Optimizing z-axis coverage of abdominal CT scans of the urinary tract: a proposed alternative proximal landmark for acquisition planning

Abstract

Objective: To evaluate an alternative method to reduce the acquisition coverage of urinary tract CT. Methods: This retrospective study included 365 abdominopelvic CT studies. Three radiographers simulated shortened acquisition coverages using three methods to determine the upper limit of the acquisition: Method 1 used the renal contours; Method 2 used the inferior margin of the 10th thoracic vertebra; and Method 3 used the point of intersection of the left diaphragmatic dome and the anterior margin of the vertebral bodies. Reductions in acquisition coverage and number of CT scans with a portion of the kidney excluded from the simulated reduced acquisition were compared between the three methods.Results: The mean 6 standard deviation reduction of acquisition coverage for the three readers with Methods 1, 2 and 3 were 20.5 6 4.8, 15.1 6 6.5 and 18.2 6 5.3%, respectively. Compared with Method 2, Method 3 allowed a mean scan length reduction of 3.6%. The proportions of CT scans with a portion of the kidney excluded from the simulated reduced acquisition with Methods 1, 2 and 3 and averaged over the three readers were 6.7, 0.7 and 1.4%, respectively, with no significant difference between Methods 2 and 3. Interreader and intrareader agreements were excellent with all methods, but interclass correlation coefficients were higher with Method 3. Conclusion: The method using the renal contours should not be used owing to its high proportion of kidneys with a portion excluded from the acquisition. Using the intersection of the left diaphragmatic dome and the anterior margin of the vertebral bodies for proximal landmark for urinary tract CT represents a new alternative method with a better reduction of scan length compared with the method using the inferior margin of T10 and with no significant increase in the number of kidneys with a portion excluded from the reduced acquisition. Advances in knowledge: A new method using the point of intersection of the left diaphragmatic dome and the anterior border of the vertebral bodies on the lateral scout radiograph is introduced to reduce the z-axis coverage of urinary tract CT scans.

The proportion of computed tomography kidneys, ureters and bladder (CTKUB) scans that comply with scan extent protocol in an emergency department: a clinical audit and dose ramification study

“…CTKUBs are common and due to the high reported risks of urolithiasis recurrence (50% in 5–10 years, 75% in 20 years); 2,6 regular, repeated re‐imaging is often necessary, contributing to the patient’s cumulative radiation dose 2,5,7 . Due to the radiation‐sensitive organs (lungs, breasts and gonads) present at the most superior and inferior aspects of a CTKUB scan, scan extent reduction is extremely important 8,9 …”

“…CT topograms in conjunction with scan extent, helical pitch, tube potential, automatic exposure control, manual versus automatic scan cessation and more planning options, allow a patient‐specific tailored CT scan, incorporating patient body habitus, education with breath holds, protocol justification and exhausting non‐radiation medical imaging options if the scan is contra‐indicated 11,12 . CT scan extent limitation is one of the most effective CT dose‐reduction strategies, enabling radiographers to keep the dose ‘as low as reasonably achievable’ (ALARA), 4,8,9,13 in a similar fashion to plain radiography x‐ray collimation.…”

“…Scan extent is operator dependent and directly proportional to the overall dose received 9,11 . Scan extent is planned from a frontal (and at times a lateral) topogram image, in order to plan superior and inferior scan borders of the anatomical region requested 8,9,14 .…”

“…Scan extent is operator dependent and directly proportional to the overall dose received 9,11 . Scan extent is planned from a frontal (and at times a lateral) topogram image, in order to plan superior and inferior scan borders of the anatomical region requested 8,9,14 . However, due to the difficulties in consistently identifying renal contours on topogram images and often unpredictable breathing rates of ED patients, scanning with manual cessation is this department’s CTKUB protocol; starting at the inferior border of the pubic symphysis to the most superior aspect of the kidneys, with a 2 cm over‐scanning tolerance allowed at both borders, for operator accuracy (Table 1).…”

“…The recent literature recommends the use of consistent anatomical landmarks that confidently include the kidneys; mid or inferior margin of 10th thoracic vertebra, 4,9,14 mid or superior margin of the 11th thoracic vertebra, 4,9,14,15 or the intersection of the left or right diaphragmatic dome and the anterior margin of the vertebral bodies, on the topogram images 4,9 . However, this is not possible in patients presenting with vertebral anomalies, where a customised scan is required 4 …”