Ureteral stones are one of the common diseases of the urological system. It is still difficult to diagnose some ureteral stones clinically by using common means such as urological ultrasound, abdominal plain film and intravenous pyelogram. The development of spiral CT technology has provided a faster, safer and more accurate method for the diagnosis of ureteral stones. This paper reviews the application of spiral CT in the diagnosis of ureteral stones. The traditional examination methods are abdominal plain film and intravenous ureterography, and in recent decades, ultrasound, conventional CT and MRI are also used. Since its introduction, spiral CT has obvious advantages: fast scanning speed, the ability to scan the examined area in one breath, rapid thin-layer reconstruction, and the ability to start with axial images and then use three-dimensional images for three-dimensional control and follow-up of lesions in different areas as needed. The interactive viewing of a series of three-dimensional data and the multi-planar reconstruction of images in any direction can greatly improve the diagnosis of small and difficult lesions. The reconstructed images are not interfered by breathing gas, intestinal distension and obesity, etc. It is a new supplement to the urological imaging methods, and it can provide a new, reliable and valuable diagnostic basis for ureteral stones, which is becoming increasingly important and popular. Spiral CT scan is a volumetric scan obtained by continuous 360° rotation of the X-ray tube and detector, and constant forward movement of the examination bed to make the X-ray focus in a spiral motion relative to the patient. This examination has the following features: (1) The patient can complete multiple planes of continuous scanning with one breath hold, no level missed, and multi-level and three-dimensional reconstruction imaging at the suspected lesion site, which improves the diagnosis rate of the lesion. (2) Accurate display of stone location and size to guide clinical formulation of treatment plans. (3) Detection of ureteral stones requires only plain scan without the use of contrast-enhanced scan. This test can still be used for patients with iodine allergy and severely impaired renal function. The obtained volume scan can be processed by 3D stereoscopic imaging to obtain images like venography. (4) Spiral CT can detect negative stones with X-ray transmission and CT values >200 HU, such as cystine, uric acid and xanthine stones, and appropriate treatment can be applied according to the stone density. For example, extracorporeal shock wave lithotripsy can be used for low density stones in the lower ureter and ureteroscopic laser lithotripsy for high density stones in the lower ureter. About 28% of patients with acute low back pain are due to diseases outside the urinary tract. Spiral CT can detect other systemic diseases causing acute abdomen, such as appendicitis, cholecystitis, pancreatitis, ruptured abdominal aortic aneurysm, etc. (6) The examination speed is fast, and all examinations can be completed within 5 min, shortening the examination time for emergency patients and reducing radiation exposure. The increasing popularity of multi-layer spiral CT has made the advantages of spiral CT more obvious. (1) Compared with single-layer spiral CT, the scanning speed of multi-layer spiral CT is increased exponentially. The accelerated scanning speed also improves temporal resolution, voluntary and involuntary motion artifacts (e.g., bowel movements, breathing, heartbeat) are significantly reduced, and patients hold their breath for less time. (2) Improved spatial resolution in the Z-axis, thin layer scanning reduces some of the volume effects and increases diagnostic accuracy. Reduced image noise. For multilayer imaging systems, a longer range of data acquisition can be accomplished by rotating the bulb tube for 1 week, and the current of the bulb tube can be increased without increasing the radiation dose, thus reducing the noise and allowing for better image quality. This is necessary for thin-layer large-range scanning. (3) Multi-layer spiral CT with the same layer thickness and the same time, the scanning range can be expanded exponentially compared with single-layer spiral CT. (4) Increased intravascular contrast concentration during scanning. It can show arterial and venous lesions more clearly, and also has better imaging effect on ureter. (5) Intelligent filtering technology, automatic milliamp modulation and lateral positioning have been adopted to reduce the patient’s exposure dose. The application of spiral CT scan in the diagnosis of ureteral stones has higher sensitivity and specificity compared with conventional examinations. The sensitivity and specificity of spiral CT in the diagnosis of ureteral stones exceeded 95% and 96%, respectively, while the sensitivity of KUB in the diagnosis of ureteral stones was only 45% and the specificity was only 77%, and the sensitivity of ultrasound was 79% and IVU was 52%, which showed that spiral CT was superior to other methods [1]. Sun Zhongyi [10] et al. retrospectively analyzed 81 patients with ureteral stones. 