Which are advantages of PA projection over AP projection of the lumbar spine?

The effect of erect abdomen radiography on absorbed doses to internal organs and tissues: A clinical study

2022, Journal of Medical Imaging and Radiation Sciences

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As low as reasonably achievable principles (ALARA) should be applied during all X-ray examinations. In some institutions, an acute abdomen series includes both erect and supine radiography. The purpose of the study was to evaluate the effect of an erect position on absorbed dose to internal abdominal organs when compared with the supine position.

A prospective study was undertaken where 81 patients were imaged in both supine and erect positions. The PCXMC Monte Carlo software was used to estimate individual organ doses using dose area product (DAP). Absorbed doses were calculated for the large intestines, active bone marrow, liver, lungs, small intestine, stomach, gallbladder, breasts, uterus, ovaries, urinary bladder, kidneys, testicles, and prostate.

The results showed a significant increase of absorbed dose by 1.4% when moving from a supine to an erect position. The testes were found to be the organs most affected by the erect position and then the urinary bladder.

According to the study's findings, using the erect position during abdominal radiography increases the radiation dose for all of the selected organs compared to using a supine position. Therefore, it is advised that the use of erect abdomen radiography be restricted to certain circumstances.

Le principe du niveau le plus bas qu'il soit raisonnablement possible d'atteindre (ALARA) doit être appliqué pendant tous les examens radiologiques. Dans certaines institutions, une série d'examens de l'abdomen aigu comprend à la fois des radiographies en position debout et en position couchée.

L'objectif de cette étude était d'évaluer l'effet de la position debout sur la dose absorbée par les organes abdominaux internes par rapport à la position couchée.

Une étude prospective a été entreprise dans laquelle 81 patients ont été imagés en position couchée et en position debout. Le logiciel PCXMC Monte Carlo a été utilisé pour estimer les doses individuelles aux organes en utilisant le produit dose-zone (DAP). Les doses absorbées ont été calculées pour le gros intestin, la moelle osseuse active, le foie, les poumons, l'intestin grêle, l'estomac, la vésicule biliaire, les seins, l'utérus, les ovaires, la vessie urinaire, les reins, les testicules et la prostate.

Les résultats ont montré une augmentation significative de la dose moyenne absorbée de 97% à 98,4% lors du passage de la position couchée à la position debout. Les testicules se sont avérés être les organes les plus affectés par la position debout, puis la vessie urinaire.

Selon les résultats de l'étude, l'utilisation de la position debout pendant la radiographie abdominale augmente la dose de rayonnement pour tous les organes sélectionnés dans l'étude par rapport à l'utilisation de la position couchée. Par conséquent, il est conseillé de limiter l'utilisation de la radiographie abdominale en position debout à certaines circonstance.

PA positioning significantly reduces testicular dose during sacroiliac joint radiography

2010, Radiography

Citation Excerpt :

They summarized that their results were different from other studies because they were using external protection, which is used in most of the radiology departments, and not the gonadal cup protection that is almost entirely wrapped around the male genitals.6 Nic an Ghearr and Brennan7 measured the difference to female patients in conventional abdominal examination. They discovered that the entrance surface dose (ESD) measured on the phantom in PA projection was 16% lower than the ESD in AP projection (p ≤ 0.09).

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Radiation dose to the testes in the antero-posterior (AP) and postero-anterior (PA) projection of the sacroiliac joint (SIJ) was measured with and without a scrotal shield. Entrance surface dose, the dose received by the testicles and the dose area product (DAP) was used.

DAP measurements revealed the dose received by the phantom in the PA position is 12.6% lower than the AP (p ≤ 0.009) with no statistically significant reduction in image quality (p ≤ 0.483). The dose received by the testes in the PA projection in SIJ imaging is 93.1% lower than the AP projection when not using protection (p ≤ 0.020) and 94.9% lower with protection (p ≤ 0.019). The dose received by the testicles was not changed by the use of a scrotal shield in the AP position (p ≤ 0.559); but was lowered by its use in the PA (p ≤ 0.058).

Use of the PA projection in SIJ imaging significantly lowers, the dose received by the testes compared to the AP projection without significant loss of image quality.

