The comparative study on axial and coronal CT images using maximum intensity projection for evaluating urinary calculus - a study protocol

Introduction

The Renal Calculi or kidney stones are crystal aggregates within the kidney. Nephrolithiasis is a Greek word. Nephrosis means “kidney”, and lithos means “stone”. It refers to kidneys having stones or calculi in the collecting system. Kidney stones (or) Nephrolithiasis exclusively refers to the presence of calculi (or) stones in the kidneys.¹ Renal stones continue to be a prevalent issue, impacting around 10% of individuals at some stage. The occurrence of kidney stones has risen in recent years, although this could be partially attributed to enhanced identification methods.²

For patients who are complaining of acute flank pain and feeling of urolithiasis, unenhanced C.T. is the imaging modality of choice. However, not every patient in this situation has stone illness; others have a different diagnosis for their acute pain, such as diverticulitis, appendicitis, or even pancreatitis.³

Contrary to urolithiasis, contrast-enhanced C.T. (C.E.C.T.) is a better tool for evaluating these entities. It can be challenging to clinically distinguish between these conditions and stone disease, and some patients may need clarification on whether a C.T. scan should be done with or without contrast. Additionally, pyelonephritis and renal abscess, which could mimic or worsen symptomatic urolithiasis, are challenging to detect on unenhanced CT.⁴

Few studies have specifically looked at the phenomena that have been Theorized to decrease the sensitivity of C.T. for identifying renal stones.

Maximal-intensity projection (M.I.P.) techniques generate a two-dimensional image by projecting a line (or search ray) through a dataset in a given volume, highlighting the voxel with the highest attenuation value. M.I.P. is commonly used in C.T. angiography for evaluation and display purposes.⁵

In our study, we explored the effectiveness of coronal M.I.P. reformations in detecting and measuring the Hounsfield density of urinary tract stones. We hypothesized that the improved visibility of stones on M.I.P. images would enhance the detection of urinary tract stones compared to regular axial and coronal reformats. Additionally, since M.I.P.s eliminate partial volume-averaging effects, density measurements may be more precise.⁶

The purpose of the study is to identify which CT Projection (Axial, Coronal M.I.P.) is best for the Detection of Renal stones; the current study was to compare the detection rate and size measurements of Renal calculi on Axial And coronal MIP images.

Protocol

Methodology

Over two years, we plan to recruit 120 patients over the age of 18 who have been referred to A.B.V.R.H. hospital. The study will focus on the visible anatomy and specific information regarding the size, shape, and location of the urinary stones and the techniques used to capture the images.

During the study, we will compare the calculus size measurements in three planes: A.P. × TRANS × CRANIOCAUDAL between the C.T. Axial, Coronal, and CT M.I.P. Axial and Coronal images, with a focus on stones measuring 4 mm, 6 mm, and 8 mm with your innovative study, you hope to provide valuable insights into the efficacy of using maximum intensity projection for the evaluation of urinary calculus, potentially paving the way for improved diagnostic and treatment options for patients.

Discussion

The results of the study suggest that thin images obtained from contrast-enhanced C.T. (CECT) during the portal venous phase are highly effective in detecting renal stones measuring 2 mm or larger. However, for patients experiencing acute flank pain with suspected renal stone disease, unenhanced C.T. is still the recommended imaging test. Traditionally, C.E.C.T. has been considered inadequate for detecting renal stones and is not recommended in such cases. Flank pain can be caused by conditions other than urolithiasis, and various renal disorders can present similar symptoms.⁷ This poses a challenge in selecting the most suitable imaging protocol when evaluating patients suspected of having urolithiasis along with other conditions like appendicitis or diverticulitis.

If contrast material is used to optimize the evaluation, it is important to be aware of the sensitivity of C.E.C.T. in detecting renal stones.⁸ The reduced sensitivity of C.E.C.T. in this regard is attributed to the enhanced appearance of the kidneys, which diminishes the contrast between the stones and the renal parenchyma. Recent studies have reported varying sensitivities in detecting renal stones with C.E.C.T.⁹ One study found an overall sensitivity of 81% for detecting renal stones, with higher sensitivity for larger stones. Another study focusing on arterial phase CT detected 75% of renal calculi and all stones larger than 5 mm. The differences in sensitivities could be due to variations in slice thickness, as thinner slices have been shown to enhance renal stone detection on unenhanced CT.¹⁰

Thin images from portal venous phase C.E.C.T. demonstrate high sensitivity in detecting renal stones measuring 2 mm or larger. However, for patients with acute flank pain and suspected renal stone disease, unenhanced CT remains the recommended imaging test. C.E.C.T. has historically been deemed inadequate for detecting renal stones and is not recommended for this purpose.¹¹ It is important to consider the challenges in accurately diagnosing renal stones, as other conditions can mimic urolithiasis symptoms. The choice of imaging protocol should be carefully considered, taking into account potential alternative conditions and the sensitivity of C.E.C.T. in detecting renal stones. Thinner image slices have shown improved detection of renal stones on unenhanced CT.¹²