| Objective The temporal bone was scanned with SOMATOM Sensation 64-slice spiral CT in different tube current and pitch. We compare image quality of multi-planar reformation of different dosages in order to evaluate the effect of low dose temporal MSCT on normal structures display and image quality, and to study the feasibility and clinical significance of 64 slice spiral CT low dose scanning in the examination of the temporal bone.Methods Using SOMATOM Sensation 64-slice spiral CT system and the same CT technique and inner ear protocol as those used for clinical CT, the five cranium specimens (ten ears), which is selected from anatomy department of Shandong university, were scanned with Scanning parameters as follows: 120 kV, 20×0.6 mm collimator, 200 mm FOV, 512×512 Matrix, 1 s/r, 0.6 mm nominal slice width. Firstly, when pitch=0.8, the different tube current (380, 300, 200, 160, 120, 80) were applied, Secondly, When mA=380, the different pitch (0.8, 1.0, 1.2) was adopted. The raw data was processed by using axial, coronal and double oblique multi-planar reformation; Images obtained were graded in terms of quality with a 5-point scale(5=excellent, 4=good, 3=fair, 2=poor, and 1=nondiagnostic). In grading image quality at axial MPR, The radiologic specialists focused on the subarcuate fossa, tendon of tensor tympani, facial recess, vestibular aqueduct and pyramidal eminence, In grading image quality at coronal MPR, attention was given to the scute, crista transversa, fenestra cochleae, lateral malleal ligament and snake eyes signature of cranial nerve, In the grading of the image quality at double oblique MPR, the radiologic specialists concentrated on the malleus, incus, stirrup bone, upper bony semicircular and aquaeductus fallopii, and then to implement statistical analysis. In order to choose the minimum tube current values and the maximum pitch that can satisfy the diagnosis request, image quality of axial, coronal and double oblique reformation images was compared with different tube current groups. 15 ears of volunteers were used to test the validity with the scanning parameter. Subsequently noise, MTF and dose length product were measured by phantoms in different tube current and pitch, the parameters obtained were compared and taken into statistics analysis.Results (1) Mean radiation dose was conspicuously reduced from 0.68 mSv (380mA) to 0.36 mSv (200 mA). No significant difference of anatomic structures display between the two tube current protocols. The result of scores was no significant statistics difference when pitch increased from 0.8 to 1.2, and the dosages don't change with the pitch. (2) The image parameters were compared. The image noise increased along with descent of tube current, but don't vary with increment of pitch, spatial resolution don't vary with the pitch and tube current.Conclusions Decreasing tube current appropriately in 64-slice spiral CT,the background noise of image increased, but the anatomy of the temporal bone was not influenced. So in this way the patients were protected effectively as the dose decreased obviously and the request of diagnosis can be satisfied. In addition, the radiation dosages don't decrease with increment of the pitch because of the auto-pitch modulation technology, but the scanning time is shortened.
|
PDF Full Text Request