81 cases were scanned with Siemens SOMATOMPlus4 CT machine for full ureteral or selective scan. 96 ureteral stones were detected in 81 patients, 71 cases were unilateral; 35 of them had intravenous and retrograde ureterogram, only 9 cases showed dilated ureter and hydronephrosis on one side. Ultrasound was performed in all 81 cases, 6 cases were suspicious for stones and 75 cases were negative. 81 cases had abdominal radiographs, 3 cases were suspicious for stones and 78 cases were negative. They concluded that 90% of ureteral stones could be detected by KUB plus IVP, and B-ultrasound is also a more common clinical examination method, but the above examination methods are influenced by many factors, which may lead to missed diagnosis or misdiagnosis. The use of spiral CT examination, almost unaffected by breathing, coupled with the rich fatty tissue contrast lining, shows a good, if you can enhance the scan, can exclude the abnormal image interference in the retroperitoneal part of the abdominal cavity, overcome many shortcomings of conventional methods, has the advantages of convenience, fast, does not require special preparation, does not increase the patient’s pain and so on. Acute ureteral calculi are common in the urinary system, and spiral CT is the most effective method for the diagnosis of ureteral calculi with acute renal colic and hematuria as clinical symptoms [2]. Clinical diagnosis is often confirmed by X-ray plain film. Since small stones are easily masked by intestinal gas or stool, etc., and negative stones are not visualized on conventional plain films, their detection rate is low, while spiral CT with continuous volume scanning without interruption, high resolution, and not affected by overlapping of anterior and posterior tissues, its detection rate is significantly higher than that of X-ray plain films. Song Chunxian [6] performed spiral CT plain scan on 28 patients with acute renal colic, and the sensitivity of stones was 100%. 2 of the stones were located in the upper ureter, 4 in the middle segment, and 22 in the lower segment, of which 18 were located at the entrance of the ureteral bladder. 26 of the 28 patients were single, 2 combined with renal stones, and all of them combined with different degrees of pelvic effusion and proximal ureteral dilatation. He believes that spiral CT scan is fast, clear and does not miss small lesions, and is a safe, rapid, non-invasive and effective method for the diagnosis of acute ureteral stones. Spiral “ct can also detect other diseases that cause lumbar abdominal colic such as appendicitis, cholecystitis, pancreatitis, ruptured abdominal aortic aneurysm [14], providing a basis for differential diagnosis. Spiral CT three-dimensional image reconstruction in the diagnosis of ureteral stones Spiral CT is considered one of the best methods for the diagnosis of ureteral stones because of its volumetric scanning, fast scanning speed, strong anti-interference and rapid three-dimensional image reconstruction, which can be observed from multiple angles to determine the relationship between stones and ureter. The workstation of multilayer spiral CT has a powerful post-processing function. After data acquisition and delivery to the workstation, various reconstruction work can be performed, and the main reconstruction methods are: (1) multiplanar refornation (MPR). The main reconstruction methods are: (1) multiplanar refornation (MPR), which is a simple and time-saving operation and is a commonly used reconstruction method; (2) shaded surface display (SSD). (2) shaded surface display (SSD), which can completely show the three-dimensional morphology and spatial location of anatomical structures, with a strong sense of three-dimensionality and realism, and is especially suitable for showing the relationship of complex regional anatomical structures; (3) maximum intensity projection (MIP). (3) maximum intensity projection (MIP), which can be used to make arbitrary rotation along a certain axis and reconstruct the three-dimensional anatomical structure of the sensing tissue and organs from multiple angles; (4) curved planar refornation (CPR). It is an improvement, extension and development of MPR technique, which can reconstruct and present the same organ in the same plane with tortuous paths or even in different planes. The MPR method is generally used for ureteral stones [15], and any of the other three methods or one of them can be used for reconstruction according to the diagnostic needs. Spiral CT combined with 3D reconstruction images can comprehensively, stereoscopically and visually show the extent of ureteral stones and obstructive dilatation, which has important clinical value in diagnosis and differential diagnosis [11]. Wang Xue-chun [7] et al. used SomatomPlus4 spiral CT scanner with layer thickness of 5-8 mm and pitch of 1.5, and scanned 2-3 mm thin layers at the lesion site in 42 patients with ureteral stones, and multiplanar reconstruction (MPR), including sagittal, coronal