Impact of focal spot size on radiologic image quality: A visual grading analysis

2010, Radiography

Citation Excerpt :

The current study employed a visual grading analysis (VGA). This is a well proven method of analyzing the visualization of normal anatomic features12–18 and has shown a good ability to discriminate between test variables such as varying beam energy,21 novel radiographic techniques22,23 and rare-earth filters.14 It is acknowledged, however, that unlike a receiver operating characteristic (ROC) investigation, VGA testing does not assess diagnostic efficacy and, therefore, at this stage the impact of different focal spot sizes on the ability to detect abnormal lesions cannot be commented upon with confidence.

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Fine and broad focal spot sizes are available on general X-ray tubes. Excessive use of fine focus can impact on tube life and whilst it is established that fine focal spot size reduces geometric unsharpness, the extent of this benefit on clinical image quality is unclear.

The current cadaver-based work compares images produced with effective focal sizes of 0.8 mm and 1.8 mm. Four projection types were included, lateral ankle, antero–posterior (AP) knee, AP thoracic spine and horizontal beam lateral (HBL) lumbar spine, and a visual grading analysis was used to assess visibility of anatomical criteria. Five clinicians scored each image using a 1–4 scoring scale, a reference image was employed for standardization and a Mann–Whitney U statistical test compared results derived from each focus. Radiation doses were monitored using a dose area product (DAP) meter.

Statistical analyses demonstrated no significant differences between images produced at each focus, although a relationship between body part thickness and number of criteria with a higher (non-significant) score for the fine focus compared with the broad focal spot size was demonstrated. Choice of focus had no radiation dose implications.

Fine foci X-ray sources are used predominantly for extremity imaging to enhance visualization of fine detail such as trabecular patterns, yet there is no evidence to support this practice. The argument for regular employment of fine foci, particularly for the type of acquisition and display devices used in this study, needs to be revisited.

The effect of patient shield position on gonad dose during lumbar spine radiography

2010, Radiography

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In an effort to standardise radiological practices in the Republic of Ireland, current legislation states that “written protocols for every type of standard radiological practice shall be established”. In order to fulfil this requirement the Irish Medical Council recommends the protocols issued by the Commission of European Communitees (CEC) for adoption in the country. Whilst this document does provide good guidance with regard to various radiographic factors, patient shielding instructions are notably ambiguous. The aim of this study was to remove some of this ambiguity by defining the optimal method of positioning patient shielding in antero-posterior (AP) and lateral lumbar spine radiographic examinations. These projections were chosen on the basis of their area of coverage being in close to and in some cases including the reproductive organs. They also represent the highest source of collective population dose of any conventional radiographic examination carried out in the UK.

A dosimetry study was devised to establish organ dose to the male testes and female ovaries using various clinically advocated methodologies for positioning patient shielding these included: no apron; tube-side apron; receptor-side apron and a wrap-around apron. The study was carried out using a direct digital radiography unit, an anthropomorphic phantom, various lead aprons and lithium thermoluminescent dosimeters (TLD).

For the AP projection, a statistically significant testes dose reduction of 42% (p ≤ 0.01) was observed when a tube-sided apron was used. No testes dose reductions were noted for the lateral projection. Ovary dose savings were not observed for any of the shielding methods investigated.

This study found that the testes dose in AP examinations was reduced by 42% when patient shielding was positioned inferior to the imaged field and on the tube-side of the patient. This result validates the shielding methods used at the majority of centres surveyed in a recent study.

An examination of practice during radiography of the clavicle

2010, Radiography

Citation Excerpt :

It has been suggested that a PA projection would reduce the effective dose of the examination, reducing the risks to the patient undergoing the examination. Evidence8,9 and theory10,11 may suggest that PA positioning in radiography may reduce effective dose to the patient and result in equal or increased image quality.12 Before implementing any new technique, however, we must consider the implications and the practicality of positioning.

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Variation in techniques is a well reported phenomenon in Radiography that can lead to dose discrepancies. Radiography of the clavicle is an examination which can result in a scattered extra-focal radiation dose to the radiosensitive organs of the thyroid, breast and eyes. Techniques for imaging the clavicle are examined and causal factors of repeats examined. Given the recent increase of the tissue weighting factor of breast tissue, an increased importance is placed upon dose reduction techniques to this area.

