EVALUATION OF CERVICAL SPONDYLOSIS USING 0.2 TESLA AXIAL T2 AND AXIAL 3D FIESTA MAGNETIC RESONANCE IMAGING SEQUENCES

CHAPTER ONE

INTRODUCTION: Background of the Study

In contemporary clinical practice, neck pain according to Rana et al., (2011), is prevalent in approximately 15% of the general population. Cervical spondylosis is a disorder of the cervical spine and it is a common cause of neck pain (Takagi et al, 2001). It is characterized by chronic intervertebral disc degeneration, abnormal wear on the cartilage and bones of the cervical spine. According to Okada et al., (2009), cervical spondylosis is categorized into three clinical syndromes:

1. Cervical radiculopathy due to compression, stretching or angulations of the cervical nerve root.

2. Cervical myelopathy due to compression, compromised blood supply or recurring minor trauma to the cord.

3. Axial joint pains.

They also state that both sexes are affected equally from the age of 50 years but the problems begin earlier in males.

Sutton (2004) opines that cervical spondylosis is indicated as radial (anterior) tearing of the annulus fibrosus, loss of disc height, dehydration and fissuring of the disc and osteophytes development anteriorly in association with anterior annular tear and nerve root compression. However, the tearing of the annulus fibrosus of the intervertebral disc occurs from about30 years to 40 yearsof age (Sutton 2004). At times, the diseased condition may be asymptomatic, since there are such conditions as pain, myelopathy and radiculopathywhich may be asymptomatic but later degenerate to a complicated state, there is need therefore for early detection of this disease condition. Early diagnosis aids better patient management. This may overcome the challenge of asymptomatic cases of cervical spondylosis.

Axial T2 sequence is a Fast spin echo sequence. Fast imaging employing state acquisition (FIESTA) is a steady state gradient echo sequence in which residual transverse magnetization is refocused so that a steady magnitude of longitudinal and transverse magnetization is achieved after a few repetition (TR) periods. Once a steady state is reached it produces free induction decay signal and spin echo signal. It is called FIESTA–Fast imaging employing steady state acquisition or SSFP (Balanced steady state free precision sequence) or FISP-(Fast Imaging with Steady State Precision) (Bhosale et al., 2008). The image contrast in FIESTA is determined by the T2: T1 ratio of the tissue. Tissues with long T2 relaxation time and short T1 relaxation time (for example water and fat) have high signal intensity. This is the reason for excellent contrast between cerebrospinal fluid and other structures. Advantages of FIESTA include: Short imaging time, high signal–to–noise ratio (SNR), better contrast–to-noise ratio (CNR) and high spatial resolution. (Scheffler et al,2003;Meindi et al, 2009).

The cervical spine is located between the head and the thoracic spine. It consists of seven vertebrae. The vertebrae are surrounded by anterior longitudinal ligament, posterior longitudinal ligament and muscles. The articulating surfaces of adjacent vertebrae are connected by intervertebral discs as well as the ligaments. The disc comprises of annulus fibrosus surrounding a gelatinous nucleus pulposus. The first two vertebrae are called the axis and atlas and do not have a disc between them but are closely related by a ligament. The spinal canal is widest between the first cervical vertebra and the third cervical vertebra (AP diameter is about 16-30mm) and it narrows as it progresses gradually (14-23mm). The cervical spine has foramina on each side which all vertebral arteries passes through (Binder et al., 2007).

The cervical spines contain and protect the spinal cord, support the weight of the skull and enable diverse movement with the aid of the ligaments and muscles around it. Imaging modalities used for evaluation of cervical spondylosis include plain radiography, computed tomography, computed tomographic myelography, magnetic resonance imaging, discography and radionuclide imaging.

Plain radiography demonstrates ageing changes such as loss of disc height and bone spurs. However, it is a two dimensional imaging technique which cannot display the acquired images in coronal, axial and sagittal plane.

Computed tomographic myelography evaluates the spinal canal, cerebrospinal fluid and nerve root, but it has the risk of contrast morbidity and at times the procedure may not be successful (Orthol, 2009). Computed tomography can be used to assess the bone and the spinal canal.

Magnetic resonance imaging is a non-invasive medical imaging modality that uses strong magnetic field, radio frequency waves, body coils and computer display unit. Magnetic resonance imaging has been widely accepted as the gold standard in diagnosis of cervical spondylosis. This could be due to better soft tissue characterization that allows direct evaluation of ligaments, spinal cord, disc contents and vasculature around the neck. Also, it uses non-ionizing radiation.These advantages make it the preferred modality for diagnosis of cervical spondylosis. However, MRI has some limitations;it is expensive and it is always not readily available, it also takes longer scan time, and patients with metallic implant cannot undergo the investigation. (Holmes et al, 2002;Mansfield2003; RSNA 2006 and Newman et al, 2013).

