Lateral Topogram Research Articles

Dose-optimized computed tomography of the cervical spine in patients with shoulder pull-down: Is image quality comparable with a standard dose protocol in an emergency setting?

PurposeSuperimposing soft tissue and bony structures in computed tomography (CT) of the cervical spine (C-spine) is a limiting factor in optimizing radiation exposure maintaining an acceptable image quality. Therefore, we assessed image quality of dose-optimized (DO) C-spine CT in patients capable of shoulder pull-down in an emergency setting. Methods and materialsDO-CT (105mAs/120 kVp) of the C-spine in trauma settings was performed in patients with shoulder pull-down if C5 was not superimposed by soft tissue on the lateral topogram, otherwise standard-dose (SD)-CT (195 mAs/120 kVp) was performed. 34 DO (mean age, 68y ± 21; BMI, 24.2 kg/m2 ± 3.2) and 34 SD (mean age 70y ± 19; BMI 25.7 kg/m2 ± 4.4) iterative reconstructed CTs were evaluated at C2/3 and C6/7 by two musculoskeletal radiologists. Qualitative image noise and morphological characteristics of bony structures (cortex, trabeculae) were assessed on a Likert scale. Quantitative image noise was measured and effective dose (ED) was recorded. Parameters were compared using Mann-Whitney-U-test (p < 0.05). ResultsAt C2/3, DO-CT vs. SD-CT yielded comparable qualitative noise (mean, 1.3 vs. 1.0; p = 0.18) and morphological characteristics, but higher quantitative noise (27.2 ± 8.8HU vs. 19.6 ± 4.5HU; p < 0.001). At C6/7, DO-CT yielded lower subjective noise (1.9; SD-CT 2.2; p = 0.017) and better morphological characteristics with higher visibility scores for cortex (p = 0.001) and trabeculae (p = 0.03). Quantitative noise did not differ (p = 0.24). Radiation dose was 51% lower using DO-CT (EDDO-CT 0.80 ± 0.1 mSv; EDSD-CT 1.63 ± 0.2 mSv; p < 0.001). ConclusionC-spine CT with dose reduction of 51% showed no image quality impairment. Additional pull-down of both shoulders allowed better image quality at lower C-spine segments as compared to a standard protocol.

The relationship between CT scout landmarks and lung boundaries on chest CT: guidelines for minimizing excess z-axis scan length.

As the relationship between CT scout landmarks and chest CT boundaries is not known, the selected scan length is often greater than necessary for the CT scan, resulting in increased radiation dose to the neck and upper abdomen. The purpose of this study is to establish the relationship between CT scout landmarks with the superior and inferior boundaries of the lungs on chest CT. Retrospective comparison of the location of the top of the first rib on frontal scout and the most inferior costophrenic angle on lateral scout to the chest CT slice just above and below the lungs. The percent of scans that would exclude part of the lung based on CT initiated at several distances above or below these landmarks was calculated. There was 2.7 times greater variability between scout landmarks and lung boundaries inferiorly than superiorly on chest CT (p < 0.001). Initiating CT at the top of the first rib on scout did not exclude any lung on CT. Initiating CT 0, 1, 2, 3, and 4cm inferior to the CPA on lateral scout excluded part of the lung in 45.7%, 12.9%, 4.3%, 1.9%, and 0.8% of CTs. Chest CT to include the lungs should be performed from the top of the first rib to 3 or 4cm below the costophrenic angle on lateral topogram. • There is a greater motion at the inferior lung than at the superior lung. • Chest CT acquisition from the top of the first rib on scout would not exclude the lung. • Chest CT acquisition from CPA on lateral scout would exclude the lung 46% of time.