This study aims to investigate the variation in techniques used in imaging of the clavicle and to investigate whether AP or PA position resulted in a higher level of repeat imaging.

To investigate current practice amongst hospitals a sample of large teaching hospitals was chosen (n = 5). An interview with radiographers was carried out along with an examination of the stated protocols in each of these hospital plus retrospective analysis of the images produced in each of these hospitals.

Variations in practice were established, significant differences in collimation and vertical centring were found. AP coned view of the clavicle was performed by 80% of radiographers interviewed with 20% of radiographers performing an AP shoulder. This variation being 100% correlated with country of training. 60% of radiographers were found to perform AP15° cranial angulation clavicle as a second projection with 28%, 8% and 4% of those interview performing AP25°, AP20°, and AP30° cranial angulation, respectively. The comparison of error and repeat rates study demonstrated a lack of confidence, reduced employment of collimation and reduced accuracy while centring in the PA position and it was deemed necessary to repeat in 30% of cases compared to 40% repeats were necessary.

Wide variation exists in technique and PA imaging is not being implemented. The author recommends training and information on PA technique be disseminated and the local protocols address variations in practice.

Optimisation of X-ray examinations: General principles and an Irish perspective

2009, Radiography

Citation Excerpt :

thirty two percent reduction in ESD reported for chest radiographs when carbon-fibre cassettes are used46; utilisation of a PA technique for radiography of the abdomen47 and lumbar spine48 has been recommended to reduce patient dose, resulting from the tissue displacement effect of the prone position and also the lower absorption in sensitive anterior organs when the patient is in the prone position. Consideration of the various investigations above highlights the complex inter-relationship that influence optimisation.

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In Ireland, the European Medical Exposures Directive [Council Directive 97/43] was enacted into national law in Statutory Instrument 478 of 2002. This series of three review articles discusses the status of justification and optimisation of X-ray examinations nationally, and progress with the establishment of Irish diagnostic reference levels.

In this second article, literature relating to optimisation issues arising in SI 478 of 2002 is reviewed. Optimisation associated with X-ray equipment and optimisation during day-to-day practice are considered. Optimisation proposals found in published research are summarised, and indicate the complex nature of optimisation. A paucity of current, research-based guidance documentation is identified. This is needed in order to support a range of professional staff in their practical implementation of optimisation.

Research article

Establishing Local Diagnostic Reference Levels in IR Procedures with Dose Management Software

Journal of Vascular and Interventional Radiology, Volume 28, Issue 3, 2017, pp. 429-441

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To obtain local diagnostic reference levels (DRLs) in diagnostic and therapeutic IR procedures with dose management software to improve radiation protection.

Dose data of various vascular and nonvascular IR procedures performed within 18 months were collected and analyzed with dose management software. To account for different levels of complexity, procedures were subdivided into simple, standard, and difficult procedures as graded by interventional radiologists. Based on these analyses, local DRLs (given as kerma-area product [KAP]) were proposed. Comparison with dose data of others was conducted, and Spearman correlation coefficients were calculated to evaluate relationships between dose metrics.

Analysis included 1,403 IR procedures (simple/standard/difficult, n = 346/702/355). Within the same procedure, KAP tended to increase with level of complexity. Overall, very strong correlation between KAP (Gy ∙ cm2) and cumulative air kerma (KA,R; Gy) was observed, and moderate to strong correlation between KAP and time and KA,R and time was observed. For simple procedures, strong correlation was seen between KAP and time and KA,R and time; for standard and difficult procedures, only moderate correlation was seen. Correlation between KAP and time and KA,R and time was strong in nonvascular procedures but only moderate in vascular procedures.

Dose management software can be used to derive local DRLs for various IR procedures, taking into consideration different levels of complexity. Proposed local DRLs can contribute to obtaining detailed national DRLs as part of efforts to improve patients’ radiation protection further.

Research article

Supine and erect abdominal radiography: A comparison of radiation dose and image quality

Applied Radiation and Isotopes, Volume 190, 2022, Article 110477

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Abdominal radiographs are often the first diagnostic imaging tool for patients with acute abdominal pain. In most cases, a supine X-ray is sufficient, but in some cases, an erect abdominal radiograph may be warranted and can provide additional benefits. The aim of this study was to compare erect and supine projections in terms of radiation dose and image quality.

