Applications of dual energy CT in clinical practice: A pictorial essay.

In dual-energy CT (DECT), two different x-ray spectra are used to acquire two image datasets of the same region, to allow the analysis of energy-dependent changes in the attenuation of different materials. Each type of material demonstrates a relatively specific change in attenuation between images obtained with a high-energy spectrum and those obtained with a low-energy spectrum. Based on the relatively specific change in attenuation with two different energies, material composition information can be obtained to allow tissue characterization. The DECT ability of material differentiation allows bone removal in various CT angiography studies and bone marrow edema depiction, while with material optimization, metal artefacts can be significantly reduced to almost nil. DECT allows material separation to differentiate uric acid crystals from calcium to determine the composition of urinary calculi and to diagnose gout. Using the DECT ability of material decomposition, iodine maps can be generated, which are useful in the evaluation of any enhancing lesion in the body without the need to obtain a plain scan and allow perfusion maps to be created in cases of pulmonary thromboembolism.

Steady-state MR imaging sequences: physics, classification, and clinical applications.

Steady-state sequences are a class of rapid magnetic resonance (MR) imaging techniques based on fast gradient-echo acquisitions in which both longitudinal magnetization (LM) and transverse magnetization (TM) are kept constant. Both LM and TM reach a nonzero steady state through the use of a repetition time that is shorter than the T2 relaxation time of tissue. When TM is maintained as multiple radiofrequency excitation pulses are applied, two types of signal are formed once steady state is reached: preexcitation signal (S-) from echo reformation; and postexcitation signal (S+), which consists of free induction decay. Depending on the signal sampled and used to form an image, steady-state sequences can be classified as (a) postexcitation refocused (only S+ is sampled), (b) preexcitation refocused (only S- is sampled), and (c) fully refocused (both S+ and S- are sampled) sequences. All tissues with a reasonably long T2 relaxation time will show additional signals due to various refocused echo paths. Steady-state sequences have revolutionized cardiac imaging and have become the standard for anatomic functional cardiac imaging and for the assessment of myocardial viability because of their good signal-to-noise ratio and contrast-to-noise ratio and increased speed of acquisition. They are also useful in abdominal and fetal imaging and hold promise for interventional MR imaging. Because steady-state sequences are now commonly used in MR imaging, radiologists will benefit from understanding the underlying physics, classification, and clinical applications of these sequences.

Acute calcific retropharyngeal tendinitis.

Knowledge of the characteristic clinical spectrum and imaging features of this disorder are crucial for a correct diagnosis of this uncommon cause of odynophagia and dysphagia.

Holding versus seeing pathology. Three-dimensional printing of the bony pelvis for preoperative planning of a complex pelvis fracture: A case report.

Pelvic injuries are not uncommon. The complex anatomy of the pelvic bones, the complex pattern of injuries, associated important structures such as neurovascular bundles, and difficult access make the reduction and fixation of these fractures difficult. Often the surgical outcomes are not satisfactory. Three-dimensional (3D) imaging using computed tomography (CT) scan (3DCT) has been the mainstay of preoperative evaluation since the 1980s, however, even with these images it may be difficult to understand complex injury patterns. Preoperative printing of a 3D model using the same CT scan data allows surgeons to hold the pelvis in their hands and then plan appropriate treatment. We report one such case of complex pelvic injury and its management using the novel method of preoperative 3D model printing.

Krabbe disease: unusual MRI findings.

We present the MRI findings in a case of infantile-onset Krabbe disease. Enlargement of the intracranial optic nerves and cervical cord were detected in addition to more typical changes in the cerebral white matter and thalami. We also review the proton MR spectroscopic findings in Krabbe disease.

MRI and ultrasound in solitary muscular and soft tissue cysticercosis.

Solitary cysticercosis of muscles and soft tissue is a rare disease and can cause a diagnostic dilemma clinically. We present the MRI and ultrasound findings in six patients with solitary muscular and soft tissue cysticercosis. Five of them had clear cysts that displayed low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Four of these cysts had scolices within them. One patient had an ill-defined hyperintense lesion on T2-weighted images without any clear cyst. Ultrasound performed in all patients showed similar findings, with the scolices being more clearly appreciated. MRI and ultrasound are useful in the diagnosis of solitary muscular and soft tissue cysticercosis and they reliably establish the diagnosis when a clear cyst with scolex is seen.