Effective dose and image quality evaluations of an automatic CT tube current modulation system with an anthropomorphic phantom

Abstract

The purpose of this study was to evaluate the consequences of different choices of acquisition parameters on the actual image noise and on the patient dose with an automatic tube current modulation system. The CT investigated was a GE Lightspeed 16-slice and an anthropomorphic phantom was used to simulate the patient. Several acquisitions were made varying noise index (NI), kilovoltage and pitch values. Tube current values were compared for the different acquisitions. Patient dose was evaluated in terms of volumetric computed tomography dose index (CTDI(vol)) and also as effective dose. The noise actually present in the images was analyzed by a region of interest analysis considering representatively phantom sections in the regions of the shoulders, of the lungs and of the abdomen. The obtained results generally evidenced a good agreement between the noise index and the measured noise for the abdomen sections, whereas for the shoulders and the lungs sections the measured noise was respectively greater and lower of the NI. Varying the kV the automatic current modulation system provided images with a substantially constancy of the actual noise and of the patient dose. An increase of the pitch generally decreased the patient dose, whereas the noise was slightly greater for the lowest pitch and almost constant for the other pitch values. This study outlines some important relationships between an automatic tube current modulation system and other CT acquisition parameters, providing useful informations for the choice requested by radiologists in the task of optimization of the CT acquisition protocols. Unless there are other considerations in place, pixel pitches below 1.375 should be avoided, and kVp settings can be changed with no real impact on dose or image noise.

Patient doses in CT examinations in Switzerland: implementation of national diagnostic reference levels

“…reduced tube voltages of 80-100 kV and thus reduced doses compared with standard settings of 120 kV (16,17) . Statistical analysis for lumbar spine CT resulted in a DRL of 30 mGy for CTDI vol and 850 mGy .…”

Doses em tomografia computadorizada de crânio: impacto do uso do controle automático de exposição

“…A otimização de outros parâmetros, como a utilização de um pitch maior, possibilitou reduções de dose de 44% utilizando o AEC para pacientes adultos 8 .…”

“…Diversos estudos tem demostrado que o uso do controle automático de exposição ou AEC (Automatic Exposition Control) [7][8][9] e/ou modificações na tensão do tubo de raios X, pitch 10 e espessura do corte, podem reduzir a dose no paciente, sem afetar significativamente a qualidade da imagem 11 .…”

Estimated Radiation Exposure from Medical Imaging in Hemodialysis Patients

“…The tube current values for all of the acquired scans were recorded after extracting the information from the DICOM header of the stored images by means of an automatic routine. 38 These values were multiplied by the rotation time used to obtain the milliampere time second values. The volumetric CT dose index provided by the equipment user interface was recorded for every exposure condition.…”

“…The software ImPACTCTPATIENTDOSECALCULATORv1.02(ImPACT,London,UK) was used after a modification of the calculation procedure to consider the actual distribution of organ doses consequent to the tube current modulation. 38 Briefly a Microsoft Excel macro was developed that considers the milliampere current values for every slab of thickness 1 cm of the scanned volume; it calculates the relative effective dose contribution and adds all of the contributions to determine the total effective dose. To err on the side of underestimating exposure, a value of 14.0 mSv was assigned to each complete abdomen-pelvis scan irrespective of the acquisition protocol adopted (routine or vascular).…”