Body mass index (BMI), sagittal body thickness, dose area product (DAP)and effective dose (ED) data were collected for 81 patients referred for digital abdominal radiography in both the supine and erect positions. The ED was estimated by inserting the dose area product (DAP) for each projection into the dose modelling computer software PCXMC 2.0. Image quality was assessed by both visual and quantitative methods.

The mean ± standard deviation (SD) ED was 0.4 ± 0.3 and 0.2 ± 0.1 mSv for erect and supine projections, respectively (p < 0.001). The estimated ED in the erect position was 102% higher compared to the supine position. The mean ± SD visual image quality was reduced (27%) when using an erect position 1.9 ± 0.5 when compared with supine 2.6 ± 0.7. The calculated signal to noise ratio (SNR) was higher in erect position by 14%. Contrast to noise ratio (CNR) was reduced by 16% when using an erect position.

Study findings support the continued use of the supine position as the preferred method due to significant reductions in radiation dose when compared to erect imaging. A single projection is likely to be sufficient but in certain situations, for example in case of absence of a computed tomography (CT) scanner or ultrasound, then an additional erect abdominal radiograph may be warranted.

The erect abdomen radiograph increases the radiation dose and decreases the image quality. Further research is required to define more holistically evaluation optimisation strategies to reduce the patient dose, such as using an increase source-to-image distance or the development of patient-specific exposure parameters for evaluating different clinical indications and patient sizes.

Research article

Radiation dose measurement for patients undergoing common spine medical x-ray examinations and proposed local diagnostic reference levels

Radiation Measurements, Volume 87, 2016, pp. 29-34

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The main purposes of this study were to investigate patient dose in Spine radiographic examinations, as high dose procedures and propose the first LDRLs (Local Diagnostic Reference Levels) in Khuzestan region, southwest of Iran. ESD (Entrance Skin Dose) values of patients who underwent six spine radiographic procedures containing cervical (AP/LAT), thoracic (AP/LAT) and lumbar (AP/LAT), as high dose procedures, were evaluated. Patient doses were calculated from patient's individual anatomical data (weight, height and organ thickness) and exposure parameters (kVp, mAs, FFD and projection) based on the IAEA (International Atomic Energy Agency) Technical Report Series No.457. Indirect dosimetry method was conducted on 412 standard patients (57% men and 43% women) at seven high-patient-load hospitals. This survey reveals significant variations in the radiological practice. Despite large discrepancies found in the tube loadings (3–128 for lumbar AP and 3–200 for lumbar LAT), ESDs in all examinations were lower than the IAEA and EC (European Commission) DRLs (Diagnostic Reference Levels), 1.30, 1.65, 2.29, 3.09, 5, 7.5 mGy for cervical AP, cervical LAT, thoracic AP, lumbar AP, thoracic LAT and lumbar LAT respectively. Optimization of radiological practice could be accelerated by updating clinical audits and patient dose considerations, adequate training of students, implementation of systematic QA and QC programs and the use of qualified diagnostic medical physicists in the imaging sections. It is advisable that DRLs obtained in this study can be used as local DRL and dose surveys must be performed in all regions to establish NDRLs (National Diagnostic Reference Levels) in Iran. Also, national authorities must review periodically reference levels to ensure that it remains appropriate.

Research article

Mammography screening: A major issue in medicine

European Journal of Cancer, Volume 90, 2018, pp. 34-62

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Breast cancer mortality is declining in most high-income countries. The role of mammography screening in these declines is much debated.

Screening impacts cancer mortality through decreasing the incidence of number of advanced cancers with poor prognosis, while therapies and patient management impact cancer mortality through decreasing the fatality of cancers. The effectiveness of cancer screening is the ability of a screening method to curb the incidence of advanced cancers in populations. Methods for evaluating cancer screening effectiveness are based on the monitoring of age-adjusted incidence rates of advanced cancers that should decrease after the introduction of screening. Likewise, cancer-specific mortality rates should decline more rapidly in areas with screening than in areas without or with lower levels of screening but where patient management is similar. These two criteria have provided evidence that screening for colorectal and cervical cancer contributes to decreasing the mortality associated with these two cancers. In contrast, screening for neuroblastoma in children was discontinued in the early 2000s because these two criteria were not met. In addition, overdiagnosis – i.e. the detection of non-progressing occult neuroblastoma that would not have been life-threatening during the subject's lifetime – is a major undesirable consequence of screening.

