Effect of CT acquisition parameters in the detection of subtle hypoattenuation in acute cerebral infarction: a phantom study

BACKGROUND AND PURPOSE

We evaluated the effects of varying tube voltage, current per rotation, and section thickness on detectability of 2- and 4-Hounsfield unit (HU) differences on brain CT between normal and ischemic gray matter within 6 hours of ischemia onset, by using a low-contrast phantom.

METHODS

The phantom with an attenuation of 36 HU corresponding to normal gray matter contained 2 sets of spheres (34 HU and 32 HU) corresponding to the early CT signs of ischemic brain and complete infarction, respectively. The reproducibility of the CT numbers and the contrast-to-noise ratio (CNR), defined as the CT number difference between the background (36 HU) and the spheres (34 HU or 32 HU) divided by the SD of the background CT number were measured. Five radiologists rated the phantom images for detection of the low-contrast spheres by visual inspection.

RESULTS

The CT numbers were reproducible within 1 HU with a tube current of > or =150 mAs at 120 kVp. The CNRs for the 34- and 32-HU spheres were positively correlated with the tube voltage, tube current per rotation, and the section thickness. A CNR of 1.0 was obtained for the 34-HU sphere when scanning was conducted with a section thickness of 10 mm at 120 kVp and 700 mAs, or 135kVp and 450 mAs, respectively. A significant improvement of the accuracy of detection was found with increasing tube current, tube voltage per rotation, and section thickness.

CONCLUSION

Our study indicated that the 2-HU hypoattenuation corresponding to the early CT sign of acute ischemic stroke can be detected by using appropriate parameter settings.

MR-based three-dimensional presentation of cartilage thickness in the femoral head

The purpose of our study was to visualize the hyaline cartilage of the femoral head and to evaluate the distribution of the thickness by three-dimensional reconstruction of MRI data. The MRI was performed in 10 normal volunteers, 1 patient with osteonecrosis and 4 with advanced osteoarthritis. A fast 3D spoiled gradient-recalled acquisition in the steady state pulse sequence (TR 22 ms/TE 5.6 ms/no. of excitations 2) with fat suppression was used for data collection. Coronal and sagittal images were obtained with 3-mm effective slice thickness, 16-cm field of view (FOV) and 256x192 matrix. The MR images were reconstructed in three dimensions for evaluating the distribution of the cartilage thickness. In all normal volunteers, 1 patient with osteonecrosis and three advanced osteoarthritis, 3D reconstruction was successful, but in 1 case of osteoarthritis, 3D reconstruction failed because of the narrow joint space. In normal volunteers, the cartilage thickness is thickest in the central portion around the ligamentum teres (mean 2.8 mm). The medial portion and the lateral portion are almost of the same thickness (medial 1.3 mm, lateral 1.1 mm). In 3 cases of osteoarthritis, the cartilage became thinner in the lateral portions (<0.6 mm), but was unchanged in the central and medial portions. Three-dimensional reconstruction of MRI data is useful for evaluating the distribution of the cartilage thickness of the femoral head objectively.

Three-dimensional flow velocity quantification of Freestyle aortic stentless bioprosthesis by magnetic resonance imaging: surgical consideration

The characteristics in flow dynamics of stentless bioprosthetic valve implanted in aortic position has been reported using Doppler echocardiography and beneficial results have been demonstrated in patients. Because some disturbed flow characteristics were seen clinically with existence of pressure gradient, the nature of flow-velocity characteristics was evaluated in patients receiving Freestyle stentless aortic bioprosthesis using new three-dimensional MRI method. In 19 patients after AVR with Freestyle bioprosthesis, flow-velocity study was conducted using velocity-encoding phase-contrast magnetic resonance imaging (MRI). Three-dimensional flow profiles were reconstructed. The implantation techniques were subcoronary (SC) in 10, root inclusion (Incl) in 6, and full root (FR) in 3 patients. These results were compared to 4 pts with stented bioprosthesis and 4 healthy volunteers. In 3-D flow velocity profiles, there were variations from almost normal pattern to some disturbed flow pattern. All patients of FR showed the parabolic flow pattern nearly equal to normal subjects. Over half of the patients with SC and Incl showed disturbed flow pattern with increased pressure gradient. Although hemodynamically acceptable, Freestyle aortic bioprosthesis showed some degree of flow disturbance in subcoronary or inclusion method with increased transvalvular velocity that may cause late problems, and these findings evaluated by 3-D method should be implicated in surgical consideration.

Quantitation of flow in the superior sagittal sinus performed with cine phase-contrast MR imaging of healthy and achondroplastic children

BACKGROUND AND PURPOSE

Cine phase-contrast (PC) MR imaging is a convenient and effective method for measuring volumetric flow rates in vivo. We attempted to evaluate changes in blood flow in the superior sagittal sinus (SSS) in children and to assess the hypothesis that restricted venous outflow attributable to stenosis of the jugular vein causes hydrocephalus in achondroplasia.

METHODS

Blood flow in the SSS was measured by using cine PC MR imaging with a 1.5-T scanner. After validation, 35 neurologically healthy children as well as eight children with achondroplasia (five with hydrocephalus) and two children with obstructive hydrocephalus were studied. Average flow velocity over the cardiac cycle and volumetric flow rate in the SSS were obtained. The data for healthy children were plotted as a function of age, and reference values were defined by using a five-point smoothing.

RESULTS

In healthy children, flow velocity ranged from 92 to 196 mm/s (mean, 136), and flow rate from 189 to 688 mL/min (mean, 484). The flow rate showed changes statistically related to age. It rapidly increased during the first 2 years and reached a peak by 6 to 8 years of age. The flow velocity showed a similar pattern, but not with significant correlation. In all cases of achondroplasia with hydrocephalus, both flow values were reduced below the reference values minus one standard deviation. In cases of achondroplasia without hydrocephalus, and in obstructive hydrocephalus, the values were not reduced.

CONCLUSION

Blood flow in the SSS reflects brain maturation. Hydrocephalus associated with achondroplasia was found to be closely related to reduced flow in the SSS, which supports the hypothesis that restricted venous outflow causes hydrocephalus in cases of achondroplasia.

[Usefulness of enhanced MR angiography by nitroglycerin]

We tried to use nitroglycerin to enhance MR angiography (MRA). Nitroglycerin has an effect to dilate vessels. We made a direct comparison between pre and post enhanced MRA (3 D-TOF technique). MRA after administration of nitroglycerin could depict more details of cortical branches without enhancement of background. So we recommend this method to be used in any examination of MR angiography.

Diurnal changes in vasopressin and oxytocin levels in cerebrospinal fluid of post-operative patients with intracranial aneurysms

Diurnal changes in vasopressin and oxytocin levels in cerebrospinal fluid were investigated under normal diurnal conditions. The patients examined had ruptured intracranial aneurysms, and underwent neck-clipping operations and continuous drainage from the basal cistern. All of the patients recovered consciousness without signs of neurological deficit. The investigations were conducted for 2 days starting 5-9 days after the neck-clipping operations were performed. The oxytocin concentration decreased as night fell, remained low during this period and then increased during the day. The vasopressin level demonstrated no definite rhythmic tendency. No correlation was revealed between the changes in the concentrations of either vasopressin or oxytocin in the cerebrospinal fluid and the osmolality.

Fluid blood density level demonstrated by computerized tomography in pituitary apoplexy. Report of two cases

✓ Two cases of pituitary apoplexy are presented. A fluid blood density level was demonstrated by computerized tomography in a suprasellar ring-enhancing lesion.