Jonas Rydberg

Fundamentals of multichannel CT

Multichannel computed tomography (MCCT) has created a technical revolution in CT scanning. Following the introduction of single-channel helical scanning in 1989, 4-channel systems were introduced in 1998 and 16-channel systems in 2002. The core of this new technique is the X-ray detector array design, which allows for multiple simultaneous registration of slice information during gantry rotation. This design allows for faster scanning and acquisition of thinner slice widths. The high-speed scanning also minimizes motion artifacts. The ability to scan with very thin slice thickness creates a scanned volume with isotropic voxels. This allows for two- and three-dimensional reconstructions with similar resolution as the source images. MCCT also allows for higher X-ray tube currents, which create better penetration of metallic orthopedic fixation devices. Musculoskeletal imaging benefits from MCCT because large anatomic areas may be covered with thin slices. When needed, high tube currents can be applied for scanning areas of interest in the presence of metal. Thin slice acquisition allows isotropic viewing, which we use routinely.

Novel method for reducing high-attenuation object artifacts in CT reconstructions

A new method to reduce the streak artifacts caused by high attenuation objects in CT images has been developed. The key part of this approach is a preprocessing procedure based on the raw projection data using an adaptive scaling-plus-filtering method. The procedure is followed by the conventional filtered-back projection to reconstruct artifact-reduced images. Phantom and clinical studies have demonstrated that the proposed method can effectively reduce the streak artifacts caused by high attenuation objects for different anatomical structures and metal materials while still faithfully reproduce the positions and dimensions of the metal objects. The visualization of tissue features adjacent to metal objects is greatly improved. The proposed method is computational efficient and can be easily adapted to the current commercial CT scanners.

Low radiation dose ECG-gated chest CT angiography on a 256-slice multidetector CT scanner

Computed tomography angiography (CTA) of the thorax other than cardiac CTA, is utilized for a multitude of conditions and ranges in application from a diagnostic test, to presurgical planning and postsurgical follow-up. Helical CTA without electrocardiogram (ECG) gating has been routinely utilized for the evaluation of thoracic vasculature. However, its applicability can be limited in the evaluation of the thoracic aorta and pulmonary vasculature because of the artifacts resulting from cardiac motion. Traditional retrospective ECG-gated helical scans address this issue but at the price of a high radiation dose to the patient. In this paper we review CTA dose reduction strategies for non-coronary indications, examine field of view requirements, and discuss breath hold challenges for ECG-gated acquisitions. In addition, we present clinical examples performed using low-dose prospective gating technique for evaluation of the aorta acquired on a 256-slice multidetector computed tomography system.

Routine isotropic computed tomography scanning of chest: Value of coronal and sagittal reformations

Objective: We sought to evaluate the usefulness of coronal and sagittal reformations from isotropic chest computed tomography (CT) examinations. Methods: A total of 30 chest CT examinations were reconstructed into 2 sets of axial source images: 0.9-mm slice width with 0.45-mm reconstruction interval (isotropic) and 4-mm slices with 3-mm reconstruction interval. The isotropic dataset was reformatted into coronal and sagittal stacks with 4-mm slices. Three readers reviewed the image sets with 4-mm slice widths. Coronal and sagittal reformations were compared at the same sitting to axial images for depiction of anatomy and disease in the aorta, pulmonary arteries, hilar regions, mediastinum, lung parenchyma, pleura, diaphragm, thoracic spine, ribs, and trachea. A 5-point scale was used to determine whether nonaxial reformations showed anatomy and disease significantly better, somewhat better, same, somewhat worse or significantly worse than equivalent thickness axial source images. A 3-point scale was used to score if nonaxial image sets showed no, some, or significant additional information compared with the axial plane regarding the main diagnosis. Results: There was better visualization of the hilar regions, diaphragm, spine, and trachea on the coronal reformations compared with source axial images (P < 0.05). Sagittal reformations scored better than axial source images for aorta, pleura, diaphragm, spine, and ribs (P < 0.05). The coronal and sagittal series showed significant additional information in 11% and 9% of patients, respectively. Conclusion: Radiologists should consider the use of one or both of coronal and sagittal planes in addition to the axial series in routine interpretation of chest CT.