Accumulating epidemiological data show that in populations where mammography screening has been widespread for a long time, there has been no or only a modest decline in the incidence of advanced cancers, including that of de novo metastatic (stage IV) cancers at diagnosis. Moreover, breast cancer mortality reductions are similar in areas with early introduction and high penetration of screening and in areas with late introduction and low penetration of screening. Overdiagnosis is commonplace, representing 20% or more of all breast cancers among women invited to screening and 30–50% of screen-detected cancers. Overdiagnosis leads to overtreatment and inflicts considerable physical, psychological and economic harm on many women. Overdiagnosis has also exerted considerable disruptive effects on the interpretation of clinical outcomes expressed in percentages (instead of rates) or as overall survival (instead of mortality rates or stage-specific survival). Rates of radical mastectomies have not decreased following the introduction of screening and keep rising in some countries (e.g. the United States of America (USA)). Hence, the epidemiological picture of mammography screening closely resembles that of screening for neuroblastoma.

Reappraisals of Swedish mammography trials demonstrate that the design and statistical analysis of these trials were different from those of all trials on screening for cancers other than breast cancer. We found compelling indications that these trials overestimated reductions in breast cancer mortality associated with screening, in part because of the statistical analyses themselves, in part because of improved therapies and underreporting of breast cancer as the underlying cause of death in screening groups. In this regard, Swedish trials should publish the stage-specific breast cancer mortality rates for the screening and control groups separately. Results of the Greater New York Health Insurance Plan trial are biased because of the underreporting of breast cancer cases and deaths that occurred in women who did not participate in screening. After 17 years of follow-up, the United Kingdom (UK) Age Trial showed no benefit from mammography screening starting at age 39–41.

Until around 2005, most proponents of breast screening backed the monitoring of changes in advanced cancer incidence and comparative studies on breast cancer mortality for the evaluation of breast screening effectiveness. However, in an attempt to mitigate the contradictions between results of mammography trials and population data, breast-screening proponents have elected to change the criteria for the evaluation of cancer screening effectiveness, giving precedence to incidence-based mortality (IBM) and case—control studies. But practically all IBM studies on mammography screening have a strong ecological component in their design. The two IBM studies done in Norway that meet all methodological requirements do not document significant reductions in breast cancer mortality associated with mammography screening. Because of their propensity to exaggerate the health benefits of screening, case–control studies may demonstrate that mammography screening could reduce the risk of death from diseases other than breast cancer.

Numerous statistical model approaches have been conducted for estimating the contributions of screening and of patient management to reductions in breast cancer mortality. Unverified assumptions are needed for running these models. For instance, many models assume that if screening had not occurred, the majority of screen-detected asymptomatic cancers would have progressed to symptomatic advanced cancers. This assumption is not grounded in evidence because a large proportion of screen-detected breast cancers represent overdiagnosis and hence non-progressing tumours. The accumulation of population data in well-screened populations diminishes the relevance of model approaches.

The comparison of the performance of different screening modalities – e.g. mammography, digital mammography, ultrasonography, magnetic resonance imaging (MRI), three-dimensional tomosynthesis (TDT) – concentrates on detection rates, which is the ability of a technique to detect more cancers than other techniques. However, a greater detection rate tells little about the capacity to prevent interval and advanced cancers and could just reflect additional overdiagnosis. Studies based on the incidence of advanced cancers and on the evaluation of overdiagnosis should be conducted before marketing new breast-imaging technologies.

Women at high risk of breast cancer (i.e. 30% lifetime risk and more), such as women with BRCA1/2 mutations, require a close breast surveillance. MRI is the preferred imaging method until more radical risk-reduction options are eventually adopted. For women with an intermediate risk of breast cancer (i.e. 10–29% lifetime risk), including women with extremely dense breast at mammography, there is no evidence that more frequent mammography screening or screening with other modalities actually reduces the risk of breast cancer death.