A completed audit cycle of the lateral scan projection radiograph in CT pulmonary angiography (CTPA); the impact on scan length and radiation dose

To investigate the effect of incorporating a lateral scan projection radiograph (topogram) in addition to the standard frontal topogram on excess scan length in computed tomography pulmonary angiography (CTPA) and to quantify the impact on effective dose. Fifty consecutive patients referred for exclusion of pulmonary embolism who had undergone a CTPA examination with conventional frontal topogram to plan scan length (protocol A) were compared with 50 consecutive patients who had undergone a CTPA study with frontal and additional lateral topogram for planning (protocol B) in a retrospective audit. Optimal scan length was defined from lung apex to lung base. Mean excess scan length beyond these landmarks was determined. The mean organ doses to the thyroid, liver, and stomach, as well as mean effective dose, were estimated using standard conversion factors. The mean excess scan length was significantly lower in protocol B compared to the protocol A cohort (19.5 ± 17.4 mm [mean ± standard deviation] versus 39.1 ± 20.4 mm, p < 0.0001). The mean excess scan length below the lung bases was significantly lower in the protocol B cohort compared to the protocol A group (7.5 ± 12.7 mm versus 23 ± 16.6 mm, p < 0.0001), as were the mean organ doses to the stomach (4.24 ± 0.81 mGy versus 5.22 ± 1.06 mGy, p < 0.0001) and liver (5.60 ± 0.64 mGy versus 6.38 ± 0.81 mGy, p < 0.0001). A non-significant reduction in over-scanning above the apices in protocol B was observed compared with protocol A (12 ± 8.8 mm versus 16.2 ± 13.6 mm, p = 0.07), which equated to lower mean thyroid organ dose in (3.28 ± 1.76 mGy versus 4.11 ± 3.11 mGy, p = 0.104). The present audit indicates that incorporation of a lateral topogram into the CTPA protocol, together with radiographer education, reduces excess scan length, which significantly reduces the dose to the liver and stomach, and potentially lowers the dose to the thyroid. This simple dose-saving technique can be applied to all CT investigations of the chest on all CT systems with immediate effect.

Does the incorporation of a lateral topogram reduce overscanning in CT pulmonary angiography (CTPA)?

Purpose: CTPA is a common investigation and its dose must therefore be minimised. Dose in CT can be reduced in several ways. Scan length is a simple parameter that can be optimised in all patients without compromising image quality.

SU‐FF‐I‐30: Generating Attenuation‐Based Tube Current Modulation (TCM) Schema Based On Voxelized Patient Models to Be Used in Simulations Estimating Organ Dose From CT

Purpose: There are several TCM algorithms in CT acquisition currently used including x‐y plane modulation, z‐axis only modulation and combined (x,y,z) modulation techniques. While these have been used to reduce radiation dose in general, methods do not yet exist to assess their impact on reducing organ dose. This study establishes a generalizable process to generate TCM schema from various attenuation‐based algorithms for use in Monte Carlo simulation methods to assess organ dose from voxelized patient models. Methods and Materials: A previously validated scanner‐specific Monte Carlo‐based CT scanner model was altered to allow simulation of a topogram with the x‐ray tube held at an assigned gantry angle. An Anterior‐Posterior (AP) and a Lateral topogram were simulated on a voxelized patient model. A cylindrical mesh tally was used to calculate attenuation for every slice location along the cranial‐caudal direction of the patient and for angular increments around the gantry of the patient. A plot of patient attenuation versus table position was obtained for both topograms. The ideal TCM was calculated for each table position and the entire three‐dimensional TCM schema was generated by interpolating between the ideal TCM plots to maintain smooth tube current transitions for the remainder of the gantry rotation. Results: Using this generalizable model, we were able to generate the attenuation‐based TCM schema for a voxelized patient model. Conclusion: The results of this study demonstrate the ideal TCM schema for a specific TCM algorithm, but this generalizable model can be used to generate the ideal TCM schema for any combination of gantry angle, table location, and width of detector data. Therefore, this generalizable model can be used to generate TCM schema based on all types of attenuation‐based TCM algorithms and for any voxelized patient model.