and oblique reconstruction at any angle, was performed in all cases for observation, and clear localization, characterization and quantification were performed in 40 patients ( Ultrasound confirmed the diagnosis of ureteral calculi in 6/42 cases (14.3%); ultrasound reported dilated renal pelvis and ureter, but failed to report the cause of obstruction and the presence of ureteral calculi in 33/42 cases (78.6%); 3 cases (7.1%) did not show any abnormality. Geng Cai-Zheng [8] performed whole ureter non-enhanced spiral CT scan with coronal and sagittal surface reconstruction in 11 patients. The reconstructed images all clearly showed the entire ureter. Ten of them showed that the stones were located in the ureteral lumen, and also showed the size, morphology, location and the degree and extent of ureteral obstruction dilatation. Rexiong You [9] performed total ureteral scan or/and renal artery phase, renal parenchymal phase, and excretory phase total ureteral scan in 34 patients with the main clinical symptoms of lumbar pain, lumbar acidity, and hematuria, and the duration of disease ranged from 3 d to 13 yrs. After scanning, 3D post-processing techniques including multi-planar reconstruction (including oblique and curved surface reconstruction), volume reconstruction, and maximum density projection were used for 3D image reconstruction. The results showed that all stones were clearly displayed, and the flat scan showed a dense shadow in the ureteral lumen, and the stones in MPR images were shuttle-shaped or irregular, in the same direction as the ureteral alignment, with different degrees of ureteral dilatation above, and the marginal sign was visible. Ultrasound is a screening method for the diagnosis of ureteral stones, but the lack of a “window of sound” in the ureter as a background for the stones and the influence of gas in the intestine make detection poor, and sometimes the operator’s experience limits the ability to misinterpret the intestinal light mass as a stone. The most basic method to diagnose ureteral stones, usually the detection rate of X-ray plain film is only 60%, and negative stones (oxalic acid stones) cannot be detected. Due to the small size of ureteral stones in general and the obscuring factors from the transverse spine and pelvis, in fact, 50% of ureteral stones in patients with acute renal colic attacks are difficult to be identified [1]. routine examination, but like KUB, it is affected by stone composition, size, bowel and bone. IVU requires contrast injection, which has the potential to cause acute allergic reactions, and the time required for the examination is at least 45 min, which may extend to 1 to 2 h if the contrast is poorly developed, prolonging the patient’s pain and increasing the exposure time to X-rays. At the same time, patients with renal colic experience a transient decrease in the function of the affected kidney, which is generally not or very poorly visualized with conventional doses of IVU. In addition, IVU is contraindicated in patients with renal insufficiency with serum creatinine >266 mol/L. Plain CT requires a delay of 5 to 10 seconds between each two-layer scan, while spiral CT is volumetric because it is a volume scan. Fast scanning speed, strong anti-interference and rapid three-dimensional reconstruction can be performed to find the relationship between stones and ureter from multiple angles of observation. It is especially suitable for ureteral stones that cannot be diagnosed by other imaging examinations during acute renal colic attacks, and is not affected by the large composition, size and location of the stone or the patient’s obesity, and can reflect the condition of the ureter, pelvic effusion and surrounding organs above the stone. Spiral CT also has shortcomings, as the radiation dose of normal spiral CT is significantly higher than that of IVU [3], but low-radiation spiral CT has improved this situation. On balance, he concluded that low-radiation spiral CT is significantly better than IVU. Ureteral stones on spiral CT scan show a direct sign of high density and a “rim sign”, which is formed by edema of the tissue surrounding the stone. Indirect signs include hydronephrosis, ureteral effusion, perinephric striae, meganephrosis, periureteral edema, and asymmetry in the density of both kidneys [15]. One study [12] stated that the probability of ureteral hydronephrosis in patients with ureteral stones was 82.7%; hydronephrosis 80%, periureteral edema 59%, and dilated renal pelvis 57.2%. Therefore, the combination of indirect signs of ureteral stones is beneficial to improve the accuracy of spiral CT in the diagnosis of ureteral stones. Pelvic vein stones can be distinguished from ureteral stones on spiral CT scan by the comet-tail sign, and the border sign has also been reported. It can also be used as a differentiating sign [13]. In conclusion, spiral CT is the best means to detect and localize ureteral stones because it is non-invasive, painless, requires no bowel preparation, and is accurate and reliable for diagnosis and localization.