A plethora of epidemiological data shows that, since 1985, progress in the management of breast cancer patients has led to marked reductions in stage-specific breast cancer mortality, even for patients with disseminated disease (i.e. stage IV cancer) at diagnosis. In contrast, the epidemiological data point to a marginal contribution of mammography screening in the decline in breast cancer mortality. Moreover, the more effective the treatments, the less favourable are the harm–benefit balance of screening mammography.

New, effective methods for breast screening are needed, as well as research on risk-based screening strategies.

Research article

Optimisation of the AP abdomen projection for larger patient body thicknesses

Radiography, Volume 28, Issue 1, 2022, pp. 107-114

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This study aims to identify optimal exposure parameters, delivering the lowest radiation dose while maintaining images of diagnostic quality for the antero-posterior (AP) abdomen x-ray projection in large patients with an AP abdominal diameter of >22.3 cm.

The study was composed of two phases. In phase 1, an anthropomorphic phantom (20 cm AP abdominal diameter) was repetitively radiographed while adding 3 layers (5 cm thick each) of fat onto the phantom reaching a maximum AP abdominal diameter of 35 cm. For every 5 cm thickness, images were taken at 10 kVp (kilovoltage peak) intervals, starting from 80 kVp as the standard protocol currently in use at the local medical imaging department, to 120 kVp in combination with the use of automatic exposure control (AEC). The dose area product (DAP), milliampere-second (mAs) delivered by the AEC, and measurements to calculate the signal to noise ratio (SNR) and contrast to noise ratio (CNR) were recorded. Phase 2 included image quality evaluation of the resultant images by radiographers and radiologists through absolute visual grading analysis (VGA). The resultant VGA scores were analysed using visual grading characteristics (VGC) curves.

The optimal kVp setting for AP abdominal diameters at: 20 cm, 25 cm and 30 cm was found to be 110 kVp increased from 80 kVp as the standard protocol (with a 56.5% decrease in DAP and 76.2% in mAs, a 54.2% decrease in DAP and 76.2% decrease in mAs and a 29.2% decrease in DAP and 59.7% decrease in mAs, respectively). The optimal kVp setting for AP abdominal diameter at 35 cm was found to be 120 kVp increased from 80 kvp as the standard protocol (with a 50.7% decrease in DAP and 73.4% decrease in mAs). All this was achieved while maintaining images of diagnostic quality.

Tailoring the exposure parameters for large patients in radiography of the abdomen results in a significant reductions in DAP which correlates to lower patient doses while still maintaining diagnostic image quality.

This research study and resultant parameters may help guide clinical departments to optimise AP abdomen radiographic exposures for large patients in the clinical setting.

Research article

Image quality assessment with dose reduction using high kVp and additional filtration for abdominal digital radiography

Physica Medica, Volume 50, 2018, pp. 46-51

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Dose reduction using additional filters with high kilovoltage peak (kVp) for abdominal digital radiography has received much attention recently. We evaluated image quality with dose reduction in abdominal digital radiography by using high kVp and additional copper filters at a tertiary hospital.

Between June 2016 and July 2016, 82 patients underwent abdominal digital radiography using 80 kVp in X-ray room 1 and 82 were imaged using 92 kVp with 0.1-mm copper filtration in X-ray room 2. The effective dose was calculated using a PC-based Monte Carlo program. Image quality of the abdominal radiography acquired in the two rooms was evaluated using a five-point ordinal scale, as well as the signal-to-noise and contrast-to-noise ratios.

The mean effective dose decreased by 25.8% and 25.7% for the supine and standing positions, respectively, when abdominal digital radiography using 92 kVp with 0.1-mm copper filtration was performed. In the 20 patients who performed abdominal digital radiography twice in each room, visual grading scores for visualisation of psoas outlines and kidney outlines are higher in room 1. However, there was no statistical significant difference of visual grading scores among the 124 patients who underwent only one abdominal radiography in the room 1 or 2 (P > 0.05).

Dose reduction for abdominal digital radiography can be achieved with comparable image quality by performing abdominal digital radiography using 92 kVp with 0.1-mm copper filtration, despite the higher AEC dose.

What is the advantage of PA lumbar to AP lumbar?

How can you tell the difference between AP and PA?

What is the best projection to demonstrate the lumbosacral joint?

Why is the AP projection of the thumb preferred over the PA projection?