; p<0.0001) and CNRs (7.8±2.5 vs. 9.5±3.5 vs. 9.7±2.8; p=0.0002), respectively. Image quality showed no significant difference among the kVp groups (p=0.243). Conclusion: A tube voltage reduction from the standard 120-kVp to 100- or 80-kVp protocols provided a total dose saving of 42% or 67%, respectively, without sacrificing image quality. We should consider more widespread use of lower tube voltages for patients who undergo CCTA to minimize radiation exposure.

The purpose of this study is to conduct a systematic reivew of the efficiency of radiation protection (RP) training in minimising the radiation dose to both medical staff and patients. The literature search for the relevant articles was performed using five different databases which included Scopus, ScienceDirect, PubMed, Medline and ProQuest. The search covered English language publications in the period between 2000 and 2014. The search was also limited to peer-reviewed articles on human subjects and reporting patient doses, staff doses or both before and after RP training. The dose reductions were compared using percentage calculations. Ten articles met the inclusion criteria and were included in the study. Seven of these studies showed the value of the RP training by measuring the patient dose and the fluoroscopy time (FT) pre- and post-training, whereas the remaining two of the three studies focused on the occupational doses only and one reported patient and staff doses as well as the FT. After receiving training, a reduction was found in patient doses and FT with a mean and standard deviation of 49% ± 0.15 and 12% ± 0.15, respectively. Additionally, the analysis displayed an occupational dose reduction by a mean and standard deviation of 72% ± 0.14 after receiving training. This review shows the necessity and efficacy of RP training in order to provide a safer environment when utilising the fluoroscopic image-guided machines by medical staff working in the catheterisation laboratory.

Diffusion tensor imaging is being performed as part of routine clinical neuroimaging and for research purposes, often involving multiple centers and different vendors. In order to perform comparatively quantitative analysis of tensor metrics, tensor data must be of high quality and reproducible which requires documentation of scanner stability, minimization of artifacts, and optimization and standardization of image parameters. We review various practical aspects of diffusion tensor imaging which impact quality of DTI with the focus on the quantification of diffusivities and fractional anisotropy.