Over the years, sagittal T1, T2 and axial T1, T2 have been used as the standard MRI protocols for diagnosis of cervical spondylosis. Sagittal protocol only shows reduction in disc height, disc herniation, dehydration of disc content and spikes.Axial MRI protocol on the other hand, is the gold standard to evaluate disc tear (of annulus fibrosus and nucleus polposus),disc prolapse, disc protrusion, disc herniation and nerve root compression(Morishita et al,2005;Al-Shatoury et al, 2009;Newman, et al, 2013). Axial 3D fast imaging employing steady state acquisition (FIESTA) is an additional protocol which gives images of high signal-to-noise ratio within a short time and produces better contrast due to its insensitivity to motion.

In UsmanuDanfodiyo University Teaching Hospital (UDUTH), the number of patients referred for MRI scan of the cervical spine due to cervical spondylosis has been on the increase. This study is intended to compare the accuracy of axial T2 with axial 3D FIESTA protocols in diagnosis of cervical spondylosis. This may help in deciding which protocol to use in investigating cases of cervical spondylosis.

1.2 Statement of Problem

Although axial T2 MRI protocol has remained the gold standard for better assessment of the structures affected by cervical spondylosis (Newman et al, 2013), T2 is subject to artefacts (flow artefact). An MRI protocol that is insensitive to flow artefacts with high signal to noise ratio and shorter scan time (compare with axial T2) might be more accurate than axial T2 in detecting structures affected by cervical spondylosis. Is axial 3D FIESTA really subjective to less artefacts and increased image quality when compared with axial T2 MRI sequences?

1.3 Purpose of the Study

The purpose of this research is to compare axial T2 MRI protocol with axial 3D FIESTA

MRI protocol in cervical spondylosis.

The specific objectives of the study are:

1. To compare the accuracy of axial T2 MRI and axial 3D FIESTA MRI in the diagnosis of cervical spondylosis.

2. To compare the image quality(signal-to-noise ratio, contrast -to-noise ratio and image artefact) produced from both protocols.

3. To ascertain the association of the magnetic resonance imaging findings of cervical spondylosis with age and sex.

1.4 Significance of the Study

1. The outcome of the study will define MRI protocol that could aid early and more accurate diagnosis of cervical spondylosis even in asymptomatic cases. Early diagnosis of the disease will enable early and better treatment.

2. The outcome of this study will help to establish which magnetic resonance sequence gives better image quality in cases of cervical spondylosis.

3. The association of the occurrence of cervical spondylosis with age and sex will establish which sex and age group are more prone to the disease. This will help in early detection and better patient management.

1.5 Scope of the Study

This prospective study on cervical spondylosis was carried out at MRI unit in the Department of Radiology, UsmanuDanfodiyo University Teaching Hospital, Sokoto.

1.6 Hypothesis

HO: Axial 3D FIESTA is as accurate as Axial T2 in the evaluation of cervical spondylosis

H1: Axial 3D FIESTA is not as accurate as Axial T2 in the evaluation of cervical spondylosis

1.7 Definition of Terms

T1 Recovery

T1 Recovery is the recovery of 63% of original value of longitudinal magnetization following an excitation pulse by radiofrequency wave (Allisy et al., 2008).

T1 Time

T1 Time is the time it takes for excited spin to recover and be available for the next excitation(Allisy et al., 2008;Jagon et al., 2008).

T2 Relaxation

T2 Relaxation is the decay of transverse magnetization to 37% of its initial value immediately after excitation(Allisy et al., 2008).

T2 Time

T2 Time is the time it takes for magnetic resonance signal to fade after excitation(Allisy et al., 2008; Jagon et al., 2008).

Time of Echo (TE)

Time of echo or echo time is the interval between application of the excitation pulse and collection of the magnetic resonance signal. It controls T2(Chavan et al, 2007).

Repetition Time (TR)

Repetition time is the interval between two successive excitation of the same slice. It controls T1(Allisy et al., 2008).

Proton Density (PD)

Proton density is the number of excitable spins per unit volume (Mansfiield, 2003). T1 Weighting (T1W)

T1 Weighting involves eliminating T2 effect/contrast in order to enhance T1 effect/contrast (Bushberg 2001).

T2 weighting (T2W)

T2 weighting involves eliminating T1 effect to enhance T2 effect (Bushberg 2001).

Signal-to-Noise ratio (SNR)

Signal-to-Noise ratio is the ratio of useful signal to the noise generated during magnetic resonance scan(Jagon et al., 2008).

Contrast-to-Noise ratio

Contrast-to-Noise ratio is the difference in SNR between two adjacent areas(Jagon et al., 2008). Number of Excitation (NEX)

Number of excitation is the number of times a signal from a given slice is measured(Allisy et al., 2008).

Saturation Band

Saturation Band is used to suppress undesired signal from the tissue within the imaging volume(Allisy-Roberts et al., 2008).

Gradient Echo (GRE) Sequence

This is a sequence that employs the gradient coil for producing an echo rather than pairs of radiofrequency pulses(Chavan et al., 2007).

Spin Echo (SE)

SE pulse sequence utilizes 900 excitation pulse to flip the net magnetic vector into the transverse plane(Chavanet al., 2007).

Fast or Turbo Spin Echo Sequence

This is a modified spin echo sequence with considerably shorter scan times (Jagon et al.,2008;Allisy et al., 2008)