Accuracy of contrast-enhanced MDCT and MRI for identifying the severity and cause of neural foraminal stenosis in cervical radiculopathy: A prospective study

OBJECTIVE The purpose of this study was to determine the accuracy of IV contrast-enhanced MDCT and MRI for evaluation of the severity and cause of neural foraminal stenosis in patients with cervical radiculopathy. SUBJECTS AND METHODS Eighteen patients with cervical radiculopathy prospectively underwent contrast-enhanced MDCT and MRI. Contrast-enhanced MDCT scans were acquired at 1-mm thickness and reconstructed in oblique axial (parallel to disk) and sagittal (perpendicular to neural foramen) 2-mm sections without a gap. The MRI sequences used were sagittal T1-weighted, fast spin-echo T2-weighted, 3D fast spin-echo T2-weighted, axial T2-weighted, and 3D gradient-recalled echo. Three neuroradiologists independently and blindly rated the severity and cause of neural foraminal stenosis on a 4-point scale. Using the same scale at surgery, one of three surgeons rated the severity and cause of neural foraminal stenosis, and the results were used as the reference standard. Interobserver and intraobserver agreement (kappa) was calculated. RESULTS For severity of neural foraminal stenosis, the sensitivities of contrast-enhanced MDCT (50/55, 91%) and MRI (55/57, 96%) were similar, as were their specificities (contrast-enhanced MDCT, 13/24, 54%; MRI, 11/24, 46%). For cause of neural foraminal stenosis, the accuracies of contrast-enhanced MDCT (46/54, 85%) and MRI (45/57, 79%) were similar. Interobserver agreement on severity of neural foraminal stenosis was moderate to almost perfect for contrast-enhanced MDCT (kappa=0.50-1.00) and MRI (kappa=0.43-1.00). For cause of neural foraminal stenosis, interobserver agreement was moderate to substantial for contrast-enhanced MDCT (kappa=0.52-0.76) but only fair for MRI (kappa=0.23-0.39). Intra observer agreement was very high for severity of neural foraminal stenosis (contrast-enhanced MDCT, kappa=0.85; MRI, kappa=0.80) and cause of neural foraminal stenosis (contrast-enhanced MDCT, kappa=0.86; MRI, kappa=1.00). CONCLUSION Contrast-enhanced MDCT is as accurate as MRI in evaluation of the severity and cause of neural foraminal stenosis and may have better interobserver agreement.

Pathologic Characteristics of Exophytic Renal Masses

OBJECTIVE Pathologic grade is an important prognostic factor for renal-cell carcinoma (RCC). The objective of this study was to determine if there is any association of radiologic characteristics with pathologic grade and type of small renal tumors. PATIENTS AND METHODS We retrospectively reviewed the records of 500 patients who underwent extirpative renal surgery. Fifty-one patients met the inclusion criteria of solitary RCC <6 cm and adequate radiologic imaging available for review. The axial images with the largest area of tumor growing into the kidney were evaluated by a single radiologist to determine the percent of tumor that was exophytic. RESULTS Nine patients had tumors that were >67% exophytic, and 42 patients had tumors <67% exophytic. There is a statistically significant difference in the mean Fuhrman grade for these 2 groups (1.78 v 2.25, P < 0.01). The distribution of histologic subtype was as follows: 34 patients with clear cell, 15 with papillary, and one each with chromophobe and unclassified tumors. Papillary RCC comprised 78% (7 of 9) of tumors that were >67% exophytic and 15% (3 of 20) that were <33% exophytic. The relative risk of a >67% exophytic tumor being papillary v nonpapillary is 4.1. CONCLUSIONS Exophytic renal tumors are more likely to be of lower pathologic grade and of the papillary RCC subtype when compared with endophytic renal tumors. A larger prospective study is required to confirm these findings and determine the implications. This information may be useful when small tumors are being considered for watchful waiting or ablative therapies.