SU‐FF‐I‐107: Improving the Accuracy of CT Topograms for Node Localization in Breast Lymphoscintigraphy

Purpose: To characterize and compensate for fan‐beam distortion of a CT topogram, thereby improving a technique for localization using planar lymphoscintigram/topogram fusion by minimizing misregistration between modalities. Method and Materials: We are currently investigating the feasibility of fusing planar scintigrams and CT topograms as a means of localization for breast lymphoscintigraphy and determined a maximum expected lateral offset between modalities of ±2.8 cm for an average size patient. The spatial distortion due to the fan‐beam of the topogram is linearly related to offset from isocenter, suggesting the possibility of rescaling the topograms used for localization. In this work, we have adjusted the anterior topogram by determining the location of the node in the lateral scintigram and using the distance above or below isocenter to apply the appropriate magnification to the topogram so that it is correctly scaled for the plane of the node (vice versa for the lateral topogram). An IDL program [ITT Visual Information Solutions, Boulder CO] was written to facilitate the modification of the topograms; the program was tested with a data set of an anthropomorphic thorax phantom acquired using a hybrid SPECT/CT camera [Symbia®, Siemens Medical Solutions USA, Hoffman Estates IL]. Registration was visually assessed by fusing the scintigram with the original topogram, with the modified topogram, and with the fullthickness coronal‐projection CT to verify the localization. Results: The IDL program has been executed and is successfully modifying topograms to minimize distortion. The visual comparison of the scintigram/modified topogram and scintigram/full‐thickness coronal‐projection CT demonstrates less than ±0.34 cm offset. Conclusion: Appropriately magnified CT topograms have been generated and fused with planar scintigrams that have potential for producing images with improved anatomic localization for breast lymphoscintigraphy compared to the standard‐of‐care Co‐57 sheet source backlighting method. Conflict of Interest: Research sponsored by Siemens Medical Solutions USA.

Sphenoid sinusitis in children

The sphenoid sinus is the least accessible of all paranasal sinuses. Symptoms of involvement are often vague and nonlocalizing. Computed tomographic studies provide the best view of this sinus and its involvement with the disease process. At the same time, the potential for intracranial and intraorbital complications can be evaluated. These images, particularly the lateral topogram, provide a road map for safe entrance into the sinus. The transnasal approach is the most direct method of entry into the sphenoid sinus, and when the radiological studies are combined with a thorough knowledge of the three-dimensional anatomy of the area and careful surgical technique, safe sphenoid surgery can be performed.

Abschätzung der effektiven Dosis bei Knochenmineralmessungen mit Photonenabsorptiometrie und Computertomographie

There is still some uncertainty in the assessment and comparison of patient dose which results from bone mineral measurements on the lumbar spine by photon absorptiometry and x-ray computed tomography (CT). In the literature, skin dose values are offered in almost all cases. These are not meaningful, however, as the size of the irradiated volume and the radiation sensitivities of the respective organs are not taken into account. Here, the concept of effective dose has to be applied. An assessment of effective dose resulted in approximately 1 mu Sv for absorptiometry and approximately 30 mu Sv for computed tomography with low kV and mAs values. For lateral lumbar spine films which are often taken in connection with absorptiometry, at least 700 mu Sv have to be added. In CT, additional 30 mu Sv result from the lateral topogram which is required for positioning. The concept of effective dose, the data and assumptions used in its assessment and a comparison to other risk factors, as for example natural background radiation of approximately 2400 mu Sv per year, are discussed in detail.

Obstetric pelvimetry using digital radiography (CT topogram)

Radiographic examination during pregnancy and pelvimetry before pregnancy are still required for particular indications. The use of digital radiography (lateral topogram on CT) reduces the radiation dose to the foetus and ovaries by a factor of 10 to 100, as compared with conventional pelvimetry, as described by Guthmann. The accuracy of this method is satisfactory, the technique is simple, it is rapid and is easy for the patient, particularly for pregnant women. As long as pelvimetry is not possible without ionising radiation, we consider pelvimetry with digital radiography, when strictly indicated, to be acceptable. In order to determine the transverse diameter of the pelvis, a single additional CT cut through the narrowest part of the pelvis is suggested.

A low-dose CT-pelvimetry.

The suitability of CT for pelvimetry was studied. For accurate measurement of the true conjugate and interspinous diameter, a lateral topogram and an axial CT slice were taken. The radiation dose was reduced from 1 mGy (in conventional system) to 0.1-0